Recent Advances in Corpus Luteum Physiology1, Slides of Endocrinology

Download Recent Advances in Corpus Luteum Physiology1 and more Slides Endocrinology in PDF only on Docsity! SYMPOSIUM: OVARIAN FUNCTION Recent Advances in Corpus Luteum Physiology 1 M I C H A E L F. SMITH Department of Animal Science University of Missouri Columbia 65211 ABSTRACT Development, maintenance, and re- gression of the corpus luteum have been investigated for many years. However, endocrine and cellular mechanisms reg- ulating progesterone synthesis and secre- tion remain unclear. Because compre- hensive reviews of factors affecting luteal function have been published recently, this paper discusses several emerging concepts that may be important in understanding the regulation of luteal progesterone synthesis and secretion. Concepts discussed include preovulatory follicular determinants of subsequent luteal function, hormonal stimulation of progesterone synthesis, effect of different luteal cell types on progesterone secretion, and role of secretory granules in luteal function. I N T R O D U C T I O N The corpus luteum is a transient endocrine gland that develops from a Graafian follicle following ovulation. The corpus luteum secretes progesterone and has an important regulatory role; length of estrous and menstrual cycles are determined by duration of progesterone secre- tion. Artificial control of plasma progesterone concentrations has important practical ap- plications for controlling time of ovulation and has been the focus of numerous studies (18, 70, 83). Luteotropic and luteolytic mechanisms regulating luteat lifespan and function are not completely understood; however, secretions from the anterior pituitary gland, uterus, ovary, embryo, and placenta are involved in the control of progesterone secretion (16, 68, 69, Received July 8, 1985. 1 Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 9906. 86, 133, 135, 136, 153). Because several excellent review articles on the regulation of corpus luteum function have been published, this paper discusses recent findings that are or may prove to be important in understanding regulation of luteal lifespan and mechanisms associated with progesterone synthesis and secretion. Particular attention is given to: 1) preovulatory follicular determinants of luteal function, 2) hormonal stimulation of pro- gesterone synthesis, 3) effect of different luteal cell types on progesterone secretion, and 4) role of secretory granules in luteal function. Em- phasis will be given to cattle and other livestock species whenever possible. P R E O V U L A T O R Y F O L L I C U L A R D E T E R M I N A N T S OF LUTEAL FUNCTION Corpora lutea are a continuation of follicular maturation and develop from both granulosa and theca cells in pigs (26), sheep (192), and cattle (4, 36); therefore, extrafollicular and intrafollicular events affect subsequent luteal lifespan or function. Extrafollicular Events Preovulatory follicular maturation in rats (146), pigs (41), sheep (127), cattle (70), and several other species results from the coordinated actions of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) on theca and granulosa cells, respectively. Following LH stimulation, theca interna synthesizes androgens, which subsequently diffuse through the base- ment membrane. Within granulosa cells, andro- gens are converted to estradiol-17/3 by aromatase, an enzyme regulated by FSH (69, 146). Within a growing follicle FSH also is associated with granulosa cell proliferation, antrum formation, maintenance of granulosa cell viability (in vitro), and synthesis of gonadotropin receptors on granulosa cells (112, 140, 146). For a comprehensive review of the actions of LH and FSH on granulosa cells see Hsueh et al. (82). 1986 J Dairy Sci 69:911-926 911 912 SMITH Because ovulation does not guarantee normal luteal development and function, endocrine and cellular changes during follicular development can affect the subsequent corpus luteum. Currently, it is unclear whether fol- licular events at the time of follicular re- cruitment or events during the preovulatory period are most directly associated with sub- sequent luteal function. In women and primates, decreased plasma FSH concentrations or an inadequate FSH to LH ratio during the preovulatory period was followed by subnormal luteal function (35, 170, 180, 197). Furthermore, temporary suppression of preovulatory plasma FSH, but not LH concentrations, induced by in- jections of follicular fluid (presumably inhibin), reduced luteal weight and plasma progesterone secretion during the subsequent cycle (178). Suppression of postovulatory plasma FSH and LH concentrations in primates did not affect luteal lifespan or plasma progesterone secretion (13). Alternatively, increased gonadotropin con- centrations during the follicular phase enhanced progesterone secretion during the subsequent cycle in primates. Luteectomy during the midluteal phase of the primate cycle was followed by a transient increase in plasma FSH and LH concentrations, which was greater in unilaterally ovariectomized than in intact monkeys (64). Furthermore, plasma pro- gesterone secretion by the corpus luteum formed following luteectomy tended to be greater in unilaterally ovariectomized than intact monkeys (62, 63). In a subsequent experiment (174), magnitude of the transitory gonadotropin release following luteectomy was positively correlated with basal and human chorionic gonadotropin (hCG)-stimulated pro- gesterone secretion (in vitro) by the subse- quently formed corpus luteum. Although the follicular phase in cattle and sheep is considerably shorter than in humans and primates, preovulatory FSH concen- trations also might be important for the forma- tion of a normal corpus luteum in the former species. In both cows and ewes a decrease in preovulatory FSH, but not LH, concen- trations was detected prior to a short versus a normal length cycle (115, 143). These results are particularly interesting since pulsatile injections of GnRH (2 /~g every 2 h) for 72 h prior to a gonadotropin-releasing hormone (GnRH) challenge (50 /.tg) in postpartum anestrous dairy cows resulted in normal length estrous cycles, whereas a GnRH challenge preceded by saline injectons resulted in short cycles (124). In addition to FSH, progesterone contributes to the preovulatory endocrine environment and can affect subsequent luteal function. Early weaning of anestrous cows or injection of anestrous cows and ewes with GnRH resulted in formation of short lived corpora lutea unless the animals were pretreated with a progestogen (72, 110, 141,142, 187). Furthermore, follicles that were not exposed to progesterone for an extended period of time, due to repetitive removal of the preovulatory follicle at estrus, formed subnormal corpora lutea in ewes (24). It is unclear whether the effect of pro- gesterone priming on subsequent luteal function was due to the modulation of preovulatory gonadotropin secretion or to a direct effect on the preovulatory follicle. In anestrous ewes repeatedly injected with low doses of GnRH, the LH surge was delayed in animals pretreated with progesterone (111). These results agree with a previous study (89) in which progesterone delayed the estradiol-induced LH surge in ewes. A delayed LH surge might extend preovulatory follicular development due to a longer exposure to gonadotropin stimulation. However, McLeod and Haresign (110) reported that a delayed LH surge was not totally responsible for normal luteal function in progesterone primed ewes and suggested that progesterone also may increase the responsiveness of the preovulatory follicle to gonadotropin stimulation. In cycling cows, elevated plasma progesterone concentrations during the luteal phase were followed by reduced plasma progesterone concentrations during the subsequent estrous cycle (122, 150). Although the mechanism is unclear, elevated progesterone concentrations may alter patterns of follicular development, resulting in subnormal luteat function during the subsequent cycle. In monkeys, follicular maturation was inhibited by progesterone even though plasma FSH concentrations were elevated (63). Intrafollicular Events McNatty (112) suggested that development of a normal corpus luteum may depend upon a Journal of Dairy Science Vol. 69, No. 3, 1986 SYMPOSIUM : OVARIAN FUNCTION 915 steroidogenic enzymes (i.e., cholesterol esterase and side-chain cleavage complex), thus increasing progesterone synthesis. Furthermore, protein kinase may increase the synthesis of specific proteins that transport substrates to steroido- genic enzymes or remove progesterone, thus reducing end-product inhibition of enzymatic activity (20). Luteal LH receptors are located on the plasma membrane and in rats hCG binding was concentrated on the cell surface having micro- villi and adjacent to capillaries (11). Hormone- receptor binding is dependent upon the hormone concentration, affinity of hormone binding, and receptor concentration. Because plasma LH concentrations remain low during the luteal phase and do not parallel progesterone con- centrations, an increase in LH-receptor affinity or receptor number would be expected. In primates (21), sheep (34), and cattle (144) an increase in LH receptor affinity was not observed during the luteal phase. Number of luteal LH receptors and secretion of progesterone during the cycle were positively correlated in primates (21), women (97), rats (66, 98), sheep (34), horses (151), and cattle (40, 55, 144, 175). In cattle, the concentration of occupied luteal LH receptors was not correlated with progesterone secretion. However, number of occupied LH receptors per corpus luteum was correlated with progesterone secretion as previously reported in ewes (34). During the bovine estrous cycle, unoccupied luteal LH receptors increased during luteal development (47, 55, 144, 175) and decreased after luteal regression (47, 55,175). Cyclic AMP might be an important mediator of progesterone synthesis (106, 107) and the intracellular concentration of this cyclic nucleo- tide is regulated by changes in adenylate cyclase and phosphodiesterase activities. Ling et al. (101) reported that guanosine-3 ~, 5'-mono- phosphate (cyclic GMP) was not involved in LH stimulation of progesterone synthesis by bovine corpora lutea. Mechanisms associated with receptor- adenylate cyclase interactions have been reviewed in detail (38, 154, 176, 200) and are briefly summarized. Activation of adenylate cyclase involves a regulatory and a catalytic subunit. Following hormone binding, the hormone-receptor complex interacts with the regulatory subunit and increases guanosine triphosphate (GTP) binding. The GTP-bound regulatory subunit activates the catalytic subunit, which converts ATP to cAMP. Fol- lowing hydrolysis of GTP to guanosine diphos- phate (GDP), the regulatory subunit dissociates from the catalytic subunit and the enzyme is inactivated (176). In cattle, luteal adenylate cyclase activity increased during luteal development and decreased during luteolysis (47, 55). Bovine luteal adenylate cyclase activity was correlated positively with progesterone secretion, sug- gesting a n interaction among LH receptor concentrations, adenylate cyclase activity, and progesterone secretion in cattle (55). During luteolysis a decrease in luteal LH receptors is not responsible for decreased progesterone secretion in primates (21), ewes (34), mares (152), and cows (47, 175). However, a decrease in adenylate cyclase activity may be associated with luteolysis. A decrease in luteal adenylate cyclase activity, which was associated with a decrease in plasma progesterone concentration, has been reported in sheep (3) and cattle (47) during prostaglandin F2& (PGF2a)-induced luteolysis. Furthermore, luteal regression in swine was accompanied by a decrease in luteal adenylate