Development of fetal rat ovaries responsiveness to LH during organ culture.

The responsiveness of fetal neonatal rat ovaries to LH was investigated in vitro using three complementary approaches. First, steroid production was assessed after culture. In control media, detectable levels of estrogens (estradiol and estrone) and progesterone were only observed from day 6 postpartum and during the second week of life respectively. In the presence of LH (100 ng/ml) ovaries produced both estrogens and progesterone from day 4 postpartum and the response to LH was enhanced with IBMX supplementation in the medium. Second, 3 beta-HSD activity was measured with either LH or (Bu)2 cAMP (1mM). Irrespective to the time-period studies (Bu)2 cAMP stimulated this enzyme whereas the stimulation with LH occurred only from day 5 postpartum Third, specific hCG binding was assessed and we found that it occurred only on days 7 and 10. However, when fetal ovaries were pretreated for 48 h with (Bu)2 cAMP, a specific hCG binding could be detected and progesterone production was enhanced in response to LH. An effect of the nucleotide via a stimulation of the neuraminidase activity did not seem to be involved. Lastly treatment of 18-day-old fetal ovaries with cholera toxin (10nM) or forskolin (1 microM) was found to stimulate progesterone production and VIP (0.1 to 1 microM) stimulated both the 3-HSD activity and the estradiol production. These data suggest that the absence of steroidogenic response to LH before day 4 postpartum could be explained by the absence of receptors, though the LH transmembrane signal-transduction system is functional in fetal ovaries.(ABSTRACT TRUNCATED AT 250 WORDS)     

Secretion of pregnane compounds from polycystic ovaries of androgen-sterilized rats

Progesterone, 5 alpha-pregnane-3,20-dione (5 alpha-DHP), 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha-OH), 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-DHP), 20 alpha-hydroxy-5 alpha-pregnan-3-one, and 5 alpha-pregnane-3 alpha, 20 alpha-diol in ovarian venous plasma of androgen-sterilized rats treated with 25 IU of human chorionic gonadotropin (hCG) were assayed by gas chromatography. The compounds listed were essentially undetectable in polycystic ovaries of the androgen-sterilized rats. However, after injection of hCG, levels of these steroids were high. Levels of progesterone and 5 alpha-pregnane compounds reached a peak within 1 or 2 days after hCG treatment and then fell slowly. The level of 20 alpha-DHP reached a peak on day 4 after hCG treatment and remained high thereafter. Injection of 2 micrograms of luteinizing hormone (LH) before sample collection increased the secretion of progesterone at all times tested except when it was already at a peak. The secretion of 5 alpha-DHP and 3 alpha-OH was also increased by LH after hCG treatment, but the ability of the ovary to produce these steroids was not, suggesting that there was low 5 alpha-reductase activity in the cystic ovary before hCG treatment. The results suggest that ovulation and luteinization in cystic follicles may cause the low activities of 5 alpha-reductase and 20 alpha-hydroxysteroid dehydrogenase in polycystic ovaries of androgen-sterilized rats to increase.     

Follicle-stimulating hormone plays a role in the induction of ovarian follicular cysts in hypophysectomized rats.

