Presence Of Gonadotropin Research Articles

In VitroEffects of Follicle-Stimulating Hormone, Luteinizing Hormone, and Prolactin on Follicular Deoxyribonucleic Acid Synthesis in the Hamster*

Follicles were dissected by hand or enzymatically from the ovary of the proestrous hamster at 0900 h and classified into 10 stages: stages 1-4, follicles with 1-4 layers of granulosa cells and no theca; stages 5-8, preantral follicles with 5 or more layers of granulosa cells and theca to small antral follicles; stage 9, intermediate-sized atretic antral follicles; and stage 10, healthy preovulatory antral follicles. Follicles were then incubated for 2 h with [3H]thymidine [( 3H]Tdr) in the absence or presence of gonadotropins and with incorporation of radionuclide into DNA as the end point. FSH (25 ng) significantly stimulated [3H]Tdr incorporation in all stages of follicular development with a latency of 2 h, and this effect was inhibited by 2 micrograms unlabeled Tdr. While FSH and PRL (25 and 100 ng) stimulated [3H]Tdr incorporation in all stages, LH (0.2-5 ng) action began from stage 5 onward, when definitive thecal cells and LH receptors started appearing. LH (5 ng) also suppressed 25 ng FSH-induced DNA synthesis in stages 5-10; however, stages 1-4 were unaffected. Significant increases in both intra- and extracellular cAMP levels occurred in follicles at stages 2-10 after FSH administration. In contrast, LH was active in stages 5-10, whereas PRL was ineffective. Follicular DNA synthesis increased markedly when stimulated by 8-bromo-cAMP (0.01-2 mM). These results show that gonadotropins act directly as a primary stimulus at the level of small primary and secondary follicles to regulate DNA synthesis and, thus, perhaps the growth and differentiation of granulosa and thecal cells; cAMP functions as one of the possible intracellular mediators of gonadotropin action in initiating DNA replication.

Metabolism of 7,12-dimethylbenz(a)anthracene by different types of cells in the human ovary.

1. The metabolism of 7,12-dimethylbenz(a)anthracene (DMBA) by primary cultures of human ovarian cells has been studied to identify the cell type(s) responsible for biotransformation of this carcinogen. The rate of DMBA metabolism was maximal in granulosa cells prestimulated in vivo with antiestrogen, hMG (human menopausal gonadotropin) and hCG (human chorionic gonadotropin), i.e., treatments required for maximal oocyte maturation and, thus, granulosa cell proliferation. In cells from unstimulated ovaries, the metabolism was maximal in granulosa-lutein cells isolated from corpus luteum. 2. Steroid (progesterone and estradiol) levels were determined in the spent culture media or in media in parallel with DMBA metabolism to find out whether elevated steroid levels in vivo are required for the rapid metabolism of DMBA. In granulosa cell cultures from stimulated cycles, the concentrations of both progesterone and estradiol were at least 2 or 3 times higher, respectively, than in any of the other cell types tested. In cell cultures derived from unstimulated ovaries, the progesterone and estradiol concentrations were highest in granulosa-lutein cell cultures. 3. Incubations of granulosa cells with DMBA in the absence or presence of gonadotropins, testosterone or anti--hCG were performed to investigate possible hormonal requirements for the cytochrome P-450 system(s) which metabolize DMBA. No change in the rate of metabolism was obtained with follicle stimulating hormone (FSH), luteinizing hormone (LH), hCG or testosterone. However, anti-hCG increased this activity about 70%, indicating a negative modulatory role of hCG on DMBA mono-oxygenase activity in human granulosa cells. 4. DMBA mono-oxygenase activity in cell cultures was inhibited about 95% by alpha-naphthoflavone (ANF), an inhibitor of certain cytochrome P-450-catalysed activities. Benzo(a)pyrene (BP) was metabolized at the same rate as DMBA in granulosa cell cultures.

