Effects of the antiandrogen hydroxyflutamide on progesterone secretion by preovulatory rat follicles in vivo and in vitro.

Serum and ovarian progesterone levels and in vitro production of progesterone by preovulatory follicles were measured on proestrus in pregnant mare's serum gonadotropin (PMSG) primed immature rats in which the luteinizing hormone (LH) surge and ovulation were blocked by administration of the antiandrogen hydroxyflutamide. Serum progesterone levels observed at 12:00 on proestrus were significantly elevated, twofold above those observed in vehicle-treated controls, by in vivo administration of 5 mg hydroxyflutamide 4 h earlier. In control rats, proestrous progesterone did not increase until 16:00, in parallel with rising LH levels of the LH surge. No LH surge occurred in the hydroxyflutamide-treated rats, ovulation was blocked, and serum progesterone declined throughout the afternoon of proestrus, from the elevated levels present at 12:00. Administration of human chorionic gonadotropin (hCG) at 11:00 advanced the elevation of serum progesterone by 2 h in vehicle-treated controls and prevented the decline in progesterone levels in hydroxyflutamide-treated rats. The patterns of change in ovarian tissue concentrations with time and treatment were essentially similar to those observed for serum progesterone. In in vitro experiments, progesterone secretion during 24 h culture of preovulatory follicles obtained on PMSG-induced proestrus was significantly increased, sixfold, by addition to the culture media of 370 microM but not of 37 microM hydroxyflutamide. Testosterone (50 nM) and hCG (20 mIU/mL) caused 26- and 14-fold increases, respectively, in progesterone secretion by cultured follicles. Hydroxyflutamide significantly reduced the stimulatory effect of testosterone but not of hCG on progesterone secretion in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ability of progesterone to reverse anti-androgen (hydroxyflutamide)-induced interference with the preovulatory LH surge and ovulation in PMSG-primed immature rats

In Exp. 1, PMSG was injected to 26-day-old prepubertal rats to induce ovulations. On Day 2 (2 days later, the equivalent of the day of pro-oestrus) they received at 08:00 h 5 mg hydroxyflutamide or vehicle and at 12:00 h 2 mg progesterone or testosterone or vehicle. Animals were killed at 18:00 h on Day 2 or at 09:00 h on Day 3. Progesterone but not testosterone restored the preovulatory LH surge and ovulation in hydroxyflutamide-treated rats. In Exp. 2, 2 mg progesterone or testosterone were injected between 10:30 and 11:00 h on Day 2, to advance the pro-oestrous LH surge and ovulation in PMSG-primed prepubertal rats. Injection of hydroxyflutamide abolished the ability of progesterone to advance the LH surge or ovulation. Testosterone did not induce the advancement of LH surge or ovulation. In Exp. 3, ovariectomized prepubertal rats implanted with oestradiol-17 beta showed significantly (P less than 0.01) elevated serum LH concentrations at 18:00 h over those observed at 10:00 h. Progesterone injection to these animals further elevated the serum LH concentrations at 18:00 h, in a dose-dependent manner, with maximal values resulting from 1 mg progesterone. Hydroxyflutamide treatment significantly (P less than 0.003) reduced the serum LH values in rats receiving 0-1 mg progesterone but 2 mg progesterone were able to overcome this inhibition. It is concluded that progesterone but not testosterone can reverse the effects of hydroxyflutamide on the preovulatory LH surge and ovulation. It appears that hydroxyflutamide may interfere with progesterone action in induction of the LH surge, suggesting a hitherto undescribed anti-progestagenic action of hydroxyflutamide.     