cyclase activity (6) and a decrease in luteal cAMP concentration (95). A decrease in adenylate cyclase activity might result in lowered intracellular cAMP concentrations, thus decreasing progesterone synthesis (107, 135). However, other factors, such as decreased luteal blood flow to the corpus luteum, cannot be ignored as a possible luteolytic mechanism (131, 134). Phosphodiesterase is located in the cytosol and membrane fractions of most tissues and assists in regulating intracellular cAMP con- centration by hydrolyzing the cyclic nucleotide to 5'-AMP [(Figure 1;(186)]. Phosphodiesterase activity consists of multiple forms of the enzyme, which can be regulated by certain nucteotides, divalent ions, and hormones (186, 195). Decreased phosphodiesterase activity was not involved in LH stimulation of progesterone secretion. However, a increase in phospho- diesterase activity might be involved in de- creasing progesterone secretion. As corpora lutea aged, there was a concomitant increase in phosphodiesterase activity in rats (177) and cattle (55). Furthermore, in ovine luteal tissue, phosphodiesterase activity increased within 4 h Journal of Dairy Science Vol. 69, No. 3, 1986 916 SMITH after PGFza injection (3). A simultaneous increase in phosphodiesterase activity and a decrease in adenylate cyclase activity may decrease intracellular cAMP concentrations and thus decrease progesterone synthesis. As previously mentioned, an increase in intracellular cAMP concentration reportedly can activate protein kinase activity and ulti- mately stimulate steroidogenesis. In bovine corpora lutea, LH stimulated cAMP-dependent protein kinase activity (30), and a positive correlation between stimulation of protein kinase activity and progesterone synthesis has been reported (100). Mechanisms by which cAMP-dependent protein kinase activity might stimulate progesterone synthesis have been reviewed elsewhere (107, 135). Although previous studies have indicated that cAMP is important for progesterone synthesis, changes in adenylate cyclase activity and progesterone synthesis are not always correlated. In addition, luteal adenylate cyclase activity is less responsive to LH stimulation in sheep and cattle (3, 104, 105) than in rats and rabbits (84, 85). In sheep and cattle, endogenous hormone bound to luteal tissue may increase basal activity such that stimulation with exogenous hormone is reduced. However, in bovine luteal tissue there was no correlation between the occupied LH receptor concen- tration and basal adenylate cyclase activity (55). Furthermore, Hoyer et al. (81) demon- strated that an increase in intracellular cAMP concentrations in large (>20 /~m) ovine luteal cells was not accompanied by an increase in progesterone secretion. Consequently, pro- gesterone secretion by large ovine luteal cells already may be maximally stimulated, or cAMP may just have a permissive role in progesterone secretion, or progesterone secretion may occur by a cAMP-independent mechanism. Pbospbolipid Metabolism. A new concept of hormone action is emerging, which involves phospholipid metabolism within the plasma membrane and may be associated with luteal progesterone synthesis. The plasma membrane consists of a phospholipid bilayer interspersed with proteins (171). Upon binding to specific membrane receptors, protein hormones can initiate changes in membrane phospholipids, which may be important for signal transduction (43, 108, 132). Recent evidence implies that phospholipid methylation or phosphatidyl- inositol metabolism may be associated with LH-stimulated progesterone secretion by bovine luteal cells. Hirata and Axelrod (77) proposed that phospholipid methylation is a mechanism for signal transmission through the plasma mem- brane. Stimulation of progesterone secretion by LH was increased or inhibited when a stimulator or inhibitor of phospholipid methylation was added to dispersed bovine luteal cells, re- spectively (117). Stimulation of progesterone secretion by either direct activation of adenylate cyclase or addition of cAMP to dispersed bovine luteal cells was not altered by stimulators or inhibitors of phospholipid methylation. Consequently, the mechanism by which phos- pholipid methylation increased progesterone secretion either preceded or was independent of cAMP synthesis. Phospholipid methylation increases membrane fluidity (77) and following LH binding may unmask additional LH recep- tors and perhaps enhance activation of adenylate cyclase by the LH-receptor complex as pre- viously suggested (77, 78, 117). Hormonal stimulation of steroidogenesis may be mediated by changes in phosphatidyl- inositol metabolism [Figure 2; (43)]. Hor- mone binding is followed by enzymatic break- down of a polyphosphoinositide (phosphatidyl- inositol-4, 5-bisphosphate) into inositol- triphosphate and diacylglycerol, which act as second messengers to elicit a cellular response (43, 132). Inositol triphosphate releases intra- celluiar calcium (179) whereas diacylglycerol activates a calcium-dependent protein kinase [protein kinase C; (23, 132)]. Following a series of conversions, inositol triphosphate and diacylglycerol are combined to resynthesize phosphatidylinositol-4,5-bisphosphate (108). In bovine luteal tissue, LH stimulated changes in phospholipid metabolism (primarily phosphatidylinositol), which were related both by dose and time to changes in progesterone secretion (33). In this study, cAMP stimulated progesterone secretion but did not alter phos- pholipid metabolism;consequently, LH-induced phospholipid changes are probably independent of an increase in cAMP. Recently a phospho- lipid-sensitive, calcium-dependent protein kinase was identified in the corpora lutea of cattle (32), rats (31), and humans (90). However, it is not known whether this protein kinase is controlled by LH. The presence of a calcium- Journal of Dairy Science Vol. 69, No. 3, 1986 S Y M P O S I U M : O V A R I A N F U N C T I O N 917 Receptor Protein Kinase C ~-z+ . . . . . . .