A postulated role for naturally occurring aromatase inhibitors in follicle selection

The studies reviewed here indicate that follicle regulatory protein (FRP) alters aromatase and 3B-hydroxysteroid dehydrogenase activity in porcine, human, and rat granulosa cells. The inhibitory effect of FRP on granulosal aromatase activity depend upon the response of the cell to FSH: large amounts of FSH can partially overcome FRP inhibition while relatively small amounts of FSH sensitize the granulosal aromatase system to FRP. Although androgens potentiate FSH-mediated granulosal functions, they also sensitize granulosa cell steroidogenic enzymes to inhibition by FRP. The demonstration that FRP acts primarily on granulosa cells of less mature antral follicles to inhibit aromatase supports the hypothesis that FRP may facilitate follicle selection and suggests a role for FRP in atresia. Most of the effects of FRP on granulosal activities reflect an interplay between the systemic endocrine and local paracrine systems. That FRP functions, at least in part, by modulating follicular response to FSH is consistent with the hypothesis that paracrine effectors are important mediators of folliculogenesis in the presence of gonadotropins.

Ovarian tumors not induced by irradiation and gonadotropins in hypogonadal (hpg) mice.

Hypogonadal (hpg/hpg) mice deficient in gonadotropin-releasing hormone were used to study gonadotropin involvement in ovarian tumorigenesis following gamma irradiation. In the first experiment, 30-day-old hpg/hpg and normal (+/-) littermate mice were irradiated. The same mice were killed 10-15 mo later, and autopsies were performed. Ovaries of irradiated hpg/hpg mice were devoid of oocytes, but retained follicular structures. Neither mesothelial adenomas nor granulosa cell tumors were observed. In contrast, all irradiated +/- mice formed mesothelial adenomas or granulosa cell tumors, or both. Therefore, oocyte death in the absence of gonadotropins did not initiate ovarian tumorigenesis. In the second experiment, irradiated and nonirradiated hpg/hpg and +/- mice were injected 3 times weekly for 180 days with either low or high doses of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) in combination. Irradiation reduced ovarian mass and markedly reduced ovarian weight increase in response to exogenous gonadotropins. Follicular dissolution and stromal cell hypertrophy were observed in saline-treated and gonadotropin-treated +/- mice that had been irradiated, and in hpg/hpg mice given the high gonadotropin dose. Mesothelial adenoma formation was observed in 100% of saline-treated, 14% of low dose-treated, and 11% of high dose-treated +/- mice. No mesothelial adenomas developed in any hpg/hpg or nonirradiated +/- mice, despite gonadotropin-induced stromal luteinization. These results indicate that, in the absence of gonadotropins, irradiation leads only to the loss of oocytes. The presence of gonadotropins was necessary to promote follicular dissolution and stromal luteinization, but was insufficient to stimulate mesothelial adenoma formation.

The course of steroid release by intact ovarian follicles of atlantic salmon ( Salmo salar) incubated in vitro with and without gonadotrophin

Intact ovarian follicles were dissected from a single ovary and groups of follicles incubated in balanced saline at 6° with and without a pacific salmon gonadotrophin (GTH) preparation. Aliquots of the incubation media were withdrawn at intervals, the steroids were extracted with solvent, and 17α, 20β-dihydroxy-4-pregnen-3-one (17α20βP), 17α-hydroxyprogesterone, progesterone, androstenedione, testosterone, and oestradiol were separated chromatographically and measured by radioimmunoassay. The main findings were (1) germinal vesicle breakdown commenced on Day 8 under the influence of GTH, (2) after an induction period of about 2 days there was a dramatic and continuing release of 17α20βP in the presence of GTH, (3) GTH promoted a moderate release of 17α-hydroxyprogesterone, (4) GTH stimulated testosterone release up to Day 6 but thereafter levels fell, reflecting either absorption or catabolism of the released steroid, (5) GTH induced a precipitous release of androstenedione during the first few hours of incubation, and (6) progesterone and oestradiol release were little affected by GTH. Steroid concentrations were also measured in ova stripped from naturally ovulating wild fish and the relative amounts were shown to bear some similarity to those released into the incubation medium in the presence of GTH. The routes of biosynthesis and functions of these steroids are considered in light of the results.