Antiovulatory effect of a single injection of pure antiestrogen ZK 191703 at early stage of rat estrus cycle

The effects of ZK 191703 (ZK), a pure antiestrogen, on ovulation, follicle development and peripheral hormone levels were investigated in rats with 4-day estrus cycle and gonadotropin-primed immature rats in comparison to tamoxifen (TAM)-treatment. In adult rats, a single s.c. injection of ZK (5 mg/kg) or TAM (5 mg/kg) at an early stage of the estrus cycle (diestrus 9:00) inhibited ovulation, and was associated with suppression of the surge of preovulatory LH, FSH and progesterone. In rats treated with ZK or TAM at a late stage of the estrus cycle (proestrus 9:00), no inhibitory effects on ovulation, the gonadotropin and progesterone surge were detected. ZK treatment at diestrus 9:00, in contrast to TAM, increased the baseline LH level. When immature rats were treated with antiestrogens in the earlier stage of follicular development, 6 and 30 h but not 48 h or later after injection of gonadotropin (PMSG), ovulation was attenuated, associated with a lowered progesterone level. Unruptured preovulatory follicles were found in most of the ovaries from anovulatory animals treated with ZK or TAM. Antiestrogens, ZK and TAM administered at an early phase of the estrus cycle delay the follicular development functionally and inhibit ovulation in rats and suppression of the preovulatory progesterone surge.     

A secondary surge of prolactin on the estrus afternoon

It has been described that throughout the estrous cycle of the rat, plasma prolactin (PRL) is basal except on proestrus afternoon when a preovulatory surge occurs. However, there have been controversies about PRL levels on the estrus day. Thus, the aim of this study was to evaluate the existence of a secondary surge of PRL on estrus afternoon and correlate it with plasma estradiol levels. The jugular vein of cycling rats was cannulated at 14:00 h on proestrus and a blood sample was withdrawn at 17:00 h for plasma LH measurement and determination of the preovulatory LH surge occurrence. In order to exclude the regular cycling rats that do not present the gonadotropins preovulatory surge and do not ovulate, only rats showing the LH surge on proestrus were considered in this study. Blood samples were collected hourly during estrus from midnight to 9:00 h (group 1) and from 10:00 to 18:00 h (group 2). In group 1, PRL showed a descending profile from midnight to 9:00 h, whereas the estradiol concentrations were constant. In group 2, a secondary surge of PRL was observed in 20 of 25 (80%) rats and plasma estradiol remained constant, but was higher in animals with the PRL surge. Thus the present data suggest the occurrence of a secondary surge of PRL in the afternoon of estrus that seems to be related to plasma estradiol levels of estrus day, which might exert only a permissive role in this surge generation.     

Effects of third ventricular injection of beta-endorphin on luteinizing hormone surges in female rat: sites and mechanisms of opioid actions in the brain

The effects of third ventricular injection of beta-endorphin (beta-EP) on spontaneous, brain stimulation-induced and estrogen-induced LH surges were studied in the adult female rat. It was found that beta-EP blocked the preovulatory surge of LH release and ovulation, while it did not affect LH release in response to LH-RH injection. The site of the beta-EP blockade of ovulation was proved to be in the brain. Beta-EP completely blocked ovulatory LH release induced by the electrochemical stimulation of the medial amygdaloid nucleus and medial septum-diagonal band of Broca, but failed to block ovulation due to the stimulation of the medial preoptic area (MPO) or median eminence, though serum LH levels after the MPO stimulation were inhibited by beta-EP. In the spayed rats treated with estradiol benzoate (EB) on Day 1 and 4 of experiment, beta-EP given on Day 5 blocked the LH surge that normally occurred on that day and led to a compensatory surge of LH on the following day. Moreover, the LH surge on Day 5 was inhibited by beta-EP given either on Day 1 or Day 4. Present data suggest that beta-EP may act in inhibiting the preovulatory LH surges not only by suppressing the preoptic-tuberal LH-RH activities but also by affecting the initiation and development of stimulatory feedback of estrogen in the central nervous system.     

Preovulatory secretion of progesterone, luteinizing hormone, and prolactin in 4-day and 5-day cycling rats

