Variations in concentration of oxytocin and vasopressin in the paraventricular nucleus of the hypothalamus during the estrous cycle in rats

Oxytocin (OT) and arginine-8-vasopressin (AVP) were measured by radioimmunoassay in micropunched hypothalamic neurosecretory nuclei of estrous cycling female Sprague-Dawley rats. In the paraventricular nucleus (PVN): the concentration (pg/microgram protein) of OT was significantly higher in rats in diestrus than during proestrus, estrus, or metestrus, while the concentration during metestrus was significantly greater than in proestrus and estrus; the concentration of AVP was significantly lower in animals in estrus than during the other three stages; because the paraventricular OT levels dropped before proestrus, the AVP/OT ratio was significantly greater in animals in proestrus than in diestrus, metestrus, and estrus. In the supraoptic nucleus (SON) a similar trend was noted: the concentration of OT was highest during diestrus, and AVP was lowest during estrus, though neither was significantly different from other stages. Because the OT and AVP cycles in the SON were asynchronous, the ratio of AVP to OT was significantly higher in proestrus than in metestrus or diestrus and significantly greater in estrus than during diestrus. In contrast to these two areas, peptide concentrations did not vary significantly across the estrous cycle in other sites of nonapeptide synthesis, i.e. the anterior commissural nucleus (ACN) and the suprachiasmatic nuclei (SCN).     

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.     

Periovulatory changes in serum concentration and ovarian content of 5 alpha-androstane-3 alpha, 17 beta-diol in the adult rat

The high amounts of 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) present in immature female rats decline towards first ovulation, but on the day of first proestrus a peak is seen. This raises the possibility that during adulthood similar proestrous peaks may occur. Therefore, serum concentrations and ovarian content of 3 alpha-diol were estimated every two hours between 0900 and 2100 h in adult cyclic rats on the day of proestrus. In the same rats, serum concentrations of estradiol (E2), progesterone (P) and luteinizing hormone (LH) were measured, as were ovarian contents of E2 and P. A significant elevation in ovarian 3 alpha-diol was found between 0900 and 1700 h proestrus, whereas serum concentrations of 3 alpha-diol were elevated from 1300 to 2100 h. The high morning values of ovarian 3 alpha-diol correlated with those for ovarian E2 (p less than 0.005); the elevated serum concentrations of 3 alpha-diol during the afternoon correlated with serum P (p less than 0.005) and with serum LH concentrations (p less than 0.005). Serum and ovarian values were positively correlated for P and E2, but not for 3 alpha-diol. The rise in serum 3 alpha-diol could be prevented by blocking the LH surge with sodium pentobarbitone (Nembutal; 35 mg/kg b.w.) administered at 1300 h. In Nembutal-treated rats, the concentration of 3 alpha-diol at 1700 h (886 pg/ml) was significantly lower than in saline-treated control rats (1135 pg/ml; p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

Alterations in mast cell degranulation and ovarian histamine in the proestrous hamster

Mast cells in the ovary of cyclic hamsters were observed exclusively in the hilum and in the vicinity of blood vessels that enter and exit the ovary. Ovaries were collected on proestrus from hamsters at 0900 h preluteinizing hormone (LH) surge, 1500 h (peak LH surge), and 2100 h (post-LH surge) and processed for routine histologic staining with toluidine blue. A significant increase in the percentage of extensively degranulating mast cells was observed coincident with the gonadotropin surge (0900 h: 5.39 +/- 0.97%; 1500 h: 20.39 +/- 2.76%). At the peak of the LH surge the ovarian histamine concentration was also significantly higher than those before and after the surge (1500 h: 5.13 +/- 0.94 ng/mg ovary; 0900 h and 2100 h: 2.84 +/- 0.35 and 3.02 +/- 0.48 ng/mg, respectively). The results indicate that a major source of ovarian histamine may be mast cells residing in the ovarian hilum and surrounding the ovarian blood vessels that enter and exit the ovary. In addition, the gonadotropin surge on the day of proestrus may be a trigger for release of mast cell histamine.     