Detection of gonadotrophic hormones on isolated thecal interstitial cells of the domestic hen, Gallus domesticus, by an immunohistochemical method.

An immunohistochemical method was used to demonstrate the presence of gonadotrophins in isolated ovarian interstitial cells. The cells were obtained by collagenase digestion of large ovarian follicles after removal of the yolk and the granulosa layer. Using a peroxidase-labelled anti-rabbit serum with anti-chicken follicle stimulating hormone (FSH) serum raised in rabbits, a strong positive reaction was obtained. Anti-human FSH serum also produced a positive result but the reaction was weaker. There was no apparent difference in the staining reaction of cells which had been preincubated with ovine FSH serum. Treatment with anti-ovine luteinizing hormone (LH) resulted in a faintly positive reaction. The viability of the cells was tested by the Trypan Blue method and they were identified as steroid-producing cells by the histochemical demonstration of their 3 beta-hydroxysteroid dehydrogenase activity.

The effect [formula omitted] of alterations in gonadotropins and cyclic nucleotides on oocyte maturation in the hamster

The temporal relationship of changes in cAMP and cGMP to oocyte maturation was examined in proestrous hamsters (day 4). The first series of experiments showed, in normal cycling hamsters, an increase in cAMP and a decrease in cGMP at 1400 h shortly after the rise in LH with oocyte maturation beginning at 1800 h. When a second group of animals was injected with phenobarbital at 1200 h to block the LH surge, no significant change occurred in either cyclic nucleotide and oocyte maturation was prevented. In the second series of experiments single injections of either saline, hCG (30 IU), LH (10 μg) or FSH (10 μg) were given each to a group of animals at 0900 h on day 4. Animals were killed at five time intervals between 15 min and 3 h following the injection. LH and hCG stimulated a simultaneous increase in cAMP and decline in cGMP. The injection of FSH, however, did not cause an increase in cAMP but still produced a sharp decline in cGMP. Oocyte maturation occurred at 3 h in those animals injected with gonadotropins. Animals injected with saline showed neither cyclic nucleotide changes nor oocyte maturation. When cAMP and cGMP levels were expressed as a ratio (cAMP/cGMP) a significant increase occurred in the normal cycling animals and in those injected at 0900 h with gonadotropins. Phenobarbital and saline injected control animals showed no significant increase in the cAMP/cGMP ratio and no oocyte maturation. The results of these experiments and previous studies by this investigator indicate that cGMP may play an important role in oocyte maturation in the hamster prior to the LH surge. Since, in the presence of gonadotropins, the cAMP/cGMP ratio increases prior to oocyte maturation, it may be that the cyclic nucleotide ratio is also of importance in this process. Previous work by Hubbard and Terranova (1) has shown that guanosine 3′ : 5′ cyclic monophosphate (cGMP) can inhibit spontaneous maturation of hamster oocytes in vitro . This inhibitory action was dose dependent and overcome by LH. The cGMP-mediated inhibition occurred only in cumulus-enclosed oocytes, while adenosine 3′ : 5′ cyclic monophosphate (cAMP) inhibited spontaneous maturation in both cumulus-enclosed and denuded oocytes. The results of this study suggested that cGMP may play a role in inhibiting oocyte maturation prior to the LH surge. LH, the initiator of oocyte maturation, has also been shown in the intact proestrous rat and hamster to cause a decrease in cGMP at the same time that cAMP is rising (2, 3). The effect of these cyclic nucleotide changes on oocyte maturation was not examined. If cGMP is indeed involved in preventing oocyte maturation prior to the LH surge, it is necessary to examine in more detail the relationship of changes in gonadotropins and cyclic nucleotides to oocyte maturation. The purpose of this study, therefore, is to examine the effect of gonadotropins on oocyte maturation and levels of follicular cAMP and cGMP during proestrus in the hamster.

Role of the extra-follicular compartment in the ovulation of isolated rabbit ovarian follicles.

