Effects of thymulin and GnRH on the release of gonadotropins by in vitro pituitary cells obtained from rats in each day of estrous cycle

The effects of thymulin and GnRH on FSH and LH release were studied in suspension cultures of anterior pituitary cells from female adult rats sacrificed on each day of the estrous cycle. The spontaneous release of gonadotropins by pituitaries, as well as their response to GnRH or thymulin addition, fluctuated during the estrous cycle. Adding thymulin to pituitary cells from rats in diestrus 1 increased the concentration of FSH; while in cells from rats in estrus, FSH level decreased. Thymulin had a stimulatory effect on the basal concentration of LH during most days of the estrous cycle. Adding GnRH increased FSH release in cells from rats in diestrus 1, diestrus 2, or proestrus, and resulted in higher LH levels in cells obtained from rats in all days of the estrous cycle. Compared to the GnRH treatment, the simultaneous addition of thymulin and GnRH to cells from rats in diestrus 1, diestrus 2, or proestrus resulted in lower FSH concentrations. Similar results were observed in the LH release by cells from rats in diestrus 1, while in cells from rats in proestrus or estrus, LH concentrations increased. A directly proportional relation between progesterone serum levels and the effects of thymulin on FSH release was observed. These data suggest that thymulin plays a dual role in the release of gonadotropins, and that its effects depend on the hormonal status of the donor's pituitary.     

Abnormal estrous cyclicity after disruption of endothelial and inducible nitric oxide synthase in mice.

The roles of nitric oxide (NO) and nitric oxide synthase (NOS) in reproduction were studied by examining the estrous cycle of wild-type (WT) mice, inducible NOS (iNOS)-, and endothelial NOS (eNOS)-knockout mice. We observed an average estrous cycle of 4.8 +/- 0.2 days in WT mice. While we observed no significant influence of iNOS deficiency on cycle length, eNOS-knockout females showed a significantly longer estrous cycle (6.6 +/- 0.6 days; p < 0.03) than WT females, due to an extension of diestrus (p < 0.03). There was no influence of iNOS deficiency on ovulation rate compared with that in WT females; however, eNOS-knockout mice showed a significant reduction (p < 0.05) in ovulatory efficiency relative to WT or iNOS-knockout females. In contrast to WT females, in which the highest level of estradiol (E2) was observed at 1500 h of proestrus, iNOS-knockout females reached a peak of E2 at 1830 h of proestrus. In eNOS-knockout females, the peak of E2 occurred at 1830 h, as in iNOS-knockout mice; however, E2 levels were 5-fold and 3-fold higher (p < 0.05) than levels observed in WT and iNOS-knockout females, respectively. There was no effect of genotype on the plasma LH concentrations at proestrus. On the first day of diestrus, eNOS-knockout females showed significantly higher plasma E2 and progesterone levels (p < 0.05) relative to WT and iNOS-knockout females. The dysfunction in cyclicity, ovulation rate, ovarian morphology, and steroidogenesis in eNOS-knockout female mice strongly supports the concept that eNOS/NO plays critical roles in ovulation and follicular development.     

Actions of acetyl-L-carnitine on the hypothalamo-pituitary-gonadal system in female rats.

Acetyl-L-carnitine (ALC) is known to affect several aspects of neuronal activity. To evaluate the neuroendocrine actions of this compound, several endocrinological parameters were followed in ALC-treated and control animals during recovery from dark-induced anestrus. In treated animals, serum luteinizing hormone (LH) and prolactin levels were higher than those of controls during the proestrous and estrous phases of the cycle, and serum estradiol levels were higher during estrus. No significant changes were observed in serum levels of follicle-stimulating hormone and progesterone. Uterine weight was increased in ALC-treated rats during proestrus and estrus, but not in diestrus. The basal release of gonadotropin-releasing hormone (GnRH) from perifused hypothalamic slices of ALC-treated animals was elevated at proestrus and diestrus, and GnRH release elicited by high K+ was higher during all three phases of the cycle. The basal release of LH from perifused pituitaries of treated animals was elevated in diestrus, and the LH response to GnRH was higher in estrus and diestrus I. Depolarization with K+ caused increased LH secretion during proestrus and estrus in treated animals. In contrast to these effects of ALC treatment in vivo, no direct effects of ALC were observed during short- or long-term treatment of cultured pituitary cells. These results indicate that ALC treatment influences hypothalamo-pituitary function in a cycle stage-dependent manner, and increases the secretory activity of gonadotrophs and lactotrophs. Since no effects of ALC on basal and agonist-induced secretory responses of gonadotrophs were observed in vitro, it is probable that its effects on gonadotropin release are related to enhancement of GnRH neuronal function in the hypothalamus.     

