Progesterone is a mediator in the ovulatory process of the in vitro-perfused rat ovary

The role of steroids in the ovulatory process of the rat was explored in an in vitro perfusion system. Immature rat ovaries were primed with pregnant mare's serum gonadotropin (20 IU) and perfused in a recirculating perfusion system for up to 20 h. Unstimulated ovaries did not ovulate whereas the addition of luteinizing hormone (LH; 0.1 micrograms/ml) plus 3-isobutyl-1-methylxanthine (IBMX; 0.2 mM) resulted in 13.6 +/- 1.0 ovulations per treated ovary. Addition of an inhibitor of 3 beta-hydroxysteroid dehydrogenase (Compound A; 10 micrograms/ml) significantly (p less than 0.01) decreased the number of ovulations after LH plus IBMX stimulation (1.6 +/- 0.8 ovulations per treated ovary). This inhibition was reversed by the addition of progesterone, with 6.6 +/- 2.1 ovulations at approximately 100 ng/ml progesterone in the perfusion medium and 15.2 +/- 3.4 ovulations at approximately 3000 ng/ml progesterone. The addition of testosterone (10 micrograms/ml) did not reverse the inhibition of ovulations by Compound A. High levels of progesterone in the perfusion medium (greater than 3000 ng/ml) did not significantly (p greater than 0.05) increase the number of ovulations after stimulation with LH plus IBMX (20.2 +/- 4.8 ovulations), and progesterone (greater than 3000 ng/ml) was not by itself able to induce ovulations. Addition of LH plus IBMX resulted in a marked increase in the levels of progesterone, testosterone, and estradiol in the perfusion medium. The production of these steroids was almost completely inhibited by the addition of Compound A, and the levels of testosterone and estradiol were restored by the addition of high concentrations of progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Development of steroidogenic activity in the ovary of the prepubertal hamster: II. Production of steroids from steroidal precursors and response in vitro to cyclic adenosine monophosphate and luteinizing hormone

In vitro exposure for 2 h to 250 ng/ml of pregnenolone led to increased production of progesterone and 17 alpha-hydroxyprogesterone (17 alpha-OHP) by hamster ovaries on Days 5, 10 and 15 of age. Similar incubations with 250 ng/ml progesterone or androstenedione caused significant increases in 17 alpha-OHP or testosterone, respectively. When testosterone was added in doses of 32.5, 250 and 500 ng/ml to ovaries on Days 5-30, as early as Day 5 the ovaries aromatized the androgen to estradiol. Day 30 ovaries were the most efficient in the conversion because antral follicles, the principal site for aromatization, were then present. In terms of progesterone production, 400 ng/ml of luteinizing hormone (LH) during 4 h of in vitro incubation stimulated ovaries on Days 5, 10 and 15. Cyclic adenosine 3':5' monophosphate (cAMP) at a dose of 1 mM and 5 mM stimulated progesterone production by Days 5 and 10 ovaries more efficiently than LH. However, Day 15 ovaries produced more progesterone in response to LH compared to cAMP. These experiments establish that the steroidogenic enzymes differentiate at a very early age in the hamster ovary, even before the appearance of gonadotropin receptors. The inability of the early postnatal ovary to produce steroids is apparently attributable to lack of precursors such as cholesterol or cholesterol side chain cleavage enzymes.     

Regulation of prostaglandin endoperoxide synthase by cyclic adenosine 3',5'-monophosphate in the in vitro-perfused rat ovary