In vitro DNA synthesis by isolated preantral to preovulatory follicles from the cyclic mouse

In recent studies, we have shown that the smallest preantral follicles in the cyclic hamster increase DNA synthesis in the periovulatory period in response to surge levels of FSH. The current investigation was designed to determine whether the same phenomenon occurs in the cyclic mouse. Intact mouse follicles were isolated with watchmaker forceps (stages 4-6) or by enzymatic digestion (stages 1-4) at 0900 h and 1500 h on each day of the 5-day estrous cycle. The isolated follicles were classified into 6 stages: stages 1 and 2: follicles with 1 and 2 layers of granulosa cells; stage 3: follicles with 3 or more layers of granulosa cells and formation of theca; stages 4-6: incipient, small, and preovulatory antral follicles. The follicles at each stage were incubated for 3 h with [3H]thymidine. DNA content in stages 1-4 of follicles remained unchanged during the estrous cycle; for stages 5 and 6, DNA content was higher on the afternoon of proestrus than on other days of the cycle. Incorporation of [3H]thymidine for stages 1-3 (preantral follicles) started to increase at 1500 h of proestrus and peaked at 0900 h on estrus, whereas for stages 4-6, DNA synthesis peaked on proestrus (1500 h) and then fell by the morning of estrus. Thus, the rate of DNA replication in preantral and antral mouse follicles were different. Similarities and differences in folliculogenesis between mouse and hamster are discussed. These results suggest that DNA synthesis and the growth of all stages of follicles in the cyclic mouse may be associated with changing levels of periovulatory gonadotropins.     

Abdominal vagotomy decreased the number of ova shed and serum progesterone levels on estrus in the cyclic hamster.

The effects of abdominal vagotomy (AVGT) on ovarian function were studied in cyclic hamsters. AVGT significantly decreased the number of ova shed (AVGT: 10.5 +/- 1.5 ova/hamster, sham: 15.8 +/- 0.7 ova/hamster; P less than 0.05) and serum progesterone levels (AVGT: 2.1 +/- 0.3 ng/ml, sham: 3.9 +/- 0.7 ng/ml; P less than 0.05) on the morning of estrus. However, progesterone concentrations in the corpora lutea and non-luteal ovary on estrus in the AVGT and sham groups were similar. The serum estradiol levels in both groups on proestrus increased from 0900 h (AVGT: 75 +/- 10 pg/ml, sham: 72 +/- 6 pg/ml) to 1500 h (AVGT: 204 +/- 27 pg/ml, sham: 196 +/- 35 pg/ml) but there was no significant difference between the two groups. Partial degranulation of ovarian mast cells was not increased in the AVGT group. Also, vasoactive intestinal peptide (VIP) content in the ovary was not increased by AVGT at 0900 h on proestrus (AVGT: 60.1 +/- 16.8 pg/ovary, sham: 37.2 +/- 14.3 pg/ovary). These results indicated that AVGT interferes with normal ovulation and results in an increase in the number of atretic follicles, but that these effects by AVGT seemed not to be mediated through ovarian mast cells and VIP.     

Differential effects of RU486 and indomethacin on follicle rupture during the ovulatory process in the rat