Unabated stimulation by low doses of LH-like activity produces ovarian follicular cysts in both progesterone-synchronized immature rats and pregnant rats. Serum FSH is maintained in both of these models at values similar to those observed on diestrus. To determine whether unabated stimulation by basal serum FSH affects the ability of LH-like activity to induce cystic ovaries, immature hypophysectomized (HYPOXD) rats were given either no hormone (control); 2 micrograms ovine FSH (oFSH) once daily for 14 days beginning on Day 27; 0.5 IU hCG twice daily for 13 days beginning on Day 28 of age; or both oFSH and hCG (FSH + hCG) beginning on Day 27 and Day 28, respectively. By the end of the in vivo treatments (Day 40 of age), the largest follicles in the ovaries of control and hCG-treated HYPOXD rats were at the preantral stage of development, whereas the largest follicles present in ovaries from FSH-treated animals were atretic and at the small antral stage of development. In contrast, ovaries from rats treated with FSH + hCG displayed large follicular cysts by Day 37 of age. Of the serum steroids analyzed, only estradiol and androstenedione concentrations for animals treated with FSH + hCG were consistently elevated above values observed for control HYPOXD rats. Serum testosterone and dihydrotestosterone values were similar for hCG-treated and control HYPOXD rats throughout the in vivo treatments. In contrast, these steroids were elevated between Days 3 and 5 of FSH treatment (+/- hCG treatment). Serum progesterone and estrone values for all in vivo gonadotropin treatment groups were similar to those of controls. Serum insulin concentrations were not affected by any in vivo treatment. Incubates of follicles/cysts from FSH + hCG-treated HYPOXD rats contained more progesterone, androstenedione, and estradiol than incubates of follicles from any other in vivo treatment group. Follicles from all in vivo treatment groups responded to 8-bromo cAMP (cAMP) with increased in vitro progesterone accumulation. However, only follicles from FSH-treated and FSH + hCG-treated rats responded to cAMP with increased androstenedione and estradiol accumulation in vitro. Inclusion of 400 ng of either androstenedione or testosterone in the incubation medium enhanced progesterone accumulation in follicular incubates from control, hCG-treated, and FSH-treated HYPOXD rats, but did not enhance progesterone accumulation in follicular incubates from FSH + hCG-treated animals. Both androstenedione and estradiol production increased markedly under these conditions for follicles from all in vivo treatment groups.(ABSTRACT TRUNCATED AT 400 WORDS)     

Binding of human chorionic gonadotropin by rat ovarian slices: dependence on the functional state of the ovary (38571).

Ovarian receptors specific for hCG-LH can be induced by PMSG-ovine LH priming. The marked increase in binding activity was accompanied by a rise in ovarian progesterone concentration and preceded by ovarian weight increase. The high binding activity of heavily luteinized ovaries was followed by a decline to prepriming levels during luteolysis. The ovarian progesterone content was decreased simultaneously and no change in ovarian weight was evident. The data demonstrate that ovarian hCG binding activity undergoes variation which depends on the functional state of ovaries.     

Ovarian FAM110C (family with sequence similarity 110C): induction during the periovulatory period and regulation of granulosa cell cycle kinetics in rats

FAM110C belongs to a family of proteins that regulates cell proliferation. In the present study, the spatiotemporal expression pattern of FAM110C and its potential role were examined during the periovulatory period. Immature female rats were injected with equine chorionic gonadotropin (eCG) followed by human chorionic gonadotropin (hCG) and ovaries or granulosa cells were collected at various times after hCG administration (n = 3/time point). Expression levels of Fam110c mRNA and protein were highly induced both in intact ovaries and granulosa cells at 8 to 12 h after hCG treatment. In situ hybridization analysis demonstrated Fam110c mRNA expression was induced in theca and granulosa cells at 4 h after hCG, primarily localized to granulosa cells at 8 h and 12 h, and decreased at 24 h after hCG. There was negligible Fam110c mRNA detected in newly forming corpora lutea. In rat granulosa cell cultures, hCG induced expression of Fam110c mRNA was inhibited by RU486, whereas NS398 and AG1478 had no effect, suggesting that Fam110c expression is regulated in part by the progesterone receptor pathway. Promoter activity analysis revealed that an Sp1 site was important for the induction of Fam110c expression by hCG. Overexpression of FAM110C promoted granulosa cells to arrest at the G(1) phase of the cell cycle but did not change progesterone levels. In summary, hCG induces Fam110c mRNA expression in granulosa cells by activation of an Sp1-binding site and the actions of progesterone. Our findings suggest that FAM110C may control granulosa cell differentiation into luteal cells by arresting cell cycle progression.     