Anterior pituitary leptin expression changes in different reproductive states: in vitro stimulation by gonadotropin-releasing hormone.

This study was designed to learn more about the changes in expression of rat anterior pituitary (AP) leptin during the estrous cycle. QRT-PCR assays of cycling rat AP leptin mRNA showed 2-fold increases from metestrus to diestrus followed by an 86% decrease on the morning of proestrus. Percentages of leptin cells increased in proestrus and pregnancy to 55-60% of AP cells. Dual labeling for leptin proteins and growth hormone (GH) or gonadotropins showed that the rise in leptin protein-bearing cells from diestrus to proestrus was mainly in GH cells. Only 10-20% of leptin cells in male or cycling female rats coexpress gonadotropins. In contrast, 50-73% of leptin cells from pregnant or lactating females coexpress gonadotropins and only 19% coexpress GH, indicating plasticity in the distribution of leptin. Leptin cells expressed GnRH receptors, and estrogen and GnRH together increased the coexpression of leptin mRNA and gonadotropins. GnRH increased cellular leptin proteins three to four times and mRNA 9.8 times in proestrous rats and stimulated leptin secretion in cultures from diestrous, proestrous, and pregnant rats. These regulatory influences, and the high expression of AP leptin during proestrus and pregnancy, suggest a supportive role for leptin during key events involved with reproduction.     

Circadian clock mutation disrupts estrous cyclicity and maintenance of pregnancy

Classic experiments have shown that ovulation and estrous cyclicity are under circadian control and that surgical ablation of the suprachiasmatic nuclei (SCN) results in estrous acyclicity in rats. Here, we characterized reproductive function in the circadian Clock mutant mouse and found that the circadian Clock mutation both disrupts estrous cyclicity and interferes with the maintenance of pregnancy. Clock mutant females have extended, irregular estrous cycles, lack a coordinated luteinizing hormone (LH) surge on the day of proestrus, exhibit increased fetal reabsorption during pregnancy, and have a high rate of full-term pregnancy failure. Clock mutants also show an unexpected decline in progesterone levels at midpregnancy and a shortened duration of pseudopregnancy, suggesting that maternal prolactin release may be abnormal. In a second set of experiments, we interrogated the function of each level of the hypothalamic-pituitary-gonadal (HPG) axis in order to determine how the Clock mutation disrupts estrous cyclicity. We report that Clock mutants fail to show an LH surge following estradiol priming in spite of the fact that hypothalamic levels of gonadotropin-releasing hormone (GnRH), pituitary release of LH, and serum levels of estradiol and progesterone are all normal in Clock/Clock females. These data suggest that Clock mutants lack an appropriate circadian daily-timing signal required to coordinate hypothalamic hormone secretion. Defining the mechanisms by which the Clock mutation disrupts reproductive function offers a model for understanding how circadian genes affect complex physiological systems.     

Gonadotropin-releasing hormone binding sites in ovaries of normal cycling and persistent-estrus rats

The gonadotropin-releasing hormone (GnRH) binding capacity in ovaries and pituitaries of normal cycling rats at different stages of the estrous cycle and in ovaries of persistent-estrus rats was measured using radioligand-receptor assay (RRA). Persistent estrus was induced either by neonatal administration of testosterone propionate (1.25 mg s.c.) on the second day of life or by a hypothalamic suprachiasmatic frontal cut made with Halász' knife. All animals were killed during the critical period (1400-1600 h), and GnRH receptor was assayed. GnRH receptor levels in both ovaries and pituitaries changed during the estrous cycle. The total number of ovarian GnRH binding sites was significantly higher in proestrus than in diestrus 1, the stage in which the lowest level was found. When binding sites were expressed in fmol/mg ovary, the highest level was observed in diestrus 2; however, no changes were observed during the estrous cycle when GnRH binding sites were expressed as fmol/mg protein. Changes noted were very similar to those demonstrated in pituitary GnRH receptors in our present and previous experiments. Higher levels of pituitary binding sites were found in diestrus 2 and proestrus than in estrus and diestrus 1. The changes in the GnRH receptor levels were more striking in the pituitary than in the ovaries. It appears that the total number of ovarian GnRH binding sites was not altered in either of the two persistent-estrus groups, but that their concentration was significantly higher (expressed in fmol/mg ovary or fmol/mg protein) than on any day during the estrous cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of paradoxical sleep deprivation on estrous cycles of the female rats