Timing of ovulation and changes in plasma progesterone, luteinizing hormone (LH), and prolactin (PRL) during periovulatory stages were determined in Holtzman rats exhibiting regular 4- or 5-day cycles under a daily artificial illumination from 0500 to 1900 h. The 5-day cycling rats ovulated between 0130 and 0930 h on estrus, whereas some of the 4-day cycling animals ovulated as early as about 0130 h and others as late as 1130 h on estrus. Onset time of preovulatory LH and progesterone surges was about 1500 h on proestrus in both the 4- and the 5-day cycling rats. Peak levels of plasma LH and progesterone were measured at 1700 to 1900 h on proestrus, while the first rises and peak values of plasma PRL were evident a few hours earlier than those of plasma LH in the rats with two cycle lengths. Plasma LH levels at 1900 h on proestrus as well as plasma progesterone levels at 1600 and 2300 h on proestrus and at 0130 and 0330 h on estrus were significantly lower in the 5-day cycling rats than in the 4-day cycling animals (p less than 0.05). In contrast, PRL levels from 1500 through 2300 h on proestrus remained consistently higher in 5-day cycling rats than in 4-day cycling rats, and significant differences in PRL levels between these rats were apparent at 1500, 1600, and 2100 h (p less than 0.05-0.01). Thus, these results demonstrate that the 5-day cycling rats exhibit the attenuated magnitude of LH surge accompanied by the augmented preovulatory PRL release, and that plasma progesterone levels reflect the magnitude of LH surge. A tentative working hypothesis concerning the etiology of the 5-day cycle has been proposed.     

PACAP38 and PACAP27 administered intracerebroventricularly have an opposite effect on LH secretion

The effect of PACAP38 on the LH surge and ovulation was compared with that of PACAP27 and VIP in the same model. The peptides were administered intracerebroventricularly before the critical period of the proestrous stage. PACAP38 was able to inhibit ovulation and to prevent the preovulatory LH surge; however, PACAP27 did not inhibit the ovulation and VIP inhibited the ovulation in 2/11 animals. In those animals of the last two groups in which ovulation occurred, the preovulatory LH surge was higher than in control rats. It is speculated that the opposite effect of PACAP38 and PACAP27 on the preovulatory LH surge and ovulation is possibly mediated through different receptors.     

Luteinizing hormone requirements for ovulation in the rat.

Luteinizing hormone requirements for ovulation induction were studied in proestrous rats through detailed observation of the preovulatory surge, through various forms of LH injection under sodium pentobarbital blockade, and through estimation of LH uptake by the ovary. Blood LH levels in individual proestrous rats were obtained every 30 min and grouped according to their peak time (designated 0 h); mean LH levels higher than 7 and 5 ng/ml continued for 30 min and 2.5 h, respectively, the pituitary LH contents at 1400 and 2000 h on the day of proestrus were 2.1 and 0.7 micrograms, respectively, indicating that the amount of LH secreted during the surge was at least 1.4 micrograms. Single intravenous injections of 2 micrograms and 1 micrograms of pure rat LH (NIDDK-rLH-I-7; FSH and prolactin contaminations: 0.02% and less than 0.01%, respectively) to sodium pentobarbital-blocked rats induced ovulation in 4 out of 4 rats and 4 out of 6 rats, respectively, while 500 ng failed to induce ovulation in any (out of 7) rats. Two injections of 300 ng each with an interval of 20 min induced ovulation in 3 out of 8 rats, but if the interval was prolonged to between 30 and 120 min, 100% ovulation was obtained. Blood LH levels in these experiments indicated that a lower long-lasting LH level (about 5 ng/ml blood) is more important than a short, high level for ovulation induction. It was also shown that this level of LH could be given in separate doses if the interval was 30-120 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increase in ovulation rate after treatment of ewes with bovine follicular fluid in the luteal phase of the oestrous cycle

Administration of charcoal-treated bovine follicular fluid to Damline ewes twice daily (i.v.) from Days 1 to 11 of the luteal phase (Day 0 = oestrus) resulted in a delay in the onset of oestrous behaviour and a significant increase in ovulation rate following cloprostenol-induced luteolysis on Day 12. During follicular fluid treatment plasma levels of FSH in samples withdrawn just before injection of follicular fluid at 09:00 h (i.e. 16 h after previous injection of follicular fluid) were initially suppressed, but by Day 8 of treatment had returned to those of controls. However, the injection of follicular fluid at 09:00 h on Day 8 still caused a significant suppression of FSH as measured during a 6-h sampling period. Basal LH levels were higher throughout treatment due to a significant increase in amplitude and frequency of pulsatile secretion. After cloprostenol-induced luteal regression at the end of treatment on Day 12, plasma levels of FSH increased 4-fold over those of controls and remained higher until the preovulatory LH surge. While LH concentrations were initially higher relative to those of controls, there was no significant difference in the amount of LH released immediately before or during the preovulatory surge. These results suggest that the increase in ovulation rate observed during treatment with bovine follicular fluid is associated with the change in the pattern of gonadotrophin secretion in the luteal and follicular phases of the cycle.     