~,. . o e , . . . . . . o n Cellular ~ ~ ' - ' ~ Caz+ Response Figure 2. Proposed role of polyphosphoinositides in hormone action. Following hormone binding an enzyme cleaves phosphatidylinositol-4, 5-bisphosphate (PIP 2) into diacylglycerol (DG), which activates a calcium-dependent protein kinase (protein kinase C) and inositol triphosphate (IP 3 ), which in turn mobilizes calcium (Ca 2+) from intracellular stores. Activation of protein kinase C results in a cellular response. Resynthesis of PIP 2 includes the following steps: phosphate groups are sequentially removed from IP 3 to form inositol bisphosphate (IP2), inositol phos- phate (IP), and inositol (I). Diacylglycerol forms phosphatidic acid (PA) and is converted to the cyto- sine nucleotide derivative (CDP-DG). Inositol and CDP-DG are combined to form phosphatidylinositol (PI). Phosphorylation of P1 forms phosphatidylnositol- 4-phosphate (PIP) followed by formation of PIP 2. dependent protein kinase in luteal tissue is particularly interesting since calcium is re- portedly required for LH-induced progesterone secretion by ovine luteal cells (76) and porcine granulosa cells (189, 190). EFFECT OF D I F F E R E N T LUTEAL CELL TYPES ON PROGESTERONE SECRETION The corpus luteum contains a heterogeneous population of ceils that differ in size, appearance of organelles, and steroidogenic capability (28, 48, 54, 92). Steroidogenically active luteal cells include both small and large cells in rats (196), monkeys (28), humans (29), pigs (99), sheep (48), cattle (92,188) , and deer (172). The origin of different luteal cell types has been controversial. In ovine and bovine corpora lutea, small cells are reportedly derived from theca cells and large cells derived from granulosa cells (4, 36, 54, 137). However, it also has been suggested that large luteal cells are derived from small luteal cells (4, 36, 48), and this transition may be regulated by LH (44). During the ovine estrous cycle, large luteal cells first appeared about d 8 postestrus and increased in number on d 12, 14, and 16 (48). These results suggest that small luteal cells can develop into large luteal cells as luteal age increases. Similar results have been reported for the bovine estrous cycle. Alila and Hansel (4) utilized monoctonal antibodies directed against surface antigens of bovine theca and granulosa ceils to determine the follicular origin of different sized luteal cells and changes in the small to large cell ratio during the bovine estrous cycle. They reported that small and large iuteal cells originated from theca and granulosa cells, respectively. Fur- thermore, small iuteal cells developed into large luteal ceils as the luteal phase progressed. Interpretat ion of these results assumes that the follicular antigens to which the monoclonal antibodies were developed did not change over time. Currently, it is not clear whether this assumption is valid. Consequently, the follicular origin of small and large luteal cells remains unclear. Because the ultrastructure and steroidogenic capability of small and large luteal cells differ, it is conceivable that both cell types are involved in the regulation of progesterone secretion. An interaction between steroidogenic cell types (theca and granulosa) within the follicle to synthesize estradiol-17/3 has been described already (146). Addit ionally, synthesis of testosterone and adrogen-binding protein by interstitial ceils and Sertoli cells, respectively, is another example of the coordinated activities of two cell types within a reproductive tissue (5). There are distinct differences in the abili ty of small and large luteal cells to secrete pro- gesterone in the presence or absence of LH. In pigs (99), sheep (48), and cattle (92, 188) basal progesterone secretion was lower in small relative to large luteal cells; however, LH- stimulated progesterone secretion was greater in the small cells. Specifically, large bovine luteal cells secreted 20 times as much progesterone as small luteal cells. However, small luteal cells were 6 times more responsive to LH than large luteal cells (92). In sheep, small luteal cells have more LH receptors and fewer PGF2a and prostaglandin E2 (PGE2) receptors than large luteal cells (48). Furthermore, progesterone secretion seems to be regulated by cAMP in small but not large ovine luteal cells (81). Journal of Dairy Science Vol. 69, No. 3, 1986 9 2 0 SMITH 4 Alila, H. W., and W. Hansel. 1984. Origin of different cell types in the bovine corpus lu teum as characterized by specific monoclonal anti- bodies. Biol. Reprod. 31:1015. 5 Amann , R. P., and B. D. Schanbacher. 1983. Physiology of male reproduction. J. Anim. Sci. 57 (Suppl. 2):380. 6 Andersen, R. N., F. L. Schwartz, and L. C. Ulberg. 1974. Adenyla te cyclase activity of porcine corpora lutea. Biol. Reprod. 10:321. 7 Anderson, L. L. 1982. Relaxin localization in porcine and bovine ovaries by assay and mor- phologic techniques. Adv. Exp. Med. Biol. 143:1. 8 Anderson, M., J. A. Long, and T. Hayashida. 1975. Immunof luorescence studies on the localization of relaxin in the corpus lu teum of the pregnant rat. Biol. Reprod. 13:499. 9 Anderson, M. B., O. D. Sherwood, and S. J. Downing. 1984. Ultrastructural evaluation of LH induced release of relaxin f rom rat corpora lutea. Biol. Reprod. 30 (Suppl. 1):117. 10 Anderson, M. B., M. R. Vaupel, and O. D. Sher- wood. 1984. Pregnant mouse corpora lutea: immunocytochemica l localization of relaxin and uhras t ructure . Biol. Reprod. 31 : 391. 11 Anderson, W., Y. Kang, M. E. Perotti, T. A. Brameley, and R. J. Ryan. 1979. Interactions of gonadotropins with corpus lu teum membranes . 111. Electron microscopic localization of [~2s I] - hCG binding to sensitive and desensitized ovaries seven days after PMSG-hCG. Biol. Reprod. 20:362. 12 Armstrong, D. T., and W. Hansel. 1959. Alterat ion of the bovine estrous cycle with oxytocin. J. Dairy Sci. 42:533. 