The present purpose was to examine how sleep deprivation affects the estrous cycle of the female rat. Paradoxical sleep-deprived (PSD) adult female Wistar rats were compared to home-cage control (CTRL) on their estrous cyclicity. Forty-four PSD and forty-four CTRL female rats were distributed into 4 subgroups of 11 animals each according to the phase of estrous cycle and were subjected to sleep deprivation for 96 h by the multiple platform technique. After PSD period, vaginal estrous cycles were taken for an additional 9 days. Animals that were submitted to PSD in diestrus phase (PSD-diestrus) had their estrous cycles disrupted during the recovery period by showing a constant diestrus during the first week. As for hormone alterations, progesterone concentrations were statistically higher in PSD-diestrus compared to respective phase control and to PSD-proestrus and PSD-estrus rats while CTRL-metestrus had higher levels than CTRL-proestrus and estrus groups. Testosterone was significantly decreased in PSD-estrus in relation to PSD-proestrus and PSD-diestrus groups and was lower in CTRL-diestrus rats than in home-cage rats in proestrus. In addition, PSD-diestrus phase exhibited higher concentrations of corticosterone and lower estrogen than the respective control rats. These data indicate that PSD may modulate the ovarian hormone release through alterations in hormonal-neurochemical mechanisms.     

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.     

A Mathematical Model for the Actions of Activin,Inhibin, and Follistatin on Pituitary Gonadotrophs

The timed secretion of the luteinizing hormone (LH) and follicle stimulating hormone (FSH) from pituitary gonadotrophs during the estrous cycle is crucial for normal reproductive functioning. The release of LH and FSH is stimulated by gonadotropin releasing hormone (GnRH) secreted by hypothalamic GnRH neurons. It is controlled by the frequency of the GnRH signal that varies during the estrous cycle. Curiously, the secretion of LH and FSH is differentially regulated by the frequency of GnRH pulses. LH secretion increases as the frequency increases within a physiological range, and FSH secretion shows a biphasic response, with a peak at a lower frequency. There is considerable experimental evidence that one key factor in these differential responses is the autocrine/paracrine actions of the pituitary polypeptides activin and follistatin. Based on these data, we develop a mathematical model that incorporates the dynamics of these polypeptides. We show that a model that incorporates the actions of activin and follistatin is sufficient to generate the differential responses of LH and FSH secretion to changes in the frequency of GnRH pulses. In addition, it shows that the actions of these polypeptides, along with the ovarian polypeptide inhibin and the estrogen-mediated variations in the frequency of GnRH pulses, are sufficient to account for the time courses of LH and FSH plasma levels during the rat estrous cycle. That is, a single peak of LH on the afternoon of proestrus and a double peak of FSH on proestrus and early estrus. We also use the model to identify which regulation pathways are indispensable for the differential regulation of LH and FSH and their time courses during the estrous cycle. We conclude that the actions of activin, inhibin, and follistatin are consistent with LH/FSH secretion patterns, and likely complement other factors in the production of the characteristic secretion patterns in female rats.     