Human chorionic gonadotropin and luteinizing hormone-releasing hormone reverse the blockade of ovulation in pregnant mare's serum gonadotropin-primed immature rats by the anti-androgenic drug, hydroxyflutamide

The present study was designed to examine mechanism(s) of the anti-ovulatory action of the anti-androgen, hydroxyflutamide (OH-F). Prepubertal rats were treated with 4 IU pregnant mare's serum gonadotropin (PMSG) (day -2) to induce first estrus and ovulation. They received OH-F in sesame oil or oil alone at 08:00 and 20:00 h on day 0 (the day of proestrus) and ovulations were assessed on the morning of day 1. Eighty-three percent of control animals ovulated with a mean of 7.7 +/- 1.1 corpora lutea per rat. Hydroxyflutamide blocked ovulation in all but 2 of the 12 rats receiving this drug alone. All of OH-F treated rats that received 5 and 25 IU human chorionic gonadotropin (hCG) ovulated with means +/- SEM of 9.1 +/- 0.1 and 7.3 +/- 1.4 corpora lutea per rat, respectively. The dose of 0.2 IU hCG was essentially ineffective, while the effect of 1.0 IU hCG was intermediate. At the dose of 20 ng and above (100 and 500 ng) luteining hormone-releasing hormone (LHRH) completely overcame the ovulation blockade in the OH-F treated animals, while a 4-ng dose was ineffective. At 18:00 h on the day of proestrus, serum LH levels in control animals were 17.56 +/- 2.60 ng/mL, which were 920% above basal levels (1.90 +/- 0.13) indicating a spontaneous LH surge. This surge was suppressed in OH-F treated rats. Injection of LHRH, at the dose of 20 ng and above, reinstated the LH release in OH-F treated animals. Thus, the anti-androgen, OH-F, inhibits ovulation in PMSG-treated immature rats through its interference with the preovulatory LH surge; the inhibition can be reversed by hCG or LHRH. Hydroxyflutamide does not appear to interfere at the level of the pituitary, but may have direct action at the hypothalamic and (or) extrahypothalamic sites involved in the generation of positive feedback signals that control LH release.     

Effects of indomethacin on ovarian leukocytes during the periovulatory period in the rat

We have investigated the effects of indomethacin (IM), a non-steroidal anti-inflammatory drug, and the role of prostaglandins on the accumulation of leukocytes in the rat ovary during the periovulatory period. Adult cycling rats were injected sc with 1 mg of IM in olive oil or vehicle on the morning of proestrus. Some animals were killed at 16:00 h in proestrus. On the evening (19:00 h) of proestrus, IM-treated rats were injected with 500 micrograms of prostaglandin E1 in saline or vehicle. Animals were killed at 01:30 and 09:00 h in estrus. There was an influx of macrophages, neutrophils, and eosinophils into the theca layers of preovulatory follicles, and of neutrophils and eosinophils into the ovarian medulla from 16:00 h in proestrus to 01:30 h in estrus. All these changes, except the accumulation of neutrophils in the theca layers of preovulatory follicles, were blocked by IM treatment. At 09:00 h in estrus, large clusters of neutrophils were observed in IM-treated rats, around abnormally ruptured follicles. The accumulation of leukocytes was not restored by prostaglandin supplementation, despite the inhibition of abnormal follicle rupture and restoration of ovulation in these animals. These results suggest that different mechanisms are involved in leukocyte accumulation in the ovary during the periovulatory period, and that the inhibitory effects of IM on the influx of leukocytes are not dependent on prostaglandin synthesis inhibition.     