13 Balmaceda, J, P., M. R. Borghi, D. H. Coy, A. V. Schally, and R. H. Asch. 1983. Suppression o f postovulatory gonadotropin levels does not affect corpus lu teum funct ion in rhesus monkeys . J. Clin. Endocrinol. Metab. 57:866. 14 Barano, J.L.S., and J. M. Hammond . 1985. Sites of action of FSH or progesterone secretion by immature granulosa cells maintained in serum-free conditions. Page 345 in Proc. 5th Ovarian Work- shop. D. O. Tof t and R. J. Ryan, ed. Ovarian Workshops, Champaign, IL. 15 Bassett, D. L. 1943. The changes in the vascular pat tern of the ovary o f the albino rat during the estrous cycle. Am. J. Anat. 73:251. 16 Bazer, F. W., and N. L. First. 1983. Pregnancy and parturi t ion. J. Anita. Sci. 57 (Suppl. 2):425. 17 Behrman, H. R., J. L. Luborsky-Moore, C. Y. Pang, K. Wright, and J. L. Dorflinger. 1979. Mechanisms of PGF2c ~ action in funcional luteolysis. Adv. Exp. Med. Biol. 112:557. 18 Britt, J. H. 1979. Prospects for controlling reproductive processes in cattle, sheep and swine from recent findings in reproduction. J. Dairy Sci. 62:651. 19 Bryant-Greenwood, G. D. 1982. Relaxin as a new hormone. Endocr. Rev. 3:62. 20 Caffrey, J. L., T. M. Nett, J. H. Abel, Jr., and G. D. Niswender. 1979. Activity of 3/3-hydroxy-~X5- steroid dehydrogenase/ZkS-Z~4-isomerase in the ovine corpus luteum. Biol. Reprod. 20:279. Journal of Dairy Science Vol. 69, No. 3, 1986 21 Cameron, J. L., and R. L. Stouffer. 1982. Gonad- otropin receptors of the primate corpus lu teum. II. Changes in available luteinizing ho rmone and chorionic gonadotropin binding sites in macaque luteal membranes during the nonfert i le menstrual cycle. Endocrinology 110:2068. 22 Channing, C. P. 1970. Influence of the in vivo and in vitro hormonal envi ronment upon luteini- zat ion of the granulosa cells in tissue culture. Recent Prog. Horm. Res. 26:589. 23 Clark, M. R., Y. Kawai, J. S. Davis, and W. J. LeMarie. 1985. Ovarian protein kinases. Page 383 in 5th Ovarian Workshop. D. O. Tof t and R. J. Ryan, ed. Ovarian Workshops, Champaign, 1L. 24 Coleman, D. A., and R. A. Dailey. 1983. Effects o f repeated removal o f large ovarian follicles and t rea tment with progestin on ovarian funct ion in the ewe. Biol. Reprod. 29:586. 25 Cooke, R. G., and A. Knif ton. 1981. Oxytocin- induced oestrus in the goat. Theriogenology 16:95. 26 Corner, G. W. 1919. On the origin of the corpus lu teum of the sow from both granulosa and theca interna. Am. J. Anat. 26:117. 27 Corner, G. W., Jr. 1956. The histological dating of the human corpus lu teum of menst ruat ion. Am. J. Anat. 98:377. 28 Crisp, T. M., and D. A. Dessouky. 1980. Fine structure of the primate corpus luteum. Page 150 in Biology of the ovary. P. M. Motta and E.S.E. Hafez, ed. Martinus Nijhoff Publ., Lond. 29 Crisp, T. M., D. A. Dessouky, and F. R. Denys. 1970. The fine s tructure o f the human corpus lu teum of early pregnancy and during the pro- gestational phase o f the menstrual cycle. Am. J. Anat. 127:37. 30 Darbon, J. M., J. Ursely, and P. LeMarie. 1976. Stimulation by LH of cyclic AMP-dependent protein kinase activity in bovine corpus lu teum slices. FEBS Lett. 63:159. 31 Davis, J. S. 1985. Protein kinase activity and phospholipid metabol ism in rat corpora lutea during pseudopregnancy. Page 409 in 5th Ovarian Workshop. D. O. Toft and R. J. Ryan, ed. Cham- paign, IL. 32 Davis, J. S., and M. R. Clark. 1983. Activation of protein kinase in the bovine corpus lu teum by phospholipid and Ca 2+. Biochem. J. 214:569. 33 Davis, J. S., R. V. Farese, and J. M. Marsh. 1981. Stimulation of phospholipid labeling and steroido- genesis by Iuteinizing ho rmone in isolated bovine luteal cells. Endocrinology 109:469. 34 Diekman, M. A., P. O. Callahan, T. M. Nett, and G. D. Niswender. 1978. Validation of me thods and quantif icat ion of luteal receptors for LH throughout the estrous cycle and early pregnancy in ewes. Biol. Reprod. 19:999. 35 diZerega, G. S., and G. D. Hodgen. 1981. Luteal phase dysfunct ion infertility: A sequel to aberrant fooliculogenesis. Fertil. Steril. 35:489. 36 Donaldson, L., and W. Hansel. 1965. Histological s tudy of bovine corpora lutea. J. Dairy Sci. 48:905. 37 Donaldson, L. E., and W. Hansel. 1965. Pro- longation o f life span o f the bovine corpus SYMPOSIUM: OVARIAN FUNCTION 921 luteum by single injections of bovine luteinizing hormone. J. Dairy Sci. 48:903. 38 Dufau, M. L., and K. J. Catt. 1978. Gonadotropin receptors and regulation of steroidogenesis in the testis and ovary. Vitam. Horm. 36:461. 39 Ellinwood, W. E., T. M. Nett, and G. D. Niswender. 1978. Ovarian vasculature: Structure and func- tion. Page 583 in The vertebrate ovary. R. E. Jones, ed. Plenum Press, New York, NY. 40 Enders, A. C. 1973. Cytology of the corpus luteum. Biol. Reprod. 8:158. 41 Evans, G., M. Dobias, G. J. King, and D. T. Armstrong. 1981. Estrogen, androgen and progesterone biosynthesis by theca and granulosa of preovulatory follicles in the pig. Biol. Reprod. 25:673. 42 Fairclough, R. J., L. G. Moore, L. T. McGowan, A. T. Peterson, J. F. Smith, H. R. Trevit, and W. B. Watkins. 1980. Temporal relationship between plasma concentrations of 13, 14-dihydro-15- keto-prostaglandin F and neurophysin l/II around luteolysis in sheep. Prostaglandins 20:199. 43 Farese, R. V. 1983. Phosphoinositide metabolism and hormone action. Endocr. Rev. 4:78. 44 Farin, C. E., R. H. Schwall, F. Gamboni, H. R. Sawyer, and G. D. Niswender. 1985. Effect of LH and hCG on size distributions of luteal cells in the cycling ewe. Biol. Reprod. 32 (Suppl. 1):44. 45 Fields, M. J., P. A. Fields, A. Castro-Hernandez, and L. H. Larkin. 1980. Evidence for relaxin in corpora lutea of late pregnant cows. Endo- crinology 107:869. 46 Fields, P. A., R. K. Eldridge, A. Fuchs, R. F. Roberts, and M. J. Fields. 1983. Human placental and bovine corpora lutea oxytocin. Endocrinology 112:1544. 47 Fitz, T. A., J. L. Fleeger, M. F. Smith, and P. G. Harms. 