Expression of ghrelin in the porcine hypothalamo-pituitary-ovary axis during the estrous cycle

Ghrelin, a 28-amino acid acylated peptide produced mainly by the stomach, has various functions. Recent studies focus on its endocrine and/or paracrine effects in the regulation of the hypothalamo-pituitary-gonadal axis, that is, the role in reproduction. Previous data have shown that variation of ghrelin depended on the phases of estrous cycle in adult rat ovary. This study was to investigate the expression of ghrelin in the cyclic porcine hypothalamo-pituitary-ovary axis and stomach by semiquantitative RT-PCR and immunohistochemical method. Twenty virginal gilts were classified into four groups as the proestrus, estrus, diestrus1 and diestrus2. Results showed that expression of ghrelin mRNA in the hypothalamus changed with the estrous cycle, i.e., with the highest level in the proestrus and the lowest in the estrus. In the pituitary, the pattern of ghrelin mRNA expression during estrous cycle markedly decreased in the estrus and diestrus1. In the ovary, ghrelin mRNA exhibited with the highest level in the diestrus2 and the lowest in the proestrus, which was different from those in the hypothalamus and pituitary. In the stomach, the expression of ghrelin mRNA had the same tendency as that of the porcine ovary. In immunohistochemical experiment, ghrelin immunoreactive cells were predominantly located in the luteal compartment and growing follicles in the luteal phase of ovary. However, only few ghrelin immunoreactive cells were found in the proestrus ovary. In gastric mucosa, ghrelin immunoreactive cells were detected in the estrus, diestrus1 and diestrus2, but few ghrelin positive cells were seen in the proestrus. Results suggest that ghrelin may play a major role in the endocrine network that integrates energy balance and reproduction.     

Prepubertal treatment with estrogen or testosterone precipitates the loss of regular estrous cyclicity and normal gonadotropin secretion in adult female rats

To examine the effects of prepubertal steroid environment on subsequent estrous cyclicity and gonadotropin secretion, Silastic implants containing 25, 50 or 100% 17 beta-estradiol (E2;n=34), 50% diethylstilbestrol (DES; n=16) or 50% testosterone (T; n=17) were placed into female rats at 12 days of age and removed on the day of vaginal opening (18-24 days of age). At 80 days of age, the percentages of regularly cycling females in the E2-(three groups combined), DES- and T-implanted groups were 59%, 0% and 59%, respectively. By 110 days of age, the percentages were reduced to 24%, 0% and 0%, and at 140 days of age 6%, 0% and 0%, respectively. Many of these females displayed irregular estrous cycles followed by a persistent estrous (PE) state. By contrast, 89% of the control females (blank implants or no implant) maintained regular cycles up to 140 days of age. At 150 days of age, an i.p. injection of gonadotropin-releasing hormone (GnRH; 100 ng/100 g BW) markedly increased serum luteinizing hormone (LH), but not follicle-stimulating hormone (FSH), in intact PE females treated prepubertally with E2 implants. After the test with GnRH, PE rats were ovariectomized (OVX). Thirty days after OVX, similar GnRH administration significantly increased serum levels of both LH and FSH, but these responses were significantly (P less than 0.01) reduced when compared with those in OVX controls. Progesterone administration to estradiol benzoate-primed, acutely (3 days) OVX, or long-term (43 days) OVX-PE females did not increase LH or FSH release. These results indicate that exposure to exogenous estrogen or T prior to puberty precipitates the decline in estrous cyclicity associated with the loss of gonadotropin surge response, presumably due to an alteration in hypothalamic GnRH release.     

Sex and estrous cycle-dependent differences in glial fibrillary acidic protein immunoreactivity in the adult rat hippocampus

Sex differences in the morphology and function of the hippocampus have been reported in several species, but it is unknown whether a sexual dimorphism exists in glial fibrillary acidic protein (GFAP) expression in the rat hippocampus. We analyzed GFAP immunoreactivity in the hippocampus of intact adult male rats as well as in females during diestrus and proestrus phases of the estrous cycle. We found that in CA1, CA3, and dentate gyrus, GFAP immunoreactivity was higher in proestrus females as compared with males and diestrus females. In CA1, a similar GFAP immunoreactivity was found in males and in diestrus females, but in dentate gyrus, males presented the lowest GFAP content. Interestingly, differences in astrocyte morphology were also found. Rounded cells with numerous and short processes were mainly observed in the hippocampus during proestrus whereas cells with stellate shape with few and long processes were present in the hippocampus of males and diestrus females. The marked sex and estrous cycle-dependent differences in GFAP immunoreactivity density and in astrocyte number and morphology found in the rat hippocampus, suggest the involvement of sex steroid hormones in the sexually dimorphic functions of the hippocampus, and in the change in its activity during the estrous cycle.     

