Altered negative feedback response to ovariectomy and estrogen in prepubertal restricted-diet rats

Studies were conducted to explore the hypothesis that the delayed sexual maturation of female rats induced by reduced food intake (R) may result partially from an altered negative feedback response to estrogen. Animals were placed on 60% of normal food intake at 20 days of age. Controls (C) were fed ad libitum. Rats were used for three different experiments at 31-32 days of age. In Experiment I, rats were ovariectomized (OVX) and injected subcutaneously for 4 days with varying doses of estradiol benzoate (EB). They were killed the day after the last injection. In Experiment II, rats were ovariectomized and killed in groups at 4, 12, 24, 48, 72, and 120 h after OVX. In Experiment III, they were castrated and 1 wk later received a single injection of 0.5 microgram EB. Groups were killed at 1, 2, 4, 8, and 24 h after injection. Sera from all experiments were assayed for follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Results of Experiment I indicate that the efficacy of EB for suppressing LH, but not FSH, secretion is increased significantly in R rats. In Experiment II, OVX resulted in a delayed increase in serum LH, but not FSH, concentrations of R rats when compared to C animals. Results of Experiment III indicate a delayed, but more prolonged, suppression of LH secretion by EB in R rats when compared to C rats. Prolactin secretion, on the other hand, increased earlier in R rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of AMPA receptors inhibits prolactin and estradiol secretion and delays the onset of puberty in female rats

Previous experiments have evidenced the neuroendocrine role of AMPA receptors. Present studies were carried out to obtain information on the role of these receptors in the control of the onset of puberty. To this end, female rats were i.c.v. injected with vehicle or AMPA (agonist of AMPA receptors: 0.1 or 0.5 nmol/day) between 26 and 30 days (Experiment 1), or 30 and 34 days (Experiment 2) of age. Serum concentrations of PRL, LH and estradiol were measured before drug administration, 10 min after the last injection, at vaginal opening (VO) and at first estrus (FE) presentation. In both experiments, AMPA administration inhibited PRL and estradiol secretion without affecting LH release. When AMPA was administered between 26 and 30 days a significant delay in the day of vaginal opening was observed. These results confirmed the inhibitory effect of AMPA on PRL secretion and suggests a role of AMPA receptors in the control of puberty onset.     

Transitory increase in plasma FSH and LH levels induces early vaginal opening and corpus luteum formation in ovarian transplants of rats ovariectomized at 20 days of age

The effect of a transitory increase in plasma FSH and LH levels on puberty has been investigated. Hormonal changes were induced by bilateral ovariectomy (OVX) at 20 days of age followed by implantation of two ovaries (donor animals 20-day-old) beneath the kidney capsule 1, 2 or 3 days later. In an other group of animals the two interventions were made in reversed order. Rats in which OVX was made first showed early vaginal opening. If ovarian implantation preceded OVX, these two interventions did not affect the time of vaginal opening. More than 1/3 of the ovarian implanted animals exhibiting early opening of the vagina contained corpora lutea three days after vaginal opening. FSH and LH levels of OVX + ovary implanted rats were from the third day on following implantations markedly different from the OVX controls and were in the range of intact or sham-operated rats. The present findings indicate that a transitory increase in plasma gonadotropin levels around twenty days of age may lead to precocious puberty.     

Inhibition of estrogen facilitation of sexual behavior by the intracerebral infusion of actinomycin-D

It has been shown previously that intracerebral actinomycin-D (Act-D) pellets inhibit estrogen facilitated female sexual behavior, but it was not possible to test the reversibility of this effect. In the present study an attempt was made to distinguish between the possible temporary interruption by Act-D of the biochemical action of estrogen which facilitates sexual receptivity and permanent toxic effects of the drug. Act-D in saline was infused into the third ventricle or the preoptic area (POA) to determine whether a reversible suppression of sexual behavior as measured by the lordosis quotient (LQ) could be produced. Ovariectomized rats were implanted with midline guide tubes entering the third ventricle (eight rats) or with bilateral tubes extending to the corpus callosum above the POA (67 rats). Each animal served as its own control since pretest and Act-D and recovery tests were performed 10–14 days apart in most subjects. For each behavioral test implanted subjects were primed with 3μg estradiol benzoate (EB) and 0.5 mg progesterone (P) 48 hr later. Behavioral tests, each involving 50 mounts, were performed 4–6 hr after P. Following the pretest the animals were retested under experimental conditions. Inner cannulae were inserted into the POA through the guide tubes and 0.11 μg Act-D infused 24 or 12 hr before, simultaneously with, or 6, 12, 18, or 26 hr after EB. A recovery test was performed 10–14 days later with no intracerebral infusion. The control procedure (infusion of of saline either simultaneously with or 12 hr after EB) did not alter the LQ. Act-D infusion produced a reversible suppression of lordosis which was dependent upon the time of administration of Act-D. Intraventricular infusion of Act-D 6 hr after EB reversibly inhibited lordosis behavior and no lesions were produced. Act-D infused into the POA simultaneously with EB or 6 hr later reversibly suppressed the LQ. In the 6 hr group, for example, the LQ fell from 78.3 to 35.7, but 10–14 days later reached 74.3. Although brain lesions of varying extent were produced by Act-D, the marked but reversible suppression of lordosis behavior is consistent with the view that Act-D inhibits estrogen facilitation of lordosis behavior by means of a biochemical rather than cytotoxic action.     