The preovulatory regulation of two enzymes in the prostaglandin biosynthetic pathway, prostaglandin endoperoxide synthase (PGS) and prostacyclin synthase (ISN), was examined in granulosa cells and residual tissue of rat ovaries perfused in vitro. Ovaries from rats primed with pregnant mare's serum gonadotropin (20 IU) were perfused for up to 20 h starting the morning of induced proestrus. The amounts of PGS and ISN present were analyzed with immunoblotting techniques. Soluble extracts from granulosa cells and residual ovarian tissues were obtained at different times (0 h, 3 h, 7 h, 12 h) after treatment in vitro with luteinizing hormone (LH, 0.1 microgram/ml) and 3-isobutyl-1-methylxanthine (IBMX; 0.2 mM) and at 7 h in untreated control ovaries or after treatment with forskolin (30 microM) or LH (0.1 microgram/ml). The levels in the perfusion medium of cyclic adenosine 3',5'-monophosphate (cAMP), progesterone, testosterone, and estradiol were measured and the number of ovulations were examined. The levels of PGS after treatment with LH + IBMX increased up to 7 h and remained high at 12 h, a time that is close to the time of ovulation. The increase was more pronounced in the granulosa cells than in the residual tissue. Treatment with forskolin induced synthesis of PGS in granulosa cells, and the levels at 7 h were similar to those after stimulation with LH + IBMX. The levels of PGS were lower in granulosa cells of the group stimulated with LH alone than in granulosa cells from ovaries stimulated with LH + IBMX or forskolin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation of ovarian binding of 125I-HCG with formation of cAMP, estradiol and progesterone during pregnancy.

The content of ovarian gonadotropin receptors in rat was found to change during pregnancy. The specific binding of 125I-HCG to ovarian homogenates rose to its maximal values on days 13 and 16. Thereafter, the binding declined as parturition approached. No consistent changes in responsiveness of rat ovary to LH in synthesis of cAMP and estradiol were observed during pregnancy. Plasma estradiol concentration increased on day 16 and remained high throught days 21 and 22. Progesterone levels increase steadily during the first half of pregnancy and then fall, especially sharply on day 21 and 22. The results demonstrate that the secretion of progesterone correlates with gonadotropin receptors during pregnancy.     

Neonatal release of gonadotropins is essential for development of ovarian follicle-stimulating hormone receptors

In the rat, ovarian follicle-stimulating hormone (FSH) receptors increase markedly during the first two postnatal weeks, when serum gonadotropin levels are most elevated. This study was conducted to evaluate the hypothesis that these high gonadotropin levels, and in particular FSH, are involved in the acquisition of FSH receptors by the developing ovary. Gonadotropin release was suppressed by administration of several non-aromatizable androgens, among which dihydrotestosterone propionate (DHTP) was the most effective. In one series of experiments the steroids were administered from Days 5 to 11, and serum FSH and luteinizing hormone (LH) were measured on Day 12. Surprisingly, FSH receptor content was greater in rats with suppressed serum gonadotropins than in controls. The greatest increase in available receptors was observed in DHTP-treated rats in which serum FSH was reduced to 20% of control values and LH suppressed to undetectable values. DHTP failed to directly increase available FSH receptors in hypophysectomized immature rats. Magnesium chloride (MgCl2) treatment of ovarian membranes removed bound 125I-hFSH by 87% without affecting receptor viability. Exposure of control 12-day-old ovaries to MgCl2 increased available FSH receptors to a level similar to that of ovaries from DHTP-treated rats not exposed to MgCl2, suggesting that more receptors were available in DHTP-treated rats because serum FSH was suppressed. Earlier initation of DHTP treatment (postnatal Day 1) suppressed serum FSH and LH to undetectable values by Day 5 and decreased FSH receptor content below control values by Day 12. MgCl2 treatment only slightly increased available receptors in these DHTP-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

Examination of the role of follicle stimulating hormone in estrogen biosynthesis in vivo and in vitro in the ovary of the cyclic hamster

The effect of neutralizing endogenous follicle stimulating hormone (FSH) or luteinizing hormone (LH) with specific antisera on the in vivo and in vitro synthesis of estrogen in the ovary of cycling hamster was studied. Neutralization of FSH or LH on proestrus resulted in a reduction in the estradiol concentration of the ovary on diestrus-2 and next proestrus, suggesting an impairment in follicular development. Injection of FSH antiserum at 0900 h of diestrus-2 significantly reduced the ovarian estradiol concentration within 6--7 h. Further, these ovaries on incubation with testosterone (T) in vitro at 1600 h of the same day or the next day synthesized significantly lower amounts of estradiol, compared to corresponding control ovaries. Although testosterone itself, in the absence of endogenous FSH, could stimulate estrogen synthesis to some extent, FSH had to be supplemented with T to restore estrogen synthesis to the level seen in control ovaries incubated with T. Lack of FSH thus appeared to affect the aromatization step in the estrogen biosynthetic pathway in the ovary of hamster on diestrus-2. In contrast to this, FSH antiserum given on the morning of proestrus had no effect on the in vivo and in vitro synthesis of estrogen, when examined 6--7 h later. The results suggest that there could be a difference in the need for FSH at different times of the cycle. Neutralization of LH either on diestrus-2 or proestrus resulted in a drastic reduction in estradiol concentration of the ovary. This block was at the level of androgen synthesis, since supplementing testerone alone in vitro could stimulate estrogen synthesis to a more or less similar extent as in the ovaries of control hamsters.     