Ovulation (i.e., the release of mature oocytes from the ovary) requires spatially targeted follicle rupture at the apex. Both progesterone and prostaglandins play key roles in the ovulatory process. We have studied follicle rupture and ovulation in adult cycling rats treated with a progesterone receptor antagonist (RU486), an inhibitor of prostaglandin synthesis (indomethacin, IM), or both. All rats were treated with LHRH antagonist on the morning (0900 h) of proestrus to inhibit endogenous gonadotropins and with 10 microg of ovine LH (oLH) at 1700 h in proestrus to induce ovulation. Animals were treated from metestrus to proestrus with 2 mg/day of RU486 or vehicle (olive oil) and on the morning of proestrus (1200 h) with 1 mg of IM or vehicle (olive oil). Some rats treated with vehicle or RU486 were killed on the morning of proestrus to assess preovulatory follicle development. The remaining rats were killed on the morning of estrus to study follicle rupture and ovulation. In vehicle-treated rats, oLH induced ovulation in 98% of follicles. In IM-treated rats, spatial targeting of follicle rupture was disrupted. Most oocytes were released to the ovarian interstitium (50%) or to the periovarian space (39%), and a smaller percentage (11%) of oocytes remained trapped inside the luteinized follicle. RU486-treated rats showed, on the morning of estrus, unruptured luteinized follicles. Only occasionally (2.8%), the oocytes were released to the periovarian space. IM treatment induced follicle rupture in RU486-treated rats, and 25% of oocytes were released to the ovarian interstitium. However, the number of oocytes released to the periovarian space (i.e., ovulated) was not increased by IM treatment in rats lacking progesterone actions. Overall, these data indicate that RU486 and IM have opposite effects on follicle rupture and suggest that both progesterone and prostaglandins are necessary for the spatial targeting of follicle rupture at the apex.     

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 induction of divergent gonadotropin secretion in vitro by variations in luteinizing hormone releasing hormone pulse regimen

The effects of luteinizing hormone releasing hormone (LHRH) pulse amplitude, duration, and frequency on divergent gonadotropin secretion were examined using superfused anterior pituitary cells from selected stages of the rat estrous cycle. Cells were stimulated with one of five LHRH regimens. With low-amplitude LHRH pulses (regimen 1) in the presence of potentially estrogenic phenol red, LH response in pituitary cells from proestrus 1900, estrus 0800, and diestrus 1,0800 were all significantly larger (P less than 0.05) than the other stages tested. In the absence of phenol red, responsiveness at proestrus 1900 was significantly larger than proestrus 0800, proestrus 1500, and estrus 0800 (P less than 0.01, 0.05, and 0.05, respectively); other cycle stages tested were smaller. No significant differences were observed between cycle stages for follicle-stimulating hormone (FSH) secretion in the presence or absence of phenol red. Because pituitary cells at proestrus 1900 were the most responsive to low-amplitude 4 ng LHRH pulses, they were also used to study the effects of LHRH pulses of increased amplitude or duration and decreased frequency. Increasing the amplitude (regimen 2) or the duration (regimens 3 to 5) increased FSH secretion; this effect was greatest with regimens 3 and 5. When regimens 3 and 5 were studied in pituitary cells obtained at proestrus 1500, FSH was significantly increased by both regimes, but most by regimen 5; furthermore, LH release was significantly reduced. When regimens 3 and 5 were studied in pituitary cells obtained at estrus 0800, FSH release was elevated most significantly by regimen 5. Thus, variations in LHRH pulse regimen were found to be capable of inducing significant divergence in FSH release from superfused anterior pituitary cells derived from specific stages of the estrous cycle.     

Prolactin secretion and its response to stress during the estrous cycle of the rats

Serum and pituitary prolactin (PRL) concentrations were measured during the estrous cycle of the rat with particular attention to the afternoons of the days of proestrus and estrus. Homogenizing machines, a Polytron and Sonifier, were used to extract PRL from the pituitary gland. The effects of ether anesthesia and restraint were also examined on the afternoons of both proestrus and estrus. The occurrence of a surge in PRL secretion during proestrus was confirmed with a peak at 1500 h, and this was accompanied by a decline in pituitary PRL content. A relatively high level of serum PRL was observed in the afternoon of estrus, during which time pituitary PRL content increased progressively. Ether anesthesia had no effect on the proestrus PRL surge, while restraint enhanced it. On the afternoon of estrus, restraint completely suppressed the rise in serum PRL, but ether anesthesia failed to suppress it completely. From these results, the following conclusions were drawn: 1) the PRL surge on the afternoon of proestrus occurs without synthesis of the hormone in the pituitary; 2) PRL secretion on the afternoon of estrus is accompanied by its synthesis in the gland; 3) the PRL response is distinct for each type of stress applied; and 4) PRL secretion is thus regulated by different mechanisms in proestrus and estrus.     