Cytosol and nuclear estrogen receptor binding in the preoptic area and hypothalamus of female rats during pregnancy and ovariectomized, nulliparous rats after steroid priming: correlation with maternal behavior

In a previous study, high nuclear estrogen receptor concentrations in the preoptic area (POA) were found on Day 16 of pregnancy to prime females to respond to a subsequent low dose of estradiol benzoate (EB) after hysterectomy-ovariectomy by exhibiting maternal behavior in 48 hr. Receptor concentrations in the POA were found to be higher than those in the hypothalamus (HYP). The present study investigated when nuclear estrogen receptors increase during pregnancy in POA and when the difference in receptor concentrations between POA and HYP occurs. An attempt was made to reproduce these pregnancy changes with a 16-day treatment of estrogen and progesterone in ovariectomized (OVX), nulliparous rats. In Experiment 1, we measured cytosol and nuclear estrogen receptor concentrations in the POA and HYP of female rats during pregnancy. Nuclear receptor concentrations in the POA increased beginning on Day 10, increased again on Day 16, and continued at this high level for the remainder of pregnancy. Nuclear estrogen receptor concentrations in the HYP remained at a lower level throughout most of pregnancy until Day 22 when they increased significantly. In Experiment 2, we tested the maternal behavior and measured estrogen receptor concentrations in OVX, steroid-primed, nulliparous rats after hysterectomy (H) and EB treatment. While 90% of estradiol (E) + progesterone (P)-primed females displayed short-latency maternal behavior 48 hr after H and EB treatment, 46% of E + vehicle (V)-treated controls were maternal. At 0 hr (prior to H and EB treatment), there was a significantly larger nuclear receptor accumulation in the POA but significantly attenuated receptor binding in the HYP. P treatment significantly affected cytosol and nuclear estrogen receptor dynamics. Differences in nuclear estrogen receptor concentrations were shown to be based on the number of available binding sites and not to changes in receptor affinity for estradiol.     

Testosterone implanted in the preoptic area of male Japanese quail must be aromatized to activate copulation

Intracranial implantation of minute pellets of gonadal steroids was combined with aromatase inhibitor treatment to determine if aromatization within the preoptic area (POA) is necessary for androgens to activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, implantation of pellets of testosterone propionate (TP) or estradiol benzoate (EB) in the POA of castrated males restores male-typical copulatory behavior. In Experiment 1, adult male castrated quail were implanted intracranially with 200-micrograms pellets of equimolar mixtures of crystalline TP + cholesterol (CHOL), TP + 1,4,6-androstatriene-3,17-dione (ATD, an aromatase inhibitor), EB + ATD, or CHOL and behavior-tested with intact males and females. Copulation was stimulated by POA implants containing TP or EB (three of six CHOL + TP males and two of seven ATD + EB males copulated vs zero of four CHOL males), but copulation was not inhibited by combining ATD with TP (three of four ATD + TP males copulated). In Experiment 2, adult male castrated quail were injected systemically with ATD or oil for 6 days prior to and 14 days after intracranial implantation of 200-micrograms pellets containing the same amounts of TP or EB as in Experiment 1. The ATD injections completely blocked copulatory behavior in males with TP implants in the POA such that ATD/TP and Oil/TP mount frequencies differed significantly, but failed to block copulation in males with EB implants in the POA (proportions of males copulating were ATD/EB, 6/8; ATD/TP, 0/6; Oil/TP, 4/7). The cloacal foam gland, an androgen-sensitive secondary sex character, was unaffected by the dose of ATD used. We conclude that activation of copulatory behavior by TP implants in the POA is not due to nonspecific effects of high local testosterone concentrations but rather to aromatization. These results support the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to activation of male-typical copulatory behavior.     