In-vitro and in-vivo responsiveness of the corpus luteum of the mare to gonadotrophin stimulation

Dispersed horse luteal cells were used to evaluate the ability of horse LH, hCG and PMSG to stimulate progesterone secretion in vitro. Morphological characterization of these cells before gonadotrophin stimulation indicated the presence of two populations of cells based on cell diameters. In luteal cells incubated as suspended cells, horse LH and hCG stimulated (P less than or equal to 0.05) progesterone production at all levels of treatment. Stimulation of progesterone secretion by hCG was greater (P less than or equal to 0.05) than by horse LH over the range of concentrations utilized. When mares (N = 7) received an intramuscular injection of 1000 i.u. hCG on Days 3, 4 and 5 after the end of oestrus, there was an increase (P less than or equal to 0.05), in peripheral progesterone concentrations beginning on Day 7 and continuing until Day 14 compared with controls (N = 7). Peripheral progesterone concentrations continued to be elevated in hCG-treated mares for Days 15-30 after oestrus in those mares that conceived. Although treatment with hCG increased progesterone concentrations, it had no influence on anterior pituitary release of LH as measured by frequency and amplitude of LH discharge. We conclude that the mare corpus luteum is responsive to gonadotrophins in vitro and that exogenous hCG can enhance serum progesterone concentrations throughout the oestrous cycle and early pregnancy.     

Pregnenolone sulphate-independent inhibition of TRPM3 channels by progesterone

Transient Receptor Potential Melastatin 3 (TRPM3) is a widely expressed calcium-permeable non-selective cation channel that is stimulated by high concentrations of nifedipine or by physiological steroids that include pregnenolone sulphate. Here we sought to identify steroids that inhibit TRPM3. Channel activity was studied using calcium-measurement and patch-clamp techniques. Progesterone (0.01-10μM) suppressed TRPM3 activity evoked by pregnenolone sulphate. Progesterone metabolites and 17β-oestradiol were also inhibitory but the effects were relatively small. Dihydrotestosterone was an inhibitor at concentrations higher than 1μM. Corticosteroids lacked effect. Overlay assays indicated that pregnenolone sulphate, progesterone and dihydrotestosterone bound to TRPM3. In contrast to dihydrotestosterone, progesterone inhibited nifedipine-evoked TRPM3 activity or activity in the absence of an exogenous activator, suggesting a pregnenolone sulphate-independent mechanism of action. Dihydrotestosterone, like a non-steroid look-alike compound, acted as a competitive antagonist at the pregnenolone sulphate binding site. Progesterone inhibited endogenous TRPM3 in vascular smooth muscle cells. Relevance of TRPM3 or the progesterone effect to ovarian cells, which have been suggested to express TRPM3, was not identified. The data further define a chemical framework for competition with pregnenolone sulphate at TRPM3 and expand knowledge of steroid interactions with TRPM3, suggesting direct steroid binding and pregnenolone sulphate-independent inhibition by progesterone.     

Effect of 80 kDa protein of porcine follicular fluid on gonadotropin stimulated progesterone production in rat granulosa cells in vitro.

We reported the presence of a 80 kDa polypeptide in porcine follicular fluid that inhibited the binding of 125I-radiolabelled hFSH as well as hCG to the rat ovarian gonadotropin receptors. In the present study, the biological activity of the receptor binding inhibitor is determined using an in vitro bioassay procedure. Granulosa cells isolated from PMSG primed immature rat ovaries respond to exogenously added gonadotropins in terms of progesterone production. Addition of fractions containing the gonadotropin receptor binding inhibitory activity inhibited progesterone production stimulated by the gonadotropins in a dose-dependent fashion. The receptor binding inhibitory activity was also capable of inhibiting progesterone production stimulated by PMSG, which has both FSH- and LH-like activities in rats. In contrast, progesterone production stimulated by dbcAMP was not inhibited by the receptor binding inhibitor. This result indicates that the site of action of the inhibitor is proximal to the formation of the cAMP. The above observations point out to a possible role for this factor in modulating gonadotropin activity at the ovarian level.     