1980. Human chorionic gonadotropin (hCG) binding and adenylate cyclase (AC) activity in developing and regressing corpora lutea (CL). Biol. Reprod. 22 (Suppl. 1):61A. 48 Fitz, T. A., M. H. Mayan, H. R. Sawyer, and G. D. Niswender. 1982. Characterization of two steroidogenic cell types in the ovine corpus luteum. Biol. Reprod. 27:703. 49 Fitz, T. A., E. J. Mock, M. H. Mayan, and G. D. Niswender. 1984. Interactions of prostaglandins with subpopulations of ovine luteal cells. II. Inhibitory effects of PGF2~ and protection by PGE ~. Prostaglandins 28:127. 50 Fletcher, P. W., and G. D. Niswender. 1982. Effect o f PGF2a on progesterone secretion and adenylate cyclase activity in ovine luteal tissue. Prostaglandins 23:803. 51 Flint, A.P.F., and E. L. Sheldrick. 1982. Ovarian secretion of oxytocin is stimulated by pro- staglandin. Nature 297 : 587. 52 Flint, A.P.F., and E. L. Sheldrick. 1983. Evidence for a systemic role for ovarian oxytocin in luteal regression in sheep. J. Reprod. Fertil. 67:215. 53 Flint, A.P.F., E. L. Sheldrick, W. B. Watkins, and L. G. Moore. 1984. Ovarian secretion of neuro- physins. Page 15 in Proc. Soc. Study Fertil. Annu. Mtg. 54 Foley, R. C., and J. S. Greenstein. 1958. Cy- tological changes in the bovine corpus luteUm during early pregnancy. Page 88 in Reproduction and infertility. F. X. Gassner, ed. Pergammon Press, New York, NY. 55 Garverick, H. A., M. F. Smith, R. G. Elmore, G. L. Morehouse, L. S. Agudo, and W. L. Zahler. 1985. Changes and interrelationships among luteal LH receptors, adenylate cyclase activity and phosphodiesterase activity during the bovine estrous cycle. J. Anim. Sci. 61:216. 56 Gemmell, R. T., and B. D. Stacy. 1977. Effects o f colchicine on the ovine corpus luteum: role of microtubules in the secretion of progesterone. J. Reprod. Fertil. 49:115. 57 Gemmell, R., and B. D. Stacy. 1979. Ultra- structural study of granules in the corpora lutea of several mammalian species. Am. J. Anat. 155:1. 58 Gemmell, R. T., and B. D. Stacy. 1979. Effect of cycloheximide on the ovine corpus luteum: The role of granules in the secretion of progesterone. J. Reprod. Fertil. 57:87. 59 Gemmell, R. T., B. D. Stacy, and G. D. Thorburn. 1974. Uhrastructural study of secretory granules in the corpus luteum of the sheep during the estrous cycle. Biol. Reprod. 11:447. 60 Gemmell, R. T., B. D. Stacy, and G. D. Thorburn. 1976. Morphology of the regressing corpus luteum in the ewe. Biol. Reprod. 14:270. 61 Goldenberg, R. L., W. E. Bridson, and P. O. Kohler. 1972. Estrogen stimulation of pro- gesterone synthesis by porcine granulosa cells in culture. Biochem. Biophys. Res. Comrnun. 48:101. 62 Goodman, A. L., and G. D. Hodgen. 1979. Between-ovary interaction in the regulation of follicle growth, corpus luteum function, and gonadotropin secretion in the primate Ovarian cycle. II. Effects of luteectomy and hemi- ovariectomy during the luteal phase in cy- nomolgus monkeys. Endocrinology 104:1310. 63 Goodman, A. L., and G. D. Hodgen. 1982. Antifolliculogenic action of progesterone despite hypersecretion of FSH in monkeys. Am. J. Physiol. Endocrinol. Metab. 243 :E387. 64 Goodman, A. L., W. E. Nixon, and G. D. Hodgen. 1979. Between-ovary interaction in the regulation of follicle growth, corpus luteum function, and gonadotropin secretion in the primate ovarian cycle. III. Temporal and spatial dissociation of folliculogenesis and negative feedback regulation o f tonic gonadotropin release after luteectomy in rhesus monkeys. Endocrinology 105:69. 65 Gospodarowicy, D., and K. K. Thakral. 1978. Production of a corpus luteum angiogenic factor responsible for proliferation of capillaries and neovascularization of the corpus luteum. Proc. Natl. Acad. Sci. 75:847. 66 Hanciko, T., and J. Kolena. 1975. Production of oestradiol, cAMP, 12s Ih'CG binding by rat ovaries during the reproductive cycle. Endokrinologie 66:15. 67 Hansel, W. 1971. Survival and gonadotropic responsiveness of luteal cells in vitro. Page 295 in Journal o f Dairy Science Vol. 69, No. 3, 1986 9 2 2 SMITH Research me thods in reproductive endocrinology: in vitro me thods in reproductive ceil biology. A. Disfalusy, ed. Karolinska Syrup., Stockholm. 68 Hansel, W., P. W. Concannon, and J. H. Luk- aszewska. 1973. Corpora lutea of the large domest ic animals. Biol. Reprod. 8:222. 69 Hansel, W., and E. M. Convey. Physiology of the estrous cycle. J. Anita. Sci. 57 (Suppl. 2):404. 70 Hansel, W., and J. Fortune. 1978. The applica- t ions of ovulat ion control. Page 237 in Control of ovulation. D. B. Crighton, N. B. Haynes, G. R. Foxcroft , and G. E. Lamming, ed. Butterworths, Lond. 71 Hansel, W., and W. C. Wagner. 1960. Luteal inhibition in the bovine as a result of oxytoc in injections, uter ine dilatation and intrauterine infusions of seminal and preputial fluids. J. Dairy Sci. 43:796. 72 Haresign, W., J. P. Foster, N. B. Haynes, D. B. Crighton, and G. E. Lamming. 1975. Progesterone levels following t rea tment of seasonally anoestrus ewes with synthet ic LH-releasing hormone. J. Reprod. Fertil. 43:269. 73 Healy, D. L., R. S. Schenken, A. Lynch, R. F. Williams, and G. D. Hodgen. 1984. Pulsatile progesterone secretion: its relevance to clinical evaluation of corpus lu teum function. Fertil. Steril. 41:114. 74 Heath, E., P. Weinstein, B. Merritt, R. Shanks, and J. Hixon. 1983. Effects of prostaglandins on the bovine corpus lu teum: granules, lipid in- clusions, and progesterone secretion. Biol. Reprod. 29:977. 75 Heder, G., W. Jakob, W. Hzlle, B. Mauersberger, G. Kambach, K. D. Jentzsch, and P. Oehme. 1979. Influence of porcine corpus lu teum extract on DNA synthesis and proliferation of cultivated fibroblasts and endothelial cells. Exp. Pathol. 17:493. 76 Higuchi, T., A. Kaneko, J. H. Abel, Jr., and G. D. Niswender. 1976. Relationship between mem- brane potential and progesterone release in ovine corpora lutea. Endocrinology 99:1023. 77 Hirata, F., and J. Axelrod. 