Evidence against a role of prolactin in the timing of ovulation in the turkey

Two separate experiments in which blood was sampled at 2-h intervals from turkeys hens failed to show a significant change in plasma prolactin (Prl) concentrations in relation to the preovulatory surge of luteinizing hormone (LH) for the first (C1) ovulation of a sequence. Intravenous injection of 125 IU of ovine Prl (NIH-P-S10) or of 1 or 2 ml of antiserum to turkey Prl at varying intervals before C1 ovulation had no effect on the timing or incidence of C1 ovulation. However, injection of Prl before C1 ovulation tended to inhibit ovulation of the second (C2) egg of the sequence, while injection of antiserum to Prl before C1 ovulation tended to either advance or inhibit C2 ovulation. Possibly, the effects of Prl and Prl antiserum on C2 ovulation reflect interference with maturation of the C2 ovarian follicle rather than interference with neuroendocrine processes that regulate the timing of the preovulatory surge of LH. The data for C1 ovulation argue against a change in circulating levels of Prl as a factor in the timing of the preovulatory surge of LH.     

Serotonin neuroleptics change patterns of preovulatory secretion of luteinizing hormone in rats

Serotonin receptor agonists or antagonists were used in this study to determine the timing and influence of serotonergic neurotransmission on phasic secretion of luteinizing hormone (LH). Daily injections of cyproheptadine (CP) or methysergide (MS), serotonin antagonists, initiated at 1600h on the day of vaginal proestrus, blocked the LH surge and ovulation. Vaginal smears remained cornified for 2–3 days. The drugs were ineffective when given at 0800h, though they terminated the LH surge prematurely when administered at 1730h. When quipazine, a serotonin receptor agonist was injected at 1400h or 2000h on proestrus, serum LH levels rose. This effect caused the LH surge to begin prematurely or to be sustained unusually long. Quipazine injected on diestrus 2 did not cause LH levels to rise, suggesting that its effect is estrogen dependent. Serotonin turnover in the hypothalamus was greater during onset of the LH surge than during its termination. When the LH surge was prolonged by exposing rats to light on proestrous evening, serotonin turnover remained high. The results of this study indicate that phasic secretion of LH on proestrus is accompanied by and may be dependent upon a period of serotonin neural activity.     

Modifications des cellules gonadotropes de la préhypophyse chez la ratte injectée de testostérone au cours du cycle oestral

Summary 4-day cyclic adult female Wistar rats were injected subcutaneously with testosterone propionate on diestrus 1 at 16:00 and on diestrus 2 at 10:00 respectively. Non-injected females served as controls. Autopsy was performed on diestrus 2 at 23:00, and on proestrus at 14:00 and 17:00 respectively. The blue Alcian-PAS staining was used to evidence FSH () and LH () pituitary cells.In control animals and in diestrus 2 injected females only a small number of FSH cells could be detected on diestrus 2 at 23:00. This number increased markedly on proestrus at 14:00 and decreased on proestrus at 17:00. A similar evolution was observed in diestrus 1 testosterone injected females, but the number of FSH cells appeared higher at any stage of autopsy in these females than in diestrus 2 injected females and in control rats.In control females, numerous LH cells were observed on diestrus 2 at 23:00. The number of these cells was diminished on proestrus at 14:00 and still more at 17:00. On the contrary few LH cells were detected in testosterone injected females on the evening of diestrus 2. An increase of these cells occurred on proestrus at 14:00, followed at 17:00 by only a weak diminution as established by comparison with control animals.An inhibition of FSH release and a suppression of the proestrus surge of LH were therefore supposed to cause, on one hand, the slowing up of follicular growth observed in diestrus 1 injected females and, on the other hand, the blockage of ovulation noted in both diestrus 1 and diestrus 2 treated animals.

Travail effectué avec l'aide de la D.G.R.S.T. Contrat n^o 72.7.0030.     