In vitro steroidogenesis by dissociated rat follicles, primary to antral, before and after injection of equine chorionic gonadotropin.

Prepubertal female rats were injected s.c. with 5.0 IU eCG, and ovaries were collected 24 and 48 h post-eCG, on Day 25, as well as from an untreated group also on Day 25. Large antral follicles were manually dissected, and the ovarian remnants were incubated with collagenase overnight to liberate preantral follicles from adhering stromal cells. The viability of the follicles was established by normal histology and lack of pyknotic granulosa cells (GCs) and by their ability to secrete steroids. After a 1-h baseline incubation, either 10 ng LH or 100 ng FSH was added for an additional hour, and the media-before and after gonadotropin administration-were used to measure progesterone, androstenedione, and estradiol by RIA. A distinct hierarchy existed in steroid synthesis, with the maximal production by the largest (700 microm) antral follicles. The major steroid that had accumulated after addition of LH at 48 h post-eCG was androstenedione (1099 pg/follicle per hour), followed by equal amounts of progesterone (155 pg/follicle per hour) and estradiol (191 pg/follicle per hour). There was a precipitous drop in steroid production by 550-microm and 400-microm antral follicles, especially in estradiol for the latter-sized follicles (0.08 pg/follicle per hour). Preantral follicles also produced progesterone and androstenedione after addition of LH. For example, follicles 222 microm in diameter with 4-5 layers of GCs and well-developed theca responded to LH at 48 h post-eCG by accumulating androstenedione (37 pg/follicle per hour) and progesterone (6 pg/follicle per hour) but negligible estradiol. The smallest follicles secreting steroids, 110-148 microm in diameter, had 2-4 layers of GCs. However, primary follicles (1 layer of GCs and no theca) did not synthesize appreciable amounts of any steroid. Although small preantral follicles were consistently stimulated by LH, FSH was ineffective. This result differs from findings in the hamster showing that intact preantral follicles with 1-4 layers of GCs and no theca respond to FSH by secreting progesterone in vitro (Roy and Greenwald, Biol Reprod 1987; 31:39-46). The technique developed to collect intact rat follicles should be useful for numerous investigations.     

In vitro and in vivo studies with aromatase inhibitor 4-hydroxy-androstenedione

Studies with 4-hydroxyandrostenedione (4-OHA) are described which demonstrate inhibition of aromatase in human placentra and rat ovaries. In animal experiments, the compound was compared with aminoglutethimide (AG) for antitumor activity and effects on plasma hormone levels. 4-OHA was more effective than AG in causing regression of DMBA-induced hormone dependent tumors in the rat. Although estradiol concentrations in ovarian vein blood were reduced initially by both compounds, there is a reflex rise in LH and estradiol levels during long-term treatment with AG, whereas hormone levels in 4-OHA treated animals remained suppressed. Further studies in ovariectomized rats indicated that during long-term treatment, 4-OHA acts as a weak androgen (the compound has less than 1% the activity of testosterone) to directly inhibit the post-castrational rise in gonadotropin levels. This antigonadotropin action of the steroidal aromatase inhibitor may help maintain reduced ovarian estrogen secretion and thus contribute to the antitumor activity of 4-OHA.     

Modulatory actions of estradiol and progesterone on phorbol ester-stimulated LH secretion from cultured rat pituitary cells.