Ovulation was never observed, even in the presence of gonadotrophins, when preovulatory follicles isolated from oestrous does were cultured in vitro (n = 112). If the follicles were co-cultured with pieces of ovarian tissue and gonadotrophins, then 50% ovulated (P less than 0.01). Attempts to replace the ovarian tissue by various steroid hormones or prostaglandins did not result in follicular rupture except when PGE-2 was used (23.8%, P less than 0.05). We suggest that gonadotrophins have an immediate (less than 1 h) action upon the follicle and ovarian interstitial tissue simultaneously. The response of the ovarian tissue to gonadotrophins is essential for eventual follicular rupture and involves PGE-2.

The regulation of LHRH action at the pituitary and gonadal receptor level: A review

Luteinizing hormone releasing-hormone (LHRH) and its highly active agonists are under clinical investigation for the control of reproductive function and for suppression of hormone dependent tumours. The regulation of LHRH action by pituitary receptors and expression of the biological LHRH effect by gonadotropin release and activation of steroid biosynthesis are discussed in this context. Pituitary LHRH receptors are controlled by autoregulation via endogenous LHRH secretion. The gonadal response to LHRH stimulation is regulated by LH action on receptors for LH, prolactin and FSH. Pituitary and gonadal inhibition are achieved by different mechanisms. Continuous exposure to LHRH blocks gonadotropin release and reduces pituitary LH/FSH content, whereas inhibition of steroid biosynthesis requires daily LH release to maintain receptor down-regulation. Pituitary enzymes involved in LHRH degradation at the receptor site are required for terminating hormone action, but their role in modulating hormonal responsiveness is secondary to receptor regulation. Direct gonadal effects of LHRH are exerted in the presence of gonadotropins by modulating the gonadotropin effect, e.g. in hypophysectomized animals. The presence of specific receptors for LHRH agonists in ovarian and testicular tissue suggests local control mechanisms for gonadotropin activation of steroid biosynthesis.

Dissociation of oocyte maturation and ovulation in mice pretreated with a derivative of dihydropyridazinone.

Treatment of mice with a dihydropyridazinone derivative (6-(4'-aminophenyl)-4,5-dihydro-5-methylpyridazin-3-one; ICI 109,081) inhibited the maturation of oocytes in the presence of gonadotrophins without affecting ovulation. The spontaneous resumption of meiosis in oocytes cultured in vitro was reversibly inhibited. ICI 109,081 may therefore be useful for evaluating the relationship between follicular development and the resumption of meiosis.

Cyclic AMP in mammalian follicle cells and oocytes during maturation.

Intact ovarian follicles and isolated oocytes were cultured for 30 sec to 18 hr in the presence of gonadotrophins, and the cyclic AMP content in the follicle and oocyte was measured. The basal content of cyclic AMP in ovine oocytes before gonadotrophic stimulation was 6.3 +/- 0.7 fmol/oocyte or 8 microM. There was no fall in oocyte cyclic AMP concentration as an immediate response to the gonadotrophins, but at 1, and 12-18 hr after stimulation, the concentration in both the oocytes and follicle cells was considerably elevated. There was no comparable increase in intracellular cyclic AMP in oocytes denuded of follicle cells before culture, even when both gonadotrophins and phosphodiesterase inhibitors were included in the medium. We conclude that the signal which initiates oocyte maturation in mammals differs from that of amphibia, where an early fall in intracellular cyclic AMP is essential for the resumption of meiosis. Moreover, cellular interactions within the mammalian follicle are necessary for the characteristic periods of increased cyclic AMP in oocytes during maturation.

Hormone-induced guanyl nucleotide binding and activation of adenylate cyclase in the Leydig cell.