Characterization of cyclicity and hormonal profile with impending ovarian failure in a novel chemical-induced mouse model of perimenopause

4-Vinylcyclohexene diepoxide (VCD) causes early, gradual ovarian failure in mice because it specifically targets small pre-antral ovarian follicles. The period between loss of these follicles and ovarian failure is analogous to perimenopause in women. We sought to characterize the period of onset of ovarian failure in VCD-treated mice in regard to estrous cycle length and hormonal changes. Female C57Bl/6 mice (age, 28 days) were dosed daily for 15 days with VCD (160 mg/kg intraperitoneally) to cause early ovarian failure or with vehicle only (control animals). Cycle length was monitored by vaginal cytology. Plasma levels of 17beta-estradiol (E2), progesterone (P4), and follicle-stimulating hormone (FSH) in control and VCD-treated animals were measured during proestrus of cycles 1 through 12. Cycle length (mean, 5.8 days) did not differ between groups for cycles 1 through 4. In contrast, cycle length during cycles 5 through 12 was increased (mean length, 10.9 days; P < 0.05 versus control) in VCD-treated animals, which also showed an apparent increase in plasma FSH levels. Plasma E2 and P4 at proestrus did not differ between groups during any cycle. Ovarian failure in VCD-treated mice was confirmed by histological evaluation on day 156 after onset of dosing, whereas control animals were still cycling. Therefore, despite compromised cycle length in VCD-treated mice, peak ovarian steroid production in preovulatory follicles at proestrus is adequate. These results demonstrate that the VCD-treated mouse can serve as an appropriate model to mimic hormonal changes during the perimenopausal transition in women.     

小熊猫繁殖周期血清雌二醇和孕酮含量变化

为研究小熊猫繁殖周期血清雌二醇、孕酮含量变化规律,采用化学发光免疫分析法连续16 次测定了2只成体雌性小熊猫血清雌二醇和孕酮含量变化,历经发情间期、发情期和两次妊娠期;连续9次测定了7只小熊猫妊娠期的孕酮含量变化。结果:(1)发情间期,小熊猫血清雌二醇的水平一直维持在低水平(基础水平),进入发情前期,血清雌二醇水平明显升高,在发情期一直维持高水平,配种后迅速降至基础水平; (2)小熊猫血清孕酮含量在发情间期和发情期均维持在较低水平,直至发情期过后才出现升高,在妊娠期一直维持高水平,峰值出现在5 月;(3)发情的小熊猫不论妊娠与否,在妊娠期内血清孕酮含量均维持在高水平。研究表明:小熊猫血清雌二醇、孕酮含量变化能直接反映其繁殖规律,雌二醇对启动雌性小熊猫季节性繁殖起重要作用;在妊娠期内小熊猫血清孕酮含量升高不能作为判断小熊猫妊娠的标准;雌性小熊猫在妊娠期有假孕现象。     

Plasma gonadotropin,prolactin levels and hypothalamic tyrosine hydroxylase activity in rats during estrous cycle,after overiectomy and after blockade of catecholamine biosynthesis