We compared the ability of estradiol and progesterone to modulate gonadotropin-releasing hormone (GnRH) and protein kinase C (PKC)-mediated luteinizing hormone (LH) secretion. Long-term (48 h) treatment of rat pituitary cells with 1 nM estradiol enhanced GnRH and phorbol ester (TPA)-stimulated LH secretion. This positive effect was facilitated by additional short-term (4 h) treatment with progesterone (100 nM). However, long-term progesterone treatment, which inhibited GnRH-stimulated LH secretion, did not influence TPA-stimulated gonadotropin release. These steroid actions occurred without an effect on the total amount of LH in the cell cultures (total LH = LH secreted + LH remaining in the cell) and neither the secretagogues nor the steroids altered total LH. Since GnRH or TPA-induced LH secretion depends on Ca2+ influx into the gonadotroph, we also analyzed the effects of estradiol and progesterone under physiological extracellular Ca2+ concentrations and in the absence of extracellular Ca2+. The steroids were able to influence GnRH or TPA-induced LH secretion under both conditions. However, when TPA was used as stimulus in Ca(2+)-deficient medium the relative changes induced by estradiol and progesterone were more pronounced, possibly indicating that the extracellular Ca(2+)-independent component of PKC-mediated LH secretion is more important for the regulation of the steroid effects. It is concluded that estradiol and progesterone might mediate their modulatory actions on GnRH-stimulated LH secretion via an influence on PKC. This effect can occur independently from de novo synthesis of LH and Ca2+ influx into gonadotrophs.     

Improved model for the induction of proestrus-like gonadotropin surges in long-term ovariectomized rats

In long-term (greater than 4 wk) ovariectomized rats the positive response of the gonadotropin release apparatus to a priming dose of estradiol is moderate as compared with that of proestrous rats exposed to endogenous estradiol. In the present study, high sensitivity to estrogen was restored in long-term ovariectomized rats by pretreatment with estradiol benzoate (EB, 20 micrograms, day 0) and progesterone (P, 2.5 mg, day 3). Estradiol benzoate (20 micrograms) given on day 5 induced proestrus-like surges of LH and FSH in the afternoon on day 6. Additional administration of P (2.5 mg at noon on day 6) had a facilitatory effect. Stimulation of LH release could be evoked in rats by the described regimen 1, 6 or 50 wk after ovariectomy. The long-term ovariectomized rat injected with EB and P as described might provide a useful model for neuroendocrinological investigations on the gonadotropin surge mechanism.     

In vivo β-adrenergic blockade by propranolol prevents isoproterenol-induced polycystic ovary in adult rats

Increasing evidence in animal models and in humans shows that sympathetic nerve activity controls ovarian androgen biosynthesis and follicular development. Thus, sympathetic nerve activity participates in the follicular development and the hyperandrogenism characteristics of polycystic ovary syndrome, which is the most prevalent ovarian pathology in women during their reproductive years. In this study, we mimic sympathetic nerve activity in the rat via "in vivo" stimulation with isoproterenol (ISO), a β-adrenergic receptor agonist, and test for the development of the polycystic ovary condition. We also determine whether this effect can be reversed by the administration of propranolol (PROP), a β-adrenergic receptor antagonist. Rats were treated for 10 days with 125 μg/kg ISO or with ISO plus 5 mg/kg PROP. The ovaries were examined 1 day or 30 days following drug treatment. While ISO was present, the ovaries had an increased capacity to secrete androgens; ISO + PROP reversed this effect on androgen secretory activity. 30 days after treatment, androstenedione secretion reverted to normal levels, but an increase in the intra-ovarian nerve growth factor (NGF) concentration and luteinizing hormone (LH) plasma levels was detected. ISO treatment resulted in follicular development characterized by an increased number of pre-cystic and cystic ovarian follicles; this was reversed in the ISO + PROP group. The lack of change in the plasma levels of progesterone, androstenedione, testosterone, or estradiol and the increased LH plasma levels strongly suggests a local intra-ovarian effect of ISO indicating that β-adrenergic stimulation is a definitive component in the rat polycystic ovary condition.     