Effect of genetically defined oocyte depletion on production of androgens and oestrogens by ovaries of suckling mice

Steroid production and histological features of ovaries were compared either among normal +/+ mice of 3-12 days of age or among 12-day old mutant mice with various degrees of oocyte depletion. Whole ovaries were cultured in the medium containing [3H]progesterone and hCG or 4-androstene-3,17-dione and FSH; amounts of [3H]androgens or oestrogens released from the ovaries were assayed. FSH-responsive aromatase activity was detectable in ovaries of +/+ mice on day 3 after birth (2.6 +/- 0.4 pmol/2 ovaries/48 h), but the activity producing androgens from progesterone, under stimulation of hCG, was not detectable even on day 6 after birth (less than 0.1 pmol/2 ovaries/48 h). The androgen-producing activity appeared on day 9 after birth (1.16 +/- 0.25 pmol/2 ovaries/48 h), when follicles with more than two layers of granulosa cells developed. The ovaries of 12-day old Sl/Slt mice contained a considerable number of follicles with a single layer of granulosa cells, but did not contain any follicles with more than two layers of granulosa cells. The ovaries of Sl/Slt mice possessed aromatase activity (3.3 +/- 0.4 pmol/2 ovaries/48 h) but, not androgen-producing activity (less than 0.1 pmol/2 ovaries/48 h). The present results suggest that development of follicles with more than two layers of granulosa cells may induce the activity producing androgens from progesterone under stimulation of LH in suckling mouse ovaries, though the FSH-responsive aromatase activity is present even in follicles with a single layer of granulosa cells.     

Relationship between luteinizing hormone and decidual luteotropin in the maintenance of luteal steroidogenesis

Between Days 6-11 of pregnancy or pseudopregnancy, the decidual tissue of the rat produces a prolactin-like hormone, decidual luteotropin, which can sustain luteal progesterone production when prolactin is suppressed. However, this effect is dependent upon the presence of the pituitary. The present investigation was undertaken to determine whether decidual luteotropin and luteinizing hormone (LH) act together to sustain luteal steroidogenesis and if so, to find out whether the need for LH is due to the inability of the decidual tissue to produce LH-like material and/or whether LH affects decidual luteotropin production. Pseudopregnant rats with or without decidual tissue were hypophysectomized on Day 8 and treated with either 1.5 IU human chorionic gonadotropin (hCG)/day or with vehicle. Within 24 h, serum progesterone dropped in both vehicle-treated groups and decidual luteotropin levels declined by 80% in the decidual tissue. Human CG administration had no effect on progesterone production in the control group. Yet in rats with decidual tissue, hCG stimulated progesterone production for at least 48 h and maintained the decidual tissue content of decidual luteotropin. Progesterone, but not hCG treatment, maintained decidual luteotropin concentrations in ovariectomized rats. To compare the luteotropic activity of the decidual tissue with that of the placenta, pregnant or pseudopregnant rats with decidual tissue were hypophysectomized on Day 8 and treated with 1.5 IU hCG. Control groups had decidual tissue or placentas removed and were similarly treated. Human CG stimulated progesterone production only in rats with placental or decidual tissue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tachykinins in the normal and gonadotropin-stimulated ovary of the mouse

In this investigation, substance P (SP) and neurokinin A (NKA) concentrations have been determined in the ovary of control prepubertal mice, and prepubertal mice injected with pregnant mare serum (PMS) gonadotropin, an equine gonadotropin with predominant FSH action, or with PMS followed by human chorionic gonadotropin (hCG), which produces heavily luteinized ovaries after the stimulation with PMS. Control animals were injected with saline. The ovaries of animals treated with gonadotropins were heavier than the control ovaries, the combination of PMS plus hCG produced significantly heavier ovaries than PMS alone. The concentrations of SP and NKA in the ovaries of the animals treated with PMS or PMS/hCG were significantly lower than in control ovaries. No significant differences in ovarian tachykinin concentrations were observed between PMS and PMS/hCG-treated animals. The total ovarian content of SP was lower in PMS-injected animals as compared with the controls. The total ovarian content of NKA was not significantly different in the three groups of animals studied. These results show that ovaries stimulated with gonadotropins have lower concentrations of tachykinins than normal ovaries at the same age. It is therefore evident that gonadotropins can affect tachykinin stores in the ovaries of mice.     