Effects of the intensity of the suckling stimulus and ovarian steroids on pituitary gonadotropin-releasing hormone receptors during lactation

These studies examined whether the decrease in pituitary responsiveness to gonadotropin-releasing hormone (GnRH) observed during lactation in the rat results from a change in pituitary GnRH receptors. GnRH binding capacity was determined by saturation analysis using D-Ala6 as both ligand and tracer. During the estrous cycle, the number of GnRH binding sites increased from 199 +/- 38 fmol/mg protein on estrus to 527 +/- 31 fmol/mg protein on the morning of proestrus, whereas there was no change in receptor affinity (Ka, 6-10 X 10(9) M-1), During lactation, females nursing 8 pups on Days 5 or 10 postpartum had 50% fewer GnRH receptors (109-120 fmol/mg protein) than observed during estrus or diestrus 1 (199-242 fmol/mg protein) although receptor affinity was similar among all the groups. No deficits in pituitary GnRH receptors were observed in females nursing 2 pups on Day 10 postpartum. Removal of the 8-pup suckling stimulus for 24 or 48 h resulted in a dramatic increase in GnRH receptor capacity by 24 h from 120 +/- 16 to 355 +/- 39 fmol/mg protein. The rise in GnRH receptors after pup removal was accompanied by an increase in serum luteinizing hormone (LH) and estradiol concentrations. To assess the role of ovarian steroids in determining GnRH receptor capacity during lactation, females were ovariectomized (OVX) on Day 2 postpartum. Suckling of a large litter (8 pups) completely blocked the postcastration rise in serum LH and in pituitary GnRH receptors on Day 10 postpartum (OVX+ 8, 77 +/- 12 fmol/mg protein; OVX+ 0, 442 +/- 38 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)     

Male and female genotype mediate pheromonal regulation of the mouse estrous cycle

Estrous cyclicity was studied to examine the possibility that strain differences in the regularity of the mouse estrous cycle are the result of different olfactory signals produced by the male. Females with regular estrous cycles (lines E and S1) were housed in the olfactory presence of males from a line with irregular cycles (line CN-) or in the presence of males of their own line (used as a control). Females with irregular cycles (line CN-) were housed in the presence of males from a line with regular cycles (line E) or were exposed to males of their own line. The regularity of the estrous cycle decreased in line E females (regular cycles) when exposed to line CN- males (irregular cycles). The decreased regularity of line E cyclicity resulted from an increased period of diestrus, i.e., lengthening of the cycle. In contrast, line S1 females (regular cycles) did not show any change in estrous cyclicity when exposed to line CN- males. The period of diestrus increased in line CN- females when they were exposed to line E males. These results provide evidence that 1) the genotype of the male can influence the regularity of the estrous cycle, and 2) the genotype of the female regulates her responsiveness to environmental factors (e.g., male odor).     

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.     

Prolactin receptors in the rat mammary gland. Change during the estrous cycle

Ovine prolactin (o-PRL) binding to mammary gland membranes was studied during the estrous cycle in the rat. Groups of rats were decapitated throughout the 4-day estrous cycle at 10 h00 on the days of diestrus I, diestrus II and estrus and at 10 h00, 12 h00, 16 h00 during the day of proestrus. Daily vaginal smears were taken to determine the stage of the estrous cycle which was also controlled by PRL and LH serum levels. Prolactin receptors were quantified in the 100 000 g pellet. For one Scatchard analysis, mammary gland membranes from 5 animals were pooled. Results given are the mean of 4 or 5 pools. Results obtained showed that the apparent affinity constant (KA) remained unchanged during the days of diestrus II and at all the times studied of proestrus and showed a slight but significant decrease on the days of estrus and diestrus I (or metestrus). The binding capacity did not vary from the day of diestrus II to the proestrus 16h00 (11.3 +/- 2.8 fmoles/mg protein) but sharply increased on the day of estrus (190.4 +/- 35.9 fmoles/mg protein). Binding capacity remained elevated on the day of diestrus I. This increase of PRL receptors on the day of estrous would appear to be an important step in preparing mammary gland for pregnancy and lactation.     