Unilateral ovariectomy restores ovulatory cyclicity in rats with a polycystic ovarian condition

An acyclic polycystic ovarian condition can be induced in adult rats with a single injection of estradiol valerate (EV). The ovaries are small and contain multiple cystic follicles and no new corpora lutea. In the early stages of the condition, both basal plasma luteinizing hormone (LH) and LH responses to luteinizing hormone-releasing hormone (LHRH) are attenuated. Plasma androgens are indistinguishable from normal controls. The present study examines the effect of unilateral ovariectomy (ULO) on this condition. Removal of one cystic ovary results in almost immediate resumption of vaginal cyclicity that persists for at least 3 wk. At 1 or 3 wk after ULO the remaining ovary contains fresh corpora lutea, appears histologically normal, and is significantly heavier than the cystic ovary removed at ULO, indicative of compensatory hypertrophy. Despite the resumption of apparently normal cyclic function, basal plasma LH concentrations and LH responses to LHRH are not significantly better than those in intact animals with polycystic ovaries. Thus, the previously polycystic ovary is fully capable of normal ovulatory function despite obvious impairments in the hypothalamo-pituitary axis. Since ovulatory function resumes on a background of continued poor pituitary responsiveness, the primary defect, which ULO corrects, is probably at the hypothalamic level. Finally, the cystic ovary clearly contributes to the hypothalamic aberration to which it subsequently responds.     

Maturation of negative and positive estrogen feedback in the prepubertal female rat

The development of estrogen feedback system on gonadotropin release during sexual maturation in female rats was studied. Animals (Wistar strain rats) were divided into 6 groups according to their ages; 10, 15, 20, 25, 30, and 35 days. Both LH and FSH levels in serum increased significantly in response to ovariectomy in all age-groups studied when measured one week postoperatively, though in the rats aged 10-15 days the increase in FSH following castration was only slight. In rats older than 25 days, the postcastration gonadotropin rise, calculated as a percent increase from the basal figure, decreased gradually with increasing age. Ovariectomized rats injected with estradiol benzoate (EB, 5 micrograms/100 g BW) showed significantly lower levels of both LH and FSH than those in castrated controls. However, the inhibitory action of EB on postcastration gonadotropin output was found to be relatively less effective in rats older than 25 days. Ovariectomized rats primed with EB were again injected with a 2nd dose of EB (5 micrograms/100 g BW) at noon 3 days after priming. The 2nd EB injection induced a significant rise in LH 6 h later in 30- and 35-day-old, though not in younger, animals. On the other hand, the FSH response to EB was markedly enhanced during days 15-25 of age. These results indicate that the estrogen negative feedback action on gonadotropin release is already operating in female rats at a very early age, and that the brain sensitivity to estrogen decreases slightly during the late prepubertal phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

The reversible inhibition of steroid-induced sexual behavior by intracranial cycloheximide

Cycloheximide(Cyclo), an inhibitor of protein synthesis by a direct action on protein synthesis at the ribosomal level, was used to reversibly inhibit estrogen-induced sexual receptivity. Cyclo (100 μg per rat) was infused into the preoptic area(POA) of ovariectomized rats at varying times before, simultaneously with, and after 3 μg of subcutaneous estradiol benzoate (EB). All animals received 0.5 mg progesterone (P) 36 hr after EB, and were tested for sexual receptivity 4–6 hr after P. The females were placed with stud males and a lordosis quotient was computed for each female (lordosis quotient = number of lordosis responses/20 mounts by the male × 100). Females receiving Cyclo 6 hr before, simultaneously with, or 12 hr after EB showed significantly lower levels of sexual receptivity when compared to females receiving Cyclo 36 hr before and 18 and 24 hr after EB. When those animals that showed low levels of sexual behavior after Cyclo infusion were reprimed with EB and P 7 days later and presented with a male they showed high levels of sexual receptivity. Thus, the effect of Cyclo was reversible. Only Cyclo infusions into the POA (bilateral) and third ventricle were effective in suppressing sexual behavior. Caudate nucleus, lateral ventricle, and unilateral POA infusions were without effect.The data presented are in agreement with earlier work that utilized actinomycin D to inhibit steroid-induced sexual behavior. Cyclo was found to be less toxic than actinomycin D. All of the available evidence is consistent with the hypothesis that estrogen stimulates RNA and/or protein synthesis in its facilitation of sexual behavior in the female rat.     