Ovarian steroid synthesis in tissue culture after administration of hormones and epidermal growth factor

The features of steroidogenesis of immature mouse ovaries in culture under the influence of follicle-stimulating hormones (FSH), human chorionic gonadotropin (hCG), epidermal growth factor (EGF) and insulin have been investigated during the period of reinitiation of meiosis in the oocytes. Secretion of progesterone is stimulated after addition of FSH, hCG and of insulin and EGF combination to the medium. EGF increases FSH-stimulated progesterone secretion and inhibits estradiol secretion. The ratios progesterone/estradiol and testosterone/estradiol increase, when EGF is added to the culture medium. It is analogous to the action of hCG. It is suggested that EGF may be an intrafollicular EGF regulator of luteinizing hormone action on the sex and somatic cells of the mammalian ovaries.     

Relationship between in vivo and in vitro 17 alpha-hydroxylase and C17,20-lyase activity in ovaries of immature hypophysectomized rats treated chronically with human chorionic gonadotropin

The production of 3H2O from 17 alpha-3H-progesterone and 14CH3COOH from [21-14C]progesterone were used to measure the 17 alpha-hydroxylase and C17,20-lyase activities respectively in the microsomal + mitochondrial fraction of homogenates of ovaries from immature hypophysectomized rats chronically treated with human chorionic gonadotropin (hCG). The highly stimulated thecal and interstitial tissues were considered the only source of enzyme. hCG produced an increase in 17-hydroxyprogesterone, and androstenedione, but a drastic decrease in enzyme activity within 6 h; this could be largely prevented by pretreatment of the rats with cycloheximide or aminoglutethimide but actinomycin D was ineffective. After a nadir at 24 h, enzyme activities increased to more than double those of the starting level; this could be prevented by cycloheximide. Maximal activity levels were greatly decreased by cycloheximide and modestly increased by aminoglutethimide. Cessation of treatment at 60 h followed by a single injection of hCG 24 h later did not cause a loss, but delays of 36 or more hours produced a dramatic decrease in enzyme activity, which could be prevented by aminoglutethimide. The results indicate that the level of activity of these enzymes attained in the ovary following exposure to hCG is determined by a balance between the amount of substrate provided and production of enzyme and/or stimulating factors. Therefore, maintenance of increased enzyme activity induced by gonadotropin appears to be under genomic control.     

Circulating hormone concentrations in hypothyroid rats with induced polycystic ovaries

The induction of polycystic ovaries in hypothyroid rats by human chorionic gonadotropin (hCG) has been studied for many years. A complete understanding of this phenomenon requires information regarding the circulating levels of the hormones of the hypophyseal-gonadal axis. In this study, serum prolactin (PRL), luteinizing hormone (LH), estradiol, testosterone, and progesterone were measured by radioimmunoassay at intervals during the 40-day period in which large ovarian cysts were induced in hypothyroid rats by daily injections of hCG. After 20 injections, ovaries increased in weight 10-fold, and well-developed ovarian cysts were present, accompanied by lutein tissue; cyst development continued for the subsequent 20 days of hCG. Both PRL and LH rose during the first 5 days of treatment and were maintained at high levels from day 20 on. The pattern of change of gonadal steroids showed greater increases with hCG in hypothyroid than in euthyroid rats. Levels of estradiol in hypothyroid, hCG-injected rats increased in parallel to ovarian hypertrophy, whereas progesterone was high in initial stages and then declined. Testosterone increased in both euthyroid and hypothyroid animals, with no clear pattern coincident with cyst formation. The data suggest that the formation of polycystic ovaries in the hypothyroid rat is associated with high levels of PRL and LH followed by elevations of estradiol, which may serve to maintain continuous PRL, as well as LH, stimulation of the ovary.     