Plasma gonadotropin, prolactin levels and hypothalamic tyrosine hydroxylase activity were evaluated at 0900, 1200 and 1700 h during diestrus, proestrus and estrus, ovariectomized and after systemic administration of reserpine or α-methyl p-tyrosine, which interfere with catecholamine biosynthesis, in rats. Gonadotropin and prolactin levels showed peak values during the afternoon of proestrus, while hypothalamic tyrosine hydroxylase activity was markedly lowered at 1200 on proestrus. Gonadotropin levels were slightly lowered whereas prolactin concentrations and hypothalamic tyrosine hydroxylase activity were significantly increased by reserpine. Depletion of hypothalamic dopamine by reserpine apparently resulted in significant elevation of prolactin levels which inturn induce tyrosine hydroxylase. Gonadotropin levels and hypothalamic tyrosine hydroxylase activity were significantly suppressed after the administration of α-methyl p-tyrosine. Prolactin levels, however, were elevated significantly. These results indicate that catecholamines are involved in the control of gonadotropin and prolactin release during estrous cycle and inhibition of catecholamines biosynthesis by α-methyl p-tyrosine could result in suppression of gonadotropin levels, whereas removal of tonic inhibition of hypothalamic dopamine by α-methyl-p-tyrosine elevate prolactin levels.     

The influence of exogenous progestin on the occurrence of proestrous or estrous signs, plasma concentrations of luteinizing hormone and estradiol in deslorelin (GnRH agonist) treated anestrous bitches

The objectives of this study were to confirm: (i) whether progestin treatment suppressed GnRH agonist-induced estrus in anestrous greyhound bitches; and (ii) the site of progestin action (i.e. pituitary, ovary). All bitches received a deslorelin implant on Day 0 and blood samples were taken from -1 h to +6 h. Five bitches were treated with megestrol acetate (2 mg/kg orally once daily) from -7 d to +6 d (Group 1) and 10 bitches were untreated controls (Group 2). Proestrous or estrous signs were observed in 4 of 5 bitches in Group 1, and 4 of 10 bitches in Group 2 (P = 0.28). The plasma LH responses (area under the curve from 0 to 6h after implantation) were higher (P = 0.008) in Group 2 than in Group 1. Plasma LH responses were similar (P = 0.59) in bitches showing signs of proestrus or estrus (responders) and in non-responders. The plasma estradiol responses (calculated as for LH response) were greater in Group 1 than in Group 2 (P = 0.048), and in responders than in non-responders (P = 0.02). In conclusion: (i) progestin treatment (a) did not suppress the incidence of bitches showing deslorelin-induced proestrus or estrus, and (b) was associated with a reduced pituitary responsiveness and an increased ovarian responsiveness to deslorelin treatment; (ii) the occurrence of proestrous or estrous signs reflected increased ovarian responsiveness to induced gonadotrophin secretion and not increased pituitary responsiveness to deslorelin.     

Effects of acute ovariectomy on anterior pituitary gland follicle-stimulating hormone and luteinizing hormone secretion in the metestrous rat

Changes at the anterior pituitary gland level which result in follicle-stimulating hormone (FSH) release after ovariectomy in metestrous rats were investigated. Experimental rats were ovariectomized at 0900 h of metestrus and decapitated at 1000, 1100, 1300, 1500, 1700 or 1900 h of metestrus. Controls consisted of untreated rats killed at 0900 or 1700 h and rats sham ovariectomized at 0900 h and killed at 1700 h. Trunk blood was collected and the serum assayed for FSH and luteinizing hormone (LH) concentrations. The anterior pituitary gland was bisected. One-half was used to assay for FSH concentration. The other half was placed in culture medium for a 30-min preincubation and then placed in fresh medium for a 2-h incubation (basal FSH and LH release rates). The basal FSH release rate and the serum FSH concentration rose significantly by 4 h postovariectomy and remained high for an additional 6 h. The basal FSH release rate and the serum FSH concentration correlated positively (r=0.71 with 72 degrees of freedom) and did not change between 0900 and 1700 h in untreated or sham-ovariectomized rats. In contrast, the serum LH concentration and the basal LH release rate did not increase after ovariectomy. Ovariectomy had no significant effect on anterior pituitary gland FSH concentration. The results suggest that the postovariectomy rise in serum FSH concentration is the result, at least in part, of changes which cause an increase in the basal FSH secretion rate (secretion independent of the immediate presence of any hormones of nonanterior pituitary gland origin). The similarities between the selective rises in the basal FSH release rate and the serum FSH concentration in the ovariectomized metestrous rat and in the cyclic rat during late proestrus and estrus raise the possibility that an increase in the basal FSH release rate may be involved in many or all situations in which serum FSH concentration rises independently of LH.     