Effect of estradiol benzoate and clomiphene on tyrosine hydroxylase activity and on luteinizing hormone and prolactin levels in ovariectomized rats

The effects of estradiol benzoate (EB) on tyrosine hydroxylase (TH) activity in the medial basal hypothalamus (MBH) and on plasma levels of luteinizing hormone (LH) and prolactin were studied in long-term ovariectomized rats. Administration of 10 μg EB produced significant elevation of TH activity on Days 1 and 3 following injection. LH levels were significantly lower than controls throughout the three day treatment period, although there was a significant increase from Day 1 to Day 2. TH activity and LH levels were inversely related throughout the experimental period. Clomiphene (15 μg/rat/day), a purported estrogen antagonist, was administered over a period of three days to control and EB-treated rats to determine whether the effect of EB on plasma LH levels was causally related to changes in TH activity. In rats receiving both EB and clomiphene, TH activity was lower and plasma LH was higher than after EB alone. The results support the hypothesis that the feedback effects of estradiol on LH release involve an action on the tuberoinfundibular dopaminergic (TIDA) neurons of the MBH and that clomiphene can oppose the inhibitory effect of estradiol on LH release by directly inhibiting TIDA neuron activity. Furthermore, EB-induced release of prolactin does not appear to involve detectable changes in the activity of TIDA neurons.     

Prenatal melatonin exposure influences the maturation of gonadotropin and prolactin estradiol-benzoate feedback system.

Gonadotropin and prolactin response to estrogen feedback in female rat offspring of control and melatonin treated (150 microg/100 g BW) mother rats during pregnancy (MEL-offspring) were studied at these periods: infantile, prepubertal and pubertal. In controls negative or absent LH feedback developed after estradiol benzoate (EB) injection up to 30 days of age indicating that the onset of puberty had not occurred. The positive feedback was established from day 33 on. However, in MEL-offspring the first activation of gonadotropin secretion during afternoon, 31 h after EB, was observed at 25 days of age, representing the first neuroendocrine sign of the onset of puberty. This positive response disappeared on day 30 in MEL-offspring. At 33 days of age, the LH positive response to EB was found in both groups, indicating a more advanced sexual development. In controls, this response increased at 35 days of age while in MEL-offspring it was highly depressed. FSH secretion in response to EB showed a negative feedback effect from infantile to the end of prepubertal period in both groups. The positive feedback was observed earlier in MEL-offspring (at 33 days of age) than in controls (at 35 days of age), but at this age it was absent in MEL-offspring. A positive prolactin response to EB at all ages in controls was observed. The typical pulsatility with higher values in the afternoon appeared by the first time at 30 days of age. However, in MEL-offspring no pulsatile response was observed throughout any age. These data suggest that prenatal melatonin administration altered gonadotropin and prolactin response to EB inducing precocious sensitivity during prepubertal period but depressed response during the pubertal period.     

Reappearance of cyclicity of vaginal smears in androgen-sterilized rats following thyroidectomy

During studies on the mechanism of hypersensitivity to gonadotropins of thyroidectomized rat ovary, results were obtained which suggest an increase in the endogenous luteinizing hormone (LH) release after thyroidectomy in androgen-sterilized rats. Female rats were injected subcutaneously with 1 mg of testosterone propionate dissolved in .05 ml of olive oil on Day 5 after birth. At the age of 10-12 weeks, those animals which showed persistent vaginal cornification were thyroidectomized. Within 1-2 days after thyroidectomy, the thyroidectomized rats exhibited leukocytic and epithelial vaginal smears for 2-6 days. Irregular cyclicity with the pattern of 2-6 days diestrus and 3-10 days estrus persisted for 1 month. Histological examination revealed that the corpora lutea were intermingled with a number of cystic follicles in the ovaries of the androgen-sterilized and throidectomized rats while the ovaries of androgen-sterilized controls had vesicular follicles but were devoid of corpora lutea. The results indicate a rapid enhancement in the LH release in androgen-sterilized rats following thyroidectomy.     

Mediation by gonadal steroids of plasma beta-endorphin and LH in castrated female and male rats

Immunoreactive beta-endorphin (IR-BE) was significantly decreased and luteinizing hormone (LH) significantly increased in female rats castrated for four weeks. Forty eight hours after a single injection of estradiol benzoate (EB), IR-BE levels increased, and LH levels were reduced. On the afternoon following the administration of a second injection of EB given six hours earlier, IR-BE levels were reduced below control values, whereas LH levels were significantly elevated. There was no change in IR-BE levels during the remainder of that afternoon whereas LH levels decreased over time. Similar to female rats, IR-BE was diminished and LH increased in castrated male rats. IR-BE was increased significantly above those values observed in intact