1980. Phospholipid methyla t ion and biological signal transmission. Science 209:1082. 78 Hirata, F., W. J. S tu t tmat ter , and J. Axelrod. 1979. /3-Adrenergic receptor agonists increase phospholipid methylat ion, membrane fluidity, and /3 adrenergic receptor-adenylate cyclase coupling. Proc. Natl. Acad. Sci. 76:368. 79 Hixon, J. E., and W. Hansel. 1979. Effects o f prostaglandin F2c~, estradiol, and luteinizing ho rmone in dispersed cell preparation of bovine corpora lutea. Adv. Exp. Med. Biol. 112:613. 80 Hixon, J. E., G. J. Pijanowski, P. G. Weston, R. D. Shanks, and W. C. Wagner. 1983. Evidence for an oscillator o ther than luteinizing ho rmone controlling the secretion o f progesterone in cattle. Biol. Reprod. 29:1155. 81 Hoyer, P. B., T. A. Fitz, and G. D. Niswender. 1984. Hormone- independent activation of ad- enylate cyclase in large steriodogenic ovine luteal cells does not result in increased progesterone secretion. Endocrinology 114:604. 82 Hsueh, A.J.W., E. Y. Adashi, P.B.C. Jones, and T. H. Welsh. 1984. Hormonal regulation of the differentiation o f cultured ovarian granulosa cells. Endocr. Rev. 5:76. 83 Hunter, R.H.F. 1980. Techniques for modif icat ion o f the oestrus cycle: Synchronizat ion o f oestrus and programmed breeding. Page 35 in Physiology and technology of reproduct ion in female do- mestic animals. Academic Press, Lond. 84 Hunzicker-Dunn, M., and L. Birnbaumer. 1976. Adenylyl cyclase activities in ovarian tissues. Ill. Regulation of responsiveness to LH, FSH, and PGE 1 in the prepubertal , cycling, pregnant, and pseudopregnant rat. Endocrinology 99:198. 85 Hunzicker-Dunn, M., and L. Birnbaumer. 1976. Adenylyl cyclase activities in ovarian tissues. If. Regulation of responsiveness to LH, FSH, and PGEI in the rabbit. Endocrinology 99:185. 86 Inskeep, E. K., and W. J. Murdoch. 1980. Relation of ovarian funct ions to uterine and ovarian secretion of prostaglandins during the estrous cycle and early pregnancy in the ewe and cow. Page 325 in Reproductive physiology. Ill. Inter- national review of physiology. R. O. Greep, ed. Vol. 22. Univ. Park Press, Baltimore, MD. 87 lvell, R., and D. Richter. 1984. The gene for the hypotha lmic peptide ho rmone oxytoc in is highly expressed in the bovine corpus lu teum: Bio- synthesis, structure, and sequence analysis. Eur. Mol. Biol. Org. J. 3:2351. 88 Jakob, W., K. D. Jentzsch, B. Mauersbergr, and P. Oehme. 1977. Demonst ra t ion of angiogenesis activity in the corpus lu teum of cattle. Exp. Pathol. 13:231. 89 Karsch, F. J., S. J. Legan, K. D. Ryan, and D. L. Foster. 1980. Impor tance of estradiol and progesterone in regulating LH secretion and estrous behavior during the sheep estrous cycle. Biol. Reprod. 23:404. 90 Kawai, Y., M. R. Clark, and W. J. LeMarie. 1985. The effects of phorbol esters in Ca 2 + and lipid dependent protein kinase activity in the h u m a n corpus luteum. Page 437 in 5th Ovarian Workshop. D. O. Toft and R. J. Ryan, ed. Champaign, IL. 91 Kendall, J. Z., C. G. Plopper, and G. D. Bryant- Greenwood. 1978. Ultrastructural immuno- peroxidase demonst ra t ion of relaxin in the corpora lutea f rom a pregnant sow. Biol. Reprod. 18:94. 92 Koos, R. D., and W. Hansel. 1981. The large and small cells of the bovine corpus lu teum: Ultra- structural and functional differences. Page 197 in Dynamics of ovarian function. N. B. Schwartz and M. Hunzicker-Dunn, ed. Raven Press, New York, NY. 93 Koos, R. D., and W. J. LeMarie. 1983. Factors that may regulate the growth and regression of blood vessels in the ovary. Sere. Reprod. Endo- crinol. 1:295. 94 Koos, R. R., and W. J. LeMarie. 1983. Evidence for an angiogenic factor f rom rat follicles. Page 191 in Factors regulating ovarian function. G. S. Greenwald and P. F. Terranova, ed. Raven Press, New York, NY. 95 Krzymowski, T., J. Kotwica, S. Okrasa, T. Journal o f Dairy Science Vol. 69, No. 3, 1986 SYMPOSIUM: OVARIAN FUNCTION 925 neurophys in in ovine corpora tutea. Biol. Reprod. 32(Suppl. 1):93. 159 Schallenberger, E., J. Rampp, and D. L. Walters. 1983. Pulsatile progesterone secretion occurs during midgestat ion in the cow even though pulsatile LH secretion is abolished. J. Anim. Sci. 57 (Suppl. 1):371. (Abstr.) 160 Schallenberger, E., D. Schams, B. Bullerman, and D. L. Walters. 1984. Pulsatile secretion o f go- nadotropins, ovarian steroids, and ovarian oxy- tocin during prostaglandin-induced regression of the corpus lu teum in the cow. J. Reprod. Fertil. 71:493. 161 Schams, D., A. Lahlow-Kassi, and P. Glatzel. 1982. Oxytoc in concentrat ions in peripheral blood during the oestrous cycle and after ovar- iectomy in two breeds o f sheep with low and high fecundity. J. Endocrinol. 92:9. 162 Schams, D., A. Prokopp, and B. Schmidt- Adamopoulow. 1982. The effect o f active immuniza t ion against oxytoc in on ovarian cyclicity in ewes. Aeta Endocrinol. Suppl.:7. (Abstr.) 163 Schomberg, D. W., S. P. Condert, and R. V. Short. 1967. Effects of bovine luteinizing hor- mone and h u m a n chorionic gonadotropin on bovine cropus lu teum in vivo. J. Reprod. Fertil. 14:277. 164 Schwabe, C., B. Steinetz, G. Weiss, A. Segaloff, J. K. McDonald, E. O'Byrne, J. Hochman, B. Carriere, and L. Goldsmith. 1978. Relaxin. Recent Prog. Horm. Res. 34:123. 165 Sernia, C., G. D. Thorburn , and R. T. Gemmell. 1982. Search for a progesterone-binding protein in secretory granules of the ovinc corpus lu teum. Endocrinology 110:2151. 166 Sheldrick, E. L., and A.P.F. Flint. 1983. Re- gression of the corpora lutea in sheep in response to cloprostenol is no t affected by loss of luteal oxytoc in after hys terec tomy. J. Reprod. Fertil. 68:155. 167 Sheldrick, E. L., and A.P.F. Flint. 1983. Luteal concentrat ions of oxytocin decline during early pregnancy in the ewe. J. Reprod. Fertil. 68:477. 168 Sheldrick, E. L., and A.P.F. Flint. 1984. Ovarian oxytoc in and luteal funct ion in the early pregnant sheep. Anita. Reprod. Sci. 7:101. 169 Sheldrick, E. L., M. D. Mitchell, and A.P.F. Flint. 