Blockade of the preovulatory release of gonadotropins and prolactin by spinal transections in female rats

The effect of spinal transections on the preovulatory release of gonadotropins and PRL was investigated in female rats. A preovulatory rise in serum LH, FSH and PRL and subsequent ovulation were prevented by complete spinal transections (CST) at high thoracic levels (T3-T7), but not at low thoracic and lumbar levels (T8-L5), performed at 1000-1230 h on proestrus. Norepinephrine (NE) concentrations in the preoptic-anterior hypothalamic area at 1700-1800 h on proestrus were also significantly reduced by CST at high thoracic levels, but not at lumbar levels. Either electrochemical stimulation of the suprachiasmatic part of the preoptic area or NE injection into the third ventricle at 1400-1500 h on proestrus restored ovulation in animals with CST at high thoracic levels. Animals with CST at lumbar levels exhibited relatively regular 4-day cycles, but those with CST at high thoracic levels showed prolonged periods of diestrous (8-20 days) before they resumed cyclicity. In the case of partial transections, bilateral transections of the lateral columns, but not transections of the dorsal or medial columns, of the spinal cord at T4-T5 significantly blocked the preovulatory gonadotropin release and the occurrence of ovulation. Unilateral transections of the lateral columns of the spinal cord or unilateral electrolytic lesions of the ventrolateral part of the medulla oblongata (VLMO) failed to block ovulation. When combinations of them were performed ipsilaterally, ovulation occurred, but when they were performed contralaterally, the incidence of ovulation was significantly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of gonadotropin-releasing hormone antagonists on serum follicle-stimulating hormone and luteinizing hormone under conditions of singular follicle-stimulating hormone secretion

Previous work has indicated that in long-term ovariectomized rats a potent antagonist to gonadotropin-releasing hormone (GnRH) suppressed serum luteinizing hormone (LH) more successfully than follicle-stimulating hormone (FSH). The present studies examined whether the rise in serum FSH which occurs acutely after ovariectomy, or during the proestrous secondary surge, depends on GnRH. In Experiment A, rats were ovariectomized at 0800 h of metestrus and injected with (Ac-dehydro-Pro1, pCl-D-Phe2, D-Trp3,6, NaMeLeu7)-GnRH (Antag-I) at 1200 h of the same day, or 2 or 5 days later. Antag-I blocked the LH response completely, but only partially suppressed serum FSH levels. Experiment B tested a higher dose of a more potent antagonist [( Ac-3-Pro1, pF-D-Phe2, D-Trp3,6]-GnRH; Antag-II) injected at the time of ovariectomy. The analog suppressed serum LH by 79% and FSH by 30%. Experiment C examined the effect of Antag-II on the day of proestrus on the spontaneous secondary surge of FSH, as well as on a secondary FSH surge which can be induced by exogenous LH. Antag-II, given at 1200 h proestrus, blocked ovulation and the LH surge expected at 1830 h, as well as increases in serum FSH which occur at 1830 h and at 0400 h. Exogenous LH triggered a rise in FSH in rats suppressed by Antag-II. In Experiment D proestrous rats were injected with Antag-II at 1200 h and ovariectomized at 1530 h. By 0400 h the antag had suppressed FSH in controls, but in the ovariectomized rats, a vigorous FSH response occurred.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interactions between 17 beta-estradiol and the hypothalamo-pituitary beta-endorphin system in the regulation of the cyclic LH secretion

This paper further substantiates the physiological role of beta-endorphin (beta-END) in the control of the cyclic LH secretion and provides new data on the interactions between 17 beta-estradiol (17 beta-E2) and beta-END at both the hypothalamic and pituitary levels. At the hypothalamic level, during the estrous cycle in rats, beta-END concentrations were highest on diestrus I in the arcuate nucleus, median preoptic area and median eminence and lowest at the time of the preovulatory 17 beta-E2 surge on proestrus, before the subsequent preovulatory hypothalamic GnRH and plasma LH surges. Data obtained in ovariectomized 17 beta-E2-treated ewes support the direct involvement of 17 beta-E2 in changes in beta-END and GnRH concentrations in these hypothalamic areas. At the anterior pituitary level, in vitro results obtained using anterior pituitaries from the proestrus morning cycling female rat have shown that 17 beta-E2 strongly suppresses beta-END secretion and that GnRH stimulates the release of beta-END. Furthermore, marked fluctuations were observed for plasma beta-END throughout the menstrual cycle in the woman. Low beta-END concentrations were observed in the period preceding the LH preovulatory surge. Taken together, these results show that: (1) decreases in hypothalamic beta-END concentrations, which are controlled at least by circulating levels of 17 beta-E2, modulate GnRH synthesis and/or release and contribute to the mechanisms which initiate the LH surge; (2) anterior pituitary beta-END might be involved in the mechanisms which terminate the LH surge.     