Puberty and ovulatory release of gonadotropins in spontaneously hypertensive rats

The age at vaginal opening, estrous cyclicity, serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) on the day of proestrus, and number of ova and ovarian weight as measured on the day of estrus in spontaneously hypertensive (SH) and genetically matched normotensive Wistar Kyoto (WKY) female rats were compared. In SH rats, there was a significant delay in the vaginal opening, but the regular 4-day estrous cycle followed afterwards. No significant changes were observed in the afternoon increase in serum LH, FSH and PRL on the day of proestrus in SH and WKY rats, although the basal levels of LH and PRL in the morning (11:00 h) were lower in SH rats than in WKY rats. The mean number of ova in SH rats was also less than in WKY rats, whereas the ovarian relative weight was similar in both species of rats. It can be said that SH rats undergo certain, but not critical, endocrine and/or neuroendocrine changes related to reproduction.     

Ovarian steroidogenic enzyme activities during the rat estrous cycle

We have correlated the concentrations of serum LH, estradiol and progesterone with the activities of 2 ovarian steroid biosynthetic enzymes during the rat estrous cycle. Ovarian 3 β-hydroxysteroid dehydrogenase isomerase (3-βHSD) activity decreased from 29 ± 6 nmol/mg protein/ min (mean ± SEM) in diestrus, to 7 ± 0.4 nmol/mg protein/min in late proestrus (p < 0.005), and subsequently increased to 36 ± 9 nmol/mg protein/min in metestrus (p < 0.01). Ovarian 17-hydroxylase (17-OH) activity decreased from early to late proestrus (3.3 ± 0.2 vs 2.2 ± 0.2 nmol/mg protein/min, p <0.0025), and subsequently increased to 3.9 ± 0.2 in metestrus (p<0.001). Serum LH, estradiol and progesterone peaked during proestrus, and reached a nadir during estrus. We conclude that the activities of 3-βHSD and 17-OH in the rat ovary vary markedly during the estrous cycle. These changes may underlie the pattern of steroid secretion characteristic of this process.     

Does corpus luteum function autonomously during estrous cycle in the rat? A possible involvement of LH and prolactin

This study examined the of LH and prolactin in the control of corpus luteum function during 4-day cycles in the rat. Bromocriptine (BRC) treatment was performed on proestrus or/and estrus morning that means before or after the preovulatory release of LH. This caused complete blood prolactin depression from the time of injection until diestrus 1 afternoon. This decrease in blood prolactin concentration was associated with a rise in the tonic level of LH secretion in those females which received BRC as soon as on proestrus. We first observed that injection on the morning of proestrus of doses of BRC capable of blunting prolactin secretion on proestrus afternoon did not significantly impair the preovulatory release of LH and did not prevent ovulation occurring during the following night. The life span of the corpora lutea edified from ovarian follicles rupturing before or under BRC administration did not exceed that of those formed under physiological circumstances since 4-day cycles culminating in ovulation constantly took place in all the treated animals whatever the time of BRC injection. To determine the pattern of luteal activity in the absence of prolactin secretion, we measured blood progesterone concentration from estrus until late diestrus in female rats injected with BRC on proestrus and/or estrus at 1100 h. The initiation of the function of corpus luteum on estrus and the achievement of its full activity on diestrus 1 did not appear to be affected by BRC. By contrast the level of blood progesterone declined more rapidly on the morning of diestrus 2 in BRC-treated than in control females. The capacity for autonomous progesterone secretion by corpus luteum of the cycle was discussed in the light of previous and present observations.     

Effect of estrus cycle, ovariectomy and lactation on variations of basal corticosterone levels or agression stress levels in rats]

In the Rat, the estrous cycle induces a rhythm of plasmatic corticosterone level : the fluctuations of basal or stress corticosteronemy are significantly superior during the periods of high estradiol secretion, proestrus and estrus, that during metaestrus and diestrus. Ovariectomy, performed at 60 days of age, is without effect on resting corticosteronemy, but reduces significantly the response to stress. Weaning unaffects the basal level of plasmatic corticosterone which remains comparable to diestrus level ; however, stress response decreased during lactation returns to normal level at the end of the first ovarian cycle (diestrus).