The adenylate cyclase activity of Leydig cell homogenates and membrane fractions is highly dependent on guanyl nucleotides, and enzyme responses to luteinizing hormone or human chorionic gonadotropin are small in the absence of guanyl nucleotides. However, in the presence of 10 microM guanosine 5'-[beta, gamma-imido]triphosphate Gpp[NH]p, both hormones consistently stimulated testicular adenylate cyclase activity by up to 200%. Leydig cell membranes bound [3H]Gpp[NH]p at 30 degrees C with high affinity (Ka = 1.5 X 10(7) M-1) and binding capacity of 60 pmol/mg of protein. During kinetic studies, the association rate constant was 1.7 X 10(6) M-1 min-1, and the dissociation constant was 0.038 min-1. In the presence of gonadotropin (10 pM to 10 nM), concentration-dependent increases of 40% to 100% in Gpp[NH]p binding were observed in Leydig cell membranes. Kinetic studies showed that gonadotropin decreased the association rate constant to 0.73 X 10(6) M-1 min-1 and the dissociation rate constant to 0.017 min-1, with no effect on the equilibrium binding constant. Thus, the increase in Gpp[NH]p binding was not due to a change in receptor affinity but was attributable to increased availability of nucleotide binding sites. The 50% effective dose for adenylate cyclase activation by gonadotropin in the presence of Gpp[NH]p was identical with that observed for gonadotropin-induced binding of the GTP analog (50 nM). Gonadotropin-induced binding of Gpp[NH]p in Leydig cell membranes may represent interaction with the guanyl nucleotide regulatory site during hormonal activation of adenylate cyclase.

Development of the rat oocyte in vitro: Inhibition and induction of maturation in the presence or absence of the cumulus oophorus

The effect in vitro of oocyte maturation inhibitors and the ability of preparations of luteinizing hormone to relieve the arrest induced by these substances was studied in preparations of cumulus-free (naked) rat oocytes, and compared to previously obtained results from oocytes enclosed by their cumulus cells. The development of both the cumulus-oocyte complex and naked oocyte is arrested in vitro by cyclic AMP derivatives or cyclic nucleotide phosphodiesterase inhibitors. While gonadotropins can overcome the effect of these substances in the cumulus oocyte complex, they have no effect on naked oocytes. Cholera enterotoxin, an irreversible activator of adenylate cyclase, maintains developmental arrest in cultured cumulus oocyte complexes but not in naked oocytes. Preparations of luteinizing hormone can partially overcome the effect of cholera enterotoxin in the complexes. Furthermore, the acceleration of oocyte maturation in vitro observed in the presence of gonadotropins, which is seen in cumulus oocyte complexes, can be mimicked by stripping the oocyte of its associated cumulus cells. The results of these and other studies suggest that: (1) the cytoplasmic levels of cyclic AMP in the isolated oocyte are high enough to maintain meiotic arrest if a phosphodiesterase inhibitor is present; (2) the oocyte contains an active phosphodiesterase; (3) the oolemma may lack the adenylate cyclase system and; (4) gonadotropins seem to affect the oocyte indirectly, via the cumulus cells, possibly by interrupting communication between the two cell types.

Cyclic AMP, prostaglandin E2 and steroids: possible mediators in the rat cumulus oophorus mucification.

The possible role of cyclic AMP (cAMP), prostaglandin E2, progesterone and estradiol-17β in in vitro induction of the rat cumulus oophorus mucification was studied with the scanning electron microscope. Follicular cumulus-oocyte complexes were isolated at early proestrus and cultured for 24 h. Cyclic AMP levels in the incubated complexes were elevated by addition of cAMP derivatives (dibutyryl cAMP or 8 bromo cAMP), the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (MIX), or the adenylate cyclase stimulator, cholera enterotoxin. Under all these culture conditions the cumulus cells were stimulated to secrete a hyaluronidase-sensitive mucoid material which coated the cumulus-oocyte complexes. These complexes were similar in appearance to those incubated in the presence of gonadotropins. In the absence of the above agents extracellular material was not observed. In vitro cumulus mucification was not induced by prostaglandin E2; indomethacin, an inhibitor of prostaglandin synthetase, failed to block mucification in complexes that have been incubated in the presence of LH. Cumulus complexes were not stimulated to mucify in vitro by progesterone or estradiol-17β. Therefore, the response of the cumulus cells to the gonadotropic stimulus appears to be mediated by cAMP. Prostaglandin E2 and steroids seem not to be involved in this process.