1980. Delayed luteal regression in ewes immunized against oxytocin. J. Reprod. Fertil. 59:37. 170 Sherman, B. M., and S. G. Korenman. 1974. Measurement o f plasma LH, FSH, estradiol and progesterone in disorders of the h u m a n menstrual cycle: The short luteal phase. J. Clin. Endocrinol. Metab. 38:89. 171 Singer, S. J., and G. L. Nicolson. 1972. The fluid mosiac model of the s tructure of cell membranes . Science 175:720. 172 Sinha, A. A., U. S. Seal, and R. P. Doe. 1971. Ultrastructure of the corpus lu teum of the white-tailed deer during pregnancy. Am. J. Anat. 132:189. 173 Snook, R. B., M. A. Brunner. R. R. Saatman, and W. Hansel. 1969. The effect of antisera to bovine LH in hys terec tomized and intact heifers. Biol. Reprod. 1:49. 174 Sopelak, V. M., and G. D. Hodgen. 1984. Transi- tory increases of luteinizing ho rmone and follicle- s t imulat ing ho rmone following lu teec tomy in hemiovariectomized primates significantly in- creases progesterone secretion in vitro by the subsequent corpus luteum. Biol. Reprod. 31 : 132. 175 Spicer, L. J., J. J. lreland, and J. F. Roche. 1981. Changes in serum LH, progesterone and specific binding of [12sI]-HCG to luteal cells during regression and development of bovine corpora lutea. Biol. Reprod. 25:832. 176 Spiegel, A. M., and R. W. Downs, Jr. 1981. Guanine nucelotides: Key regulators of hormone receptor-adenylate cyclase interaction. Endocr. Rev. 2. 177 Stansfield, D. A., D. J. Franks, G. H. Wilkinson, and J. R. Hone. 1972. Studies on the format ion and degradation of adenosine 3', 5' cyclic mono- phosphate in the corpus luteum. J. Ster. Biochem. 3:643. 178 Stouffer, R. L., J. L. Coensgen, G. S. di Zerega and G. D. Hodgen. 1981. Induct ion of defective corpus lu teum funct ion by adminis t ra t ion of follicular fluid to monkeys during the follicular phase of the menstrual cycle. Page 185 in Dy- namics of ovarian function. N. B. Schwartz and M. Hunzicker-Dunn, ed. Raven Press, New York, NY. 179 Streb, H., R. F. Irvine, M. J. Berridge, and I. Schulz. 1983. Release of Ca 2+ from a non- mitochondrial intracellular store in pancreatic acinar cells by inositol-1, 4, 5-triphosphate. Nature 306:67. 180 Strott , C. A., C. M. Cargille, G. T. Ross, and M. B. Lipsett. 1970. The short luteal phase. J. Clin. Endocrinol. 30:246. 181 Sun, F. F., J. P. Chapman, and J. C. McGuire. 1977. Metabolism of prostaglandin endoperoxide in animal tissues. Prostaglandin 14:1055. 182 Suter, D. E., P. W. Fletcher, P. M. Sluss, L. E. Reichert, Jr., and G. D. Niswender. 1980. Alter- ations in the number o f ovine luteal receptors for LH and progesterone secretion induced by homologous hormone . Biol. Repro& 22:205. 183 Tan, G. S., and J.S.G. Briggs. 1984. Progesterone product ion by dispersed luteal cells of non- pregnant cows: Effects of oxytoc in and oestradiol. Anim. Repro& Sci. 7:441. 184 Tan, G.J.S., R. Tweedale, and J.S.G. Briggs. 1982. Effects o f oxytoc in on the bovine corpus lu teum of early pregnancy. J. Reprod. Fertil. 66:75. 185 Thanki, K. H., and C. P. Channing. 1978. Effect of FSH and estradiol upon progesterone secretion by porcine granulosa cells in tissue culture. Endocrinology 103:74. 186 Thompson , W. J., and S. J. Strada. 1978. Hor- monal regulation of cyclic nucleotide phos- phodiesterase. Page 535 in Receptors and hor- mone action. B. W. O'Malley and L. Birnbanmer, ed. Vol. llI. Academic Press, New York, NY. 187 TroxeI, T. R., and D. J. Kesler. 1983. Progestin pre t rea tment enhances the func t ion of corpora lutea induced by gonadotropin releasing ho rmone Journal of Dairy Science Vol. 69, No. 3, 1986 926 SMITH t rea tment in pos tpar tum suckled beef cows. J. Anim. Sci. 57 (Suppl. 1):107. 188 Urseley, J., and P. Leymarie. 1979. Varying response to luteinizing ho rmone of two luteal cell types isolated from bovine corpus tu teum. J. Endocrinol. 83 : 303. 189 Veldhuis, J. D., and P. A. Klase. 1983. Calcium ions modula te hormonal ly s t imulated pro- gesterone product ion in isolated ovarian cells. Biochem. J. 202:381. 190 Veldhuis, J. D., and P. A. Klase. 1982. Mech- anisms by which calcium ions regulate the steroidogenic actions of luteinizing hormone in isolated ovarian cells in vitro. Endocrinology 111:1. 191 Walters, D. L., D. Schams, and E. Schallenberger. 1984. Pulsatile secretion o f gonadotrophins , ovarian steroids and ovarian oxytoc in during the luteal phase of the oestrous cycle in the cow. J. Reprod. Fertil. 71 ;479. 192 Warbritton, V. 1934. The cy to logyof the corpora lutea of the ewe. J. Morphol. 56:181. 193 Wathes, D. C., and R. W. Swann. 1982. Is oxytoc in an ovarian hormone? Nature 297:225. 194 Wathes, D. C., R. W. Swann, S. D. Birkett, D. G. Porter, and B. T. Pickering. 1983. Characterization of oxytoc in , vasopressin and neurophysin from the bovine corpus luteum. Endocrinology 113: 693. 195 Wells, J. N., and J. G. Hardman. 1977. Cyclic nucleotide phosphodiesterases. Page 119 in Advances in cyclic nucleotide research. P. Green- gard and G. A. Robison, ed. Raven Press, New York, NY. 196 Wilkinson, R. F., E. Anderson, and J. Aalberg. 1976. Cytological observations of dissociated rat corpus luteum. J. Ultrastruct. Res. 57:168. 197 Wilks, J. W., G. D. Hodgen, and G. T. Ross. 1976. Luteal phase defects in the rhesus monkeys : The significance of serum FSH:LH ratio. J. Clin. Endocrinol. Metab. 43 : 1261. 198 Willcox, D. L., G. Jenkin, S. J. Quirk, and G. D. Thorburn. 1979. Progesterone binding protein in the bovine corpus luteum. J. Endocrinol. 80:13. 199 Zeleznik, A.J . , H. M. Schuler, and L. E. Reichert, Jr. 1981. Gonadotropin-binding sites in the rhesus monkey ovary: Role of the vasculature in the selective distr ibution of h u m a n chorionic gonadotropin in the preovulatory follicle. En- docrinology 109:356. 200 Zor, U. 1983. Role o f cytoskeleton organization in the regulation of adenylate cyclase-cyclic adenosine monophospha t e by hormones . Endocr. Rev. 4:1. Journal of Dairy Science Vol. 69, No. 3, 1986