Interaction between ovarian and adrenal steroids in the regulation of gonadotropin secretion

Recent work from our laboratory suggests that a complex interaction exists between ovarian and adrenal steroids in the regulation of preovulatory gonadotropin secretion. Ovarian estradiol serves to set the neutral trigger for the preovulatory gonadotropin surge, while progesterone from both the adrenal and the ovary serves to (1) initiate, (2) synchronize, (3) potentiate and (4) limit the preovulatory LH surge to a single day. Administration of RU486 or the progesterone synthesis inhibitor, trilostane, on proestrous morning attenuated the preovulatory LH surge. Adrenal progesterone appears to play a role in potentiating the LH surge since RU486 still effectively decreased the LH surge even in animals ovariectomized at 0800 h on proestrus. The administration of ACTH to estrogen-primed ovariectomized (ovx) immature rats caused a LH and FSH surge 6 h later, demonstrating that upon proper stimulation, the adrenal can induce gonadotropin surges. The effect was specific for ACTH, required estrogen priming, and was blocked by adrenalectomy or RU486, but not by ovariectomy. Certain corticosteroids, most notably deoxycorticosterone and triamcinolone acetonide, were found to possess "progestin-like" activity in the induction of LH and FSH surges in estrogen-primed ovx rats. In contrast, corticosterone and dexamethasone caused a preferential release of FSH, but not LH. Progesterone-induced surges of LH and FSH appear to require an intact N-methyl-D-aspartate (NMDA) neurotransmission line, since administration of the NMDA receptor antagonist, MK801, blocked the ability of progesterone to induce LH and FSH surges. Similarly, NMDA neurotransmission appears to be a critical component in the expression of the preovulatory gonadotropin surge since administration of MK801 during the critical period significantly diminished the LH and PRL surge in the cycling adult rat. FSH levels were lowered by MK801 treatment, but the effect was not statistically significant. The progesterone-induced gonadotropin surge appears to also involve mediation through NPY and catecholamine systems. Immediately preceding the onset of the LH and FSH surge in progesterone-treated estrogen-primed ovx. rats, there was a significant elevation of MBH and POA GnRH and NPY levels, which was followed by a significant fall at the onset of the LH surge. The effect of progesterone on inducing LH and FSH surges also appears to involve alpha 1 and alpha 2 adrenergic neuron activation since prazosin and yohimbine (alpha 1 and 2 blockers, respectively) but not propranolol (a beta-blocker) abolished the ability of progesterone to induce LH and FSH surges. Progesterone also caused a dose-dependent decrease in occupied nuclear estradiol receptors in the pituitary.(ABSTRACT TRUNCATED AT 400 WORDS)     

Role of Thy-1+ and Ia+ cells in ovarian function

Cryostat sections of anovulatory ovaries from persistent estrous rats following a single postnatal dose of testosterone and from persistent diestrous rats following long-term postnatal estradiol treatment were investigated. The indirect immunoperoxidase technique was used to localize ovarian Thy-1 and Ia glycoproteins, as well as several other cell surface markers, and the results were compared with those obtained in normal ovaries of cycling females. Folliculogenesis in persistent estrous rats proceeded up to cystic antral follicles and was associated with the occurrence of Thy-1+ stromal cells under follicular basal lamina. In contrast to normal ovaries, Thy-1+ material did not invade the basal layers of granulosa cells. There was also no association of Ia+ cells with follicular basal lamina, but Ia+ cells were usually found associated with some thecal vessels. In persistent diestrous rats folliculogenesis was significantly retarded in both advanced antrum formation and thecal development. Thy-1+ cells were usually present in theca. No Thy-1+ material was found among basal layers of granulosa cells and the depletion of thecal Ia+ cells was almost complete. We suggest that normal follicular development may be dependent on the correct effects of Thy-1+ and Ia+ cells in addition to appropriate gonadotropin and steroid stimulation. On the other hand, anovulatory syndromes following postnatal androgen or estrogen treatment might be induced by temporary direct ovarian effects disturbing the establishment of the normal relationship between follicular structures and the immune system.     

Validation of the mechanisms proposed for the stimulatory and inhibitory effects of progesterone on gonadotropin secretion in the estrogen-primed rat: a possible role for adrenal steroids.