Decreased luteinizing hormone-stimulated progesterone secretion by preovulatory follicles isolated from cyclic rats treated with the progesterone antagonist RU486.

Since administration of the antiprogesterone RU486 to cyclic female rats at metestrus and diestrus results in increased serum levels of LH, estradiol, and testosterone at proestrus, we investigated whether RU486 affects follicular steroidogenesis. Female rats with a 4-day estrous cycle, induced experimentally by a single injection of bromocriptine on the morning of estrus, were given RU486 (2 mg) twice daily (0900 and 1700 h) on metestrus and diestrus. At proestrus the preovulatory follicles were isolated and incubated for 4 h in the absence and presence of LH. In the absence of LH, accumulation of estradiol, testosterone, and progesterone in the medium was not different for RU486-treated rats and oil-treated controls. In contrast, LH-stimulated estradiol, testosterone, and progesterone secretions were significantly lower in RU486-treated rats compared with controls. Addition of pregnenolone to the incubation medium resulted in a significantly lower increase of progesterone in follicles from RU486-treated rats compared with those from oil-treated controls. This suggests that 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity is decreased by administration of RU486 in vivo. Aromatase and 17 alpha-hydroxylase/C17-20 lyase activities were not affected: addition of substrate (androstenedione and progesterone respectively) did not affect differently the amount of product formed (estradiol and testosterone) in RU486- and oil-treated rats. However, LH-stimulated pregnenolone secretion was lower in follicles from RU486-treated rats compared with follicles from oil-treated controls, suggesting that either cholesterol side-chain cleavage activity or LH responsiveness is decreased. At proestrus the preovulatory follicles from RU486- and oil-treated rats were not morphologically different.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 complete hypothalamic deafferentation on the estrous phase of follicle-stimulating hormone release in the cyclic rat

We investigated whether neural afferents to the medial basal hypothalamus play an acute role in the estrous phase of FSH release in the 4-day cyclic rat. A cannula was inserted into the right atrium of the heart under brief ether anesthesia during the early afternoon of proestrus for subsequent blood collections and injection of LHRH. In some of the rats, the medial basal hypothalamus was surgically isolated from the rest of the brain with a small knife under brief ether anesthesia between 2000 h and 2130 h of proestrus. Control groups consisted of naive rats which were not treated during the night of proestrus and sham-operated animals in which the knife was lowered to the corpus callosum between 2000 h and 2130 h or proestrus. Rats were bled at 2200 h of proestrus and at 0200 h, 0600 h and 1000 h of estrus for radioimmunoassay of plasma FSH and LH. The plasma FSH levels in all 3 groups between 2200 h of proestrus and 1000 h of estrus were elevated above levels observed in other cannulated rats bled to the onset of the proestrous phase of FSH release at 1400 h of proestrus. There were no statistically significant differences in plasma FSH or LH concentrations at any of the time periods between the 3 groups of serially bled rats. The deafferentation procedure did not appear to impair the pituitary gland's ability to secret gonadotrophins as injection of 50 ng of LHRH after the bleeding at 1000 h of estrus caused substantial elevations in plasma FSH and LH concentrations which were not different between the 3 groups. The results suggest that neural afferents to the medial basal hypothalamus play no acute role in the estrous phase of FSH release in the cyclic rat.     