Studies on oocyte maturation of the medaka, Oryzias latipes. VIII. Role of follicular constituents in gonadotropin‐ and steroid‐induced maturation of oocytes in vitro

AbstractParticipation of the follicular constituents in gonadotropin‐ and steroid‐induced maturation of Oryzias latipes oocytes was examined in vitro by removing these constituents and coculturing them with the denuded oocytes. Removal of all follicular constituents prevented gonadotropin‐induced maturation of oocytes, but the removal of the thecal cells and the basal lamina from the follicle did not prevent maturation. Moreover, the denuded oocytes did mature in the presence of gonadotropin when cocultured with granulosa cells previously separated from large preovulatory follicles or with postovulatory follicles. However, the denuded oocytes did not respond to gonadotropin by maturing when cocultured with either thecal cells and basal lamina of the, premature follicles or the granulosa cells of small follicles 22–24 hr before ovulation. These results indicate that the presence of the granulosa cells of large pre‐ and postovulatory follicles is important for gonadotropin‐induced oocyte maturation. The denuded oocytes, which were incapable of responding to gonadotropin, were stimulated by various steroids to undergo meiotic maturation. The concentrations of steroids effective in inducing maturation were lower for the denuded oocytes than for the oocytes within intact follicles or enveloped by granulosa cells alone.The present results suggest that the gonadotropin‐stimulated granulosa cells of both pre‐ and postovulatory follicles play a major role in inducing oocyte maturation through secretion of steroids in the circadian ovulatory cycle of Oryzias latipes.

Synthesis of Sex Steroids by Cellular Components of Chicken Follicles

The follicular components responsible for the synthesis of progesterone (P), testosterone (T) and estrogen (E) have been identified by studying in vitro the steroidogenic pattern of theca or granulosa cells incubated alone with or without ovine FSH, ovine LH, P or T or incubated together with or without ovine LH. Granulosa cells, but not theca cells, isolated from 3 largest preovulatory and postovulatory follicles produced more P in response to the addition of exogenous gonadotropins. Among the 4 different types of follicles studied, this response of granulosa cells isolated from the largest follicle (F1), the one destined to ovulate next, was the greatest. Both theca and granulosa cells isolated from preovulatory follicles produced 2–3 times more T when incubated in the presence of gonadotropins. Only theca cells from the second (F2) and third (F3) largest follicles synthesize more E when incubated with gonadotropins. The response of F3 was greater than that of F2. Addition of T to the incubation system elicited E synthesis by theca cells of F2 or F3, but not by granulosa cells of any size follicles. Again, the response of theca cells from F3 was greater than that of F2. Furthermore, the ability of theca cells of F3, isolated at or shortly after the preovulatory in vivo LH surge, to aromatize T to E was significantly lower than that isolated several hours before the LH surge. Combination of the 2 follicular cell types from F3 decreased P, but increased T (9- to 17-fold increase) and E synthesis. Theca cells incubated with exogenous P produced large amounts of T. We concluded that the cellular source for P is the granulosa cell and the source for T and E is the theca cell. Theca cells alone cannot synthesize T or E unless the precursor, P or T, respectively, is added. Both theca and granulosa cells are required for synthesis of T, followed by E. Thus, a 2 cell type model for synthesis of these 2 steroids is proposed. The present study also suggests that the steroidogenic potential of the follicular cells changes during the process of follicular maturation.

Studies on oocyte maturation of the medaka, Oryzias latipes. VI. Relationship between the circadian cycle of oocyte maturation and activity of the pituitary gland.