Modulation of 17 alpha-hydroxylase/C17,20-lyase activity in porcine theca cells

The major source of ovarian androgen is the theca cells. Androgens are produced by the conversion of progestins by the 17 alpha-hydroxylase/C17,20 lyase enzymatic system (lyase). The 3 beta-hydroxysteroid dehydrogenase and aromatase enzymes in the theca cells are modulated by gonadotropins as well as by steroids produced locally. Therefore, the combined effects of hCG plus progesterone, estradiol, or dihydrotestosterone (DHT) on microsomal lyase activity in theca cells from large and medium-sized follicles were determined. Theca cells (3 x 10(6) cells/6 ml/well) were cultured in Medium 199 (M199) containing only insulin (10 micrograms/ml) and transferrin (5 micrograms/ml). At 24 h, theca cells were treated with M199, hCG (15 ng/ml), progesterone, estradiol, or DHT (100 ng/ml) or a combination of hCG + one of the three steroids. Media were removed at various times of culture (27-72 h) and levels of androgen determined by RIA. Microsomes were incubated with 1 microCi [3H]progesterone +0.5 mM NADPH and radioactive conversion products were measured after purification by thin layer chromatography. Administration of progesterone, estradiol, or DHT alone had little effect on lyase activity in theca cells from medium-sized follicles whereas the addition of hCG alone significantly increased lyase activity in these cells. However, concomitant addition of any steroid with hCG inhibited the increase in lyase activity after the addition of hCG alone. Theca cells from large porcine follicles had a higher basal level of lyase activity compared to theca cells from the smaller follicles. Lyase activity in theca cells from large follicles was enhanced by progesterone; estradiol was inhibitory. DHT initially stimulated lyase activity in theca cells from large follicles, but was inhibitory later in culture. In contrast to its marked effect on theca cells from medium follicles, hCG had only a small effect on lyase activity in theca cells from large follicles. Thus, thecal lyase activity increased as the follicle matured, providing more androgen substrate for the production of estrogen. Lyase activity in theca cells of medium follicles appears to be regulated predominantly by gonadotropin from the pituitary while intraovarian regulation of lyase activity by steroids may be more important in larger follicles.     

孕马血清促性腺激素和氯地酚对猕猴超数排卵效果的观察

用孕马血清促性腺激素,总剂量为1550—2000单位,分4—7天处理猕猴,可促使其每侧卵巢出现滤泡超数发育,随后静脉注射入绒毛膜促性腺激素2500单位,在24小时内,猕猴即可出现超数排卵。     

Effects of rhFSH regimen and time interval on ovarian responses to repeated stimulation cycles in rhesus monkeys during a physiologic breeding season

We studied the effects of repeated stimulation by recombinant human FSH (rhFSH) at various time intervals during a physiologic breeding season in rhesus monkeys. Ovarian recovery and responses were assessed by ultrasonography, serum steroid concentrations, number of oocytes retrieved, and in vitro blastocyst development following IVF. One group underwent a single stimulation regimen with 18 IU rhFSH i.m., followed by 1000 IU hCG, and serum steroid concentrations and ovarian status were determined in the following three menses. Another group was stimulated as before and then allocated into three subgroups; each subgroup was re-stimulated once at the beginning of the ensuing first, second, or third menses. In the final experiment, one group was stimulated with 37.5 IU rhFSH, whereas another group received 18 IU rhFSH. In subsequent cycles, all were re-stimulated twice with 18 IU rhFSH at time intervals of two menstrual cycles (MCs). At the first menses after stimulation, serum progesterone concentrations were significantly higher and the ovaries larger than before stimulation. Monkeys that were re-stimulated at the first menses responded poorly; at the second menses, progesterone concentrations and ovarian size recovered, but the number of oocytes retrieved from re-stimulated monkeys was still significantly reduced. However, animals that were re-stimulated in two MCs later responded well (i.e., percentage of the animals responding, oocytes recovered, and potential for fertilization and blastocyst formation). In conclusion, rhesus monkeys were likely to have similar ovarian responses to repeated stimulation with the same regimen spaced at least two MCs apart.     