Role of progesterone in the modulation of the preovulatory surge of gonadotropins and ovulation in the pregnant mare's serum gonadotropin-primed immature rat and the adult rat

The role of progesterone in the regulation of the preovulatory surge in gonadotropins and ovulation was examined in this study by use of a potent antagonist of progesterone, RU 486 (17 beta-hydroxy-11 beta-[4-dimethyl-aminophenyl]-17 alpha- [prop-1-ynyl]estra-4,9-diene-3-one). The immature rat primed with pregnant mare's serum gonadotropin (PMSG) and the cycling adult animal were the models used to verify the role of progesterone. When RU 486 (200 micrograms/rat) was given as a single dose on the morning of proestrus, there was a significant reduction in the preovulatory surge levels of gonadotropins and ovulation in both animal models. Serum progesterone levels in both models at the time of death on the evening of proestrus were unaltered upon treatment with RU 486. RU 486 did not have any effect on gonadotropin levels in immature rats 7 days after castration. These results show that the actin of RU 486 on the preovulatory gonadotropin surge is due to an antagonism of the action of progesterone on the hypothalamic-pituitary axis. Thus, a role for progesterone in modulating the preovulatory surge of gonadotropins and, consequently, ovulation is strongly suggested.     

Differential regulation of preovulatory luteinizing hormone and follicle-stimulating hormone release by opioids in the proestrous rat

We have investigated the role of mu- and kappa-opioid receptors in the central control of preovulatory LH and FSH release in the proestrous rat. Animals were anesthetized with chloral hydrate at 14:00 h on proestrus day. Following femoral artery cannulation, they were mounted in a stereotaxic apparatus. Morphine and U-50488H (benzene-acetamide methane sulphonate) were infused intracerebroventricularly either alone or in combination with naloxone and MR1452, respectively. Controls received sterile saline alone. Blood samples were obtained at hourly intervals between 15:00 h and 17:00 h. Plasma LH and FSH levels were measured by radioimmunoassay. Morphine did not significantly change plasma LH levels at 15:00 h and 16:00 h sampling intervals. A significant increase was observed at 17:00 h compared to the controls (p<0.05). U-50488H significantly increased LH levels at 16:00 h and 17:00 h (p<0.05). The co-administration of naloxone and MR1452 with mu- and kappa-agonist had no significant effect on LH levels at any sampling interval. In all groups, LH levels showed a linear rise over the sampling period between 15:00 h and 17:00 h. None of the treatments significantly altered plasma FSH levels which however, declined towards the end of the afternoon surge. In conclusion, we suggest that the secretion of LH and FSH is differentially regulated by mu- and kappa-opioid receptors. It is thought that in all groups chloral hydrate interfered with the LH surge secretory systems.     

LH secretion around the time of the preovulatory gonadotrophin surge in the ewe

Blood samples were taken once an hour from 17 ewes starting on Day 15 of a natural oestrous cycle and continuing for 4 days or until 36 h after the onset of oestrus. On Days 12, 16, 17 and 18 of the cycle, blood samples were also taken every 5 min for 6 h, between 09:00 and 15:00 h. LH pulse frequency rose and amplitude fell between the luteal and follicular phase of the oestrous cycle ( ). In the period from 48 h before to 40 h past the peak of the preovulatory LH surge, LH pulse frequency did not change. LH pulse amplitude was similar prior to and following the LH surge. During the preovulatory LH surge, LH pulse amplitude rose markedly ( ), with the visible, discrete components of pulses ranging from twice to 20 times those seen prior to or following the surge. The amplitude of LH pulses on the downslope of the LH surge was greater than that on the upslope of the surge (P < 0.05). We conclude that the preovulatory LH surge may consist of an amalgamation of high frequency, high amplitude pulses of LH secretion.