The relationship between pituitary activity and oocyte maturation was examined in Oryzias latipes (medaka), which has a circadian cycle of oviposition. Throughout the circadian cycle of oviposition, females possessed a population of large oocytes more than 800 micronmeter in diameter that could mature in the presence of gonadotropin. Oocyte maturation was observed in vitro in females hypophysectomized between three and ten hours after the beginning of the light period with the number of maturing oocytes increasing as hypophysectomy was delayed. Although in vivo oocyte maturation was blocked by hypophysectomy within two hours after the beginning of the light period, it was restored by a single injection of synthetic or mammalian pituitary hormones (gonadotropic, corticotropic and thyrotropic hormones) within ten hours after hypophysectomy. Of these pituitary hormones, FSH, LH and TSH could induce in vitro maturation of isolated oocytes. Oocytes matured in vitro in the absence of exogeneous hormones if they were isolated nine or more hours after the onset of light. The present study indicates that the circadian cycle of maturation of Oryzias oocytes is controlled by the release of pituitary hormone between three and nine hours after the beginning of the light period.

TEMPORAL CHANGES IN OVARIAN ORNITHINE DECARBOXYLASE AND CYCLIC AMP IN IMMATURE RATS STIMULATED BY EXOGENOUS OR ENDOGENOUS GONADOTROPHINS

Pregnant mare serum gonadotrophin given intravenously to immature rats caused a maximal (x 70) increase in ornithine decarboxylase activity (ODC) at 3 h; enzyme activity declined to about ten times the control levels by 9 h and a second rise began after about 20 h. Anti-PMSG given 30 min after PMSG reduced the peak response by 70%. Actinomycin D, or cycloheximide, completely prevented an increase in ODC when given with PMSG, but only cycloheximide lowered the enzyme activity when given 18 h later. Ovine FSH plus LH also produced a peak in ODC at 3 h but the activity decreased quickly and by 9 h it was at the control level. Secretion of endogenous FSH and LH, induced by hourly injections of LH releasing hormone (LH-RH) increased ODC to the same extent as did the exogenous hormones; ODC was still higher than in the controls 4 h after the last dose of LH-RH. Increased endogenous levels of FSH and LH did not consistently raise ovarian cyclic AMP content and the increases found were much less than those obtained after injection of PMSG or FSH+LH. The results indicate that increased ODC is induced and maintained by the continual presence of gonadotrophin. The dependence of increased ODC upon increased cyclic AMP cannot be unequivocally determined because of important differences in the timing of the responses and the difficulty in determining biologically significant changes in cyclic AMP.

The Presence of Gonadotropin and Prostaglandin E Receptors in the Cell Membranes of Bovine Corpora Lutea Throughout Pregnancy

These studies revealed that the cell membranes prepared from bovine corpora lutea contain receptors for both human chorionic gonadotropin and prostaglandin E throughout pregnancy. The presence of these receptors correlated well with the earlier findings that the corpus luteum remains functional and responds to gonadotropic stimulation throughout the bovine pregnancy. This contrasts with our earlier findings that human corpora lutea of pregnancy of more than 6 weeks contain very few or no available receptors for human chorionic gonadotropin or prostaglandin E.

Presence of a gonadotrophin on the surface of preimplanted mouse embryos.

IN humans, a gonadotrophin (hCG) is localised on the cell membrane of the syncytiotrophoblast facing the maternal bloodstream1. The syncytiotrophoblast is derived from the trophoblast cells of the mammalian blastocyst and is thought to participate in isolating the foetus from attack by the maternal immunological system2. Martin, et al.1 suggest that the hCG on human syncytial plasma membranes may, in part, be responsible for the lack of maternal immunological rejection of the foetus; in addition to its role in steroidogenesis, therefore, hCG may also have an immunological function during pregnancy. Because hCG is generally used to induce super-ovulation in mice and must, therefore, cross-react with mouse gonadotrophin, and since the mouse is extensively used in studies on mammalian development, I investigated the possible presence of gonadotrophin(s) in mouse embryos before implantation and formation of the syncytiotrophoblast. Using an antiserum to hCG and indirect immunofluorescence (IIF) I have detected a luteinising hormone (LH)- or hCG-like substance (‘embryonic gonadotrophin’, EG) on the cell surfaces, of live mouse preimplanted embryos.