Premature luteal regression in goats superovulated with PMSG: effect of hCG or GnRH administration during the early luteal phase

Twenty-two goats were superovulated with PMSG; 84 h after the onset of estrus the goats were treated with saline solution (control group n = 7), hCG (hCG group, n = 7), or GnRH (GnRH group, n = 8). The ovaries of all the goats were laparoscopically examined 3 and 6 d after the onset of estrus. In each case the CL were counted and classified according to their appearance as normal-looking or as regressing. Blood samples for progesterone determination were collected every 12 h from Day 1 to Day 6. Premature luteal regression was considered to have occurred if progesterone concentrations declined to less than 1 ng/mL by Day 6. According to progesterone concentrations, 57.5, 0 and 37.5% of the goats underwent premature luteal regression in the control, hCG and GnRH groups, respectively. Progesterone concentrations were higher in the hCG group than in the other groups on Days 5 and 6 post estrus (P < 0.05). The control group was the only one in which there was a significant (P < 0.05) increase in the number of regressing CL between Day 3 (1.6 +/- 1.4) and Day 6 (7.3 +/- 1.4). It was also the only group in which there was a significant decrease in the number of normal-looking CL between Day 3 (12.6 +/- 2.1) and Day 6 (2.6 +/- 2.1). On Day 6 the animals treated with hCG had significantly more normal-looking CL (12.0 +/- 2.3) than those in the control group (2.6 +/- 2.1). The number of large follicles present on the ovaries on Day 6 post estrus had negative correlations with progesterone concentrations (P = 0.05) and with the number of normal-looking CL (P < 0.05). It is concluded that the administration of hCG 84 h after the onset of estrus prevents premature luteal regression in goats superovulated with PMSG.     

Effects of testosterone, estradiol, aromatase inhibitor, gonadotropin and prolactin on the response of mouse testes to acute gonadotropin stimulation

These studies determined the local acute responsiveness of the testis to intratesticular administration of human chorionic gonadotropin (hCG) under basal, stimulated (systemic hCG pre-treated), hypogonadotropic (steroid pre-treatment) and hyperprolactinemic conditions in male mice. In addition, testicular testosterone (T) levels were determined after intratesticular administration of the aromatase inhibitor, 4-hydroxyandrostenedione (4-OHA) or progesterone under basal or hCG-stimulated conditions. Intratesticular administration of 0.025, 0.25, 2.5 or 25 mIU hCG resulted in a dose-dependent (3- to 14-fold) increase in testicular T concentrations in hCG compared to vehicle-injected testes. Systemic (i.p.) pre-treatment with 5 IU hCG 24 h before prevented any further increases in the already elevated (10-fold basal) T levels after direct intratesticular hCG injection. Pretreatment with 250 micrograms testosterone propionate (TP) reduced basal testicular T concentrations, but resulted in increased responsiveness to intratesticular hCG administration. In contrast, estradiol benzoate (EB) pretreatment, which also reduced basal testicular T concentrations, did not affect the testicular responsiveness to hCG. Hyperprolactinemia reduced testicular responsiveness to intratesticular administration of 0.025, 0.25 or 2.5 mIU hCG, but basal levels of testicular T were elevated. One hour after intratesticular injections of an aromatase inhibitor, 4-OHA; (0.25 micrograms) testis, T levels were increased in males pre-treated with 5 IU hCG (i.p.) 24 h earlier. Higher doses of 4-OHA (2.5, 25 or 250 micrograms) resulted in significant, dose-related increases in basal testicular T levels which were attenuated by hCG-pre-treatment. Intratesticular administration of 20 micrograms progesterone increased testicular T concentrations 2.7-fold, but this effect was attenuated (1.5-fold) in hCG-pre-treated mice, suggesting that enzymatic lesions beyond progesterone may be involved in hCG-induced testicular desensitization. These results indicate that testicular responsiveness to hCG depends on the existing levels of gonadotropic stimulation. However, it is evident that estrogens and prolactin also influence the sensitivity of the testis to gonadotropin.