Dynamics of messenger RNAs encoding inhibin/activin subunits and follistatin in the ovary during the rat estrous cycle

Quantitative changes in ovarian inhibin/activin subunit and follistatin mRNAs during the rat estrous cycle were examined by ribonuclease protection assay using digoxygenin-labeled RNA probes. Levels of ovarian inhibin alpha subunit mRNA remained low throughout estrus, metestrus, and diestrus; abruptly increased on the morning of proestrus; then rapidly decreased when the primary gonadotropin surge occurred. A similar changing pattern was observed in inhibin/activin beta(A) subunit mRNA. On the other hand, inhibin/activin beta(B) subunit mRNA showed a different changing pattern. Levels of beta(B) subunit mRNA remained constant during metestrus and diestrus, abruptly decreased on the afternoon of proestrus, then quickly recovered from the nadir by 1100 h on estrus. Throughout the rat estrous cycle, especially during the periovulatory period, alpha subunit mRNA levels were considerably higher than beta(A) and beta(B) subunit mRNA levels. In addition, changes in plasma concentrations of inhibin A and inhibin B were very similar to that in ovarian beta(A) and beta(B) subunit mRNA levels, respectively, with several-hour delays. These results suggest that levels of beta subunit mRNAs restrict secretion of dimeric inhibins. Levels of follistatin mRNA remained low from the midnight of metestrus to the midnight of diestrus, then increased until initiation of the primary gonadotropin surge. Thereafter, follistatin mRNA decreased, reached the nadir at 0200 h on estrus, then increased abruptly at 1100 h on estrus. Afterward, follistatin mRNA levels remained high until the morning of metestrus. The changing pattern of ovarian follistatin mRNA was similar to, and preceded, the changes in plasma concentrations of progesterone, suggesting that ovarian follistatin may modulate progesterone secretion during the rat estrous cycle.     

Relationship between the preovulatory luteinizing hormone (LH) surge and androstenedione synthesis of preantral follicles in the cyclic hamster: detection by in vitro responses to LH

Preantral follicles of cyclic hamsters were isolated on proestrus, estrus and diestrus I, incubated for 3 h in 1 ml TC-199 containing 1 microgram ovine luteinizing hormone (LH) (NIH-S22), and the concentrations of progesterone (P), androstenedione (A) and estradiol (E2) determined by radioimmunoassay. At 0900-1000 h on proestrus (pre-LH surge) preantral follicles produced 2.4 +/- 0.3 ng A/follicle per 3 h, less than 100 pg E2/follicle and less than 250 pg P/follicle. At the peak of the LH surge (1500-1600 h) preantral follicles produced 1.8 +/- 0.2 ng P and 1.9 +/- 0.1 A and less than 100 pg E2/follicle. After the LH surge (1900-2000 h proestrus and 0900-1000 h estrus) preantral follicles were unable to produce A and E2 but produced 4.0 +/- 1.0 and 5.0 +/- 1.1 ng P/follicle, respectively. By 1500-1600 h estrus, the follicles produced 8.1 +/- 3.1 ng P/follicle but synthesized A (1.6 +/- 0.2 ng/follicle) and E2 (362 +/- 98 pg/follicle). On diestrus 1 (0900-1000 h), the large preantral-early antral follicles produced 1.9 +/- 0.3 ng A, 2.4 +/- 0.4 ng E2 and 0.7 +/- 0.2 ng P/follicle. Thus, there was a shift in steroidogenesis by preantral follicles from A to P coincident with the LH surge; then, a shift from P to A to E2 after the LH surge. The LH/follicle-stimulating hormone (FSH) surges were blocked by administration of 6.5 mg phenobarbital (PB)/100 g BW at 1300 h proestrus. On Day 1 of delay (0900-1000 h) these follicles produced large quantities of A (2.2 +/- 0.2 ng/follicle) and small amounts of E2 (273 +/- 27 pg/follicle) but not P (less than 250 pg/follicle).(ABSTRACT TRUNCATED AT 250 WORDS)