The stimulatory and inhibitory effects of progesterone on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion were found to be dependent on the length of estrogen exposure in ovariectomized estrogen-primed rats. Progesterone suppressed LH and FSH secretion when administered 16 hours after a single injection of estradiol to ovariectomized rats. If the estradiol treatment was extended over 40 hours by two injections of estradiol 24 hours apart, progesterone administration led to a highly significant elevation of both serum LH and FSH levels 6 hours later. In addition to the direct stimulatory effect on LH and FSH release, progesterone, when injected 1 hour before, was able to antagonize the suppressive effect of a third injection of estradiol on LH and FSH release. In the immature ovariectomized estrogen-primed rat, 10 IU of ACTH brought about a release of progesterone and corticosterone 15 minutes later and LH and FSH 6 hours later. Progesterone, but not corticosterone, appeared to be responsible for the effect of ACTH on gonadotropin release. The synthetic corticosteroid triamcinolone acetonide brought about LH and FSH release in the afternoon, while cortisol, similar to corticosterone, was unable to do so. Nevertheless, triamcinolone acetonide and cortisol brought about increased secretion of FSH the following morning.     

Ovulation in the perfused ovary in vitro: further evidence that estrogen is not required

The effect of inhibition of estrogen synthesis on ovulation in rat ovaries perfused in vitro with medium without phenol red was examined. The addition of luteinizing hormone (LH, 0.1 microgram/mL) plus 3-isobutyl-1-methylxanthine (IBMX, 0.2 mM) to phenol red-free perfusion medium (M199 + 4% bovine serum albumin) induced ovulation. The number of ovulations was similar to that found in medium containing phenol red. There was a similar increase in estradiol (1, 3, 5 (10)-estratriene-3, 17 beta-diol) levels in the medium in both groups. The addition of 4-hydroxy-4-androstene-3, 17-dione (4-OH-A, 5 microM) to phenol red-free medium blocked the increase in estradiol levels induced by LH + IBMX, but did not prevent ovulation. There was no significant difference in the number of ovulations in the three groups. In conclusion, phenol red in the perfusion medium does not influence ovulation induced by LH + IBMX. Furthermore, an increase in estrogen is not required during the immediate preovulatory period for ovulation to occur.     

Ontogeny of the gonadal receptor for luteinizing hormone in the pig

Homogenates of porcine ovaries and testes collected between 70 d post coitum and 42 d post partum were incubated with radiolabelled human chorionic gonadotropin (hCG) to determine the presence and relative amounts of luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptors. Specific binding of (125)I-hCG to ovaries and testes occurred at all stages of fetal and postnatal development. Ovarian tissue possessed relatively low affinity, high capacity LH/hCG binding sites that were most numerous at Day 80 of gestation and decreased thereafter. In contrast, high affinity, low capacity LH/hCG binding sites were found in the testes. In males, the total number of LH/hCG binding sites remained stable until near term and then increased with age, but the number of sites per gram of testicular tissue did not change (P>0.05). In summary, differential binding of LH/hCG in gonadal tissue occurred in male and female piglets during pre- and post-natal periods, and this binding reflected the known differential pattern of development of the male and female gonad.     

Estrogen production by fetal rat gonads

Aromatase activity in fetal rat testes and ovaries was demonstrated by the conversion of tritiated testosterone or 19-hydroxyandrostenedione into estrone and estradiol, which were identified and quantified by double isotopic dilution and recrystallization to constant specific activity. Testes formed mostly estradiol, ovaries mostly estrone. Aromatase activity was stimulated by cAMP in both the testes and ovaries as early as 17 days of fetal life. Stimulation by FSH was noted at this same stage in the testis, but not before 3–4 days after birth in the ovary. LH was without effect on aromatase activity in both kinds of gonads. Basal estrogen secretion was non-existent or undetectable in both the testes and ovaries in fetal stages. In the presence of cAMP and as early as 17 days of fetal life, the testes released estradiol, as early as 14 days the ovaries released estrone. Estrogen secretion was stimulated by LH and FSH at fetal stages in the testis and at infantile stages in the ovary. Responsiveness to gonadotrophins closely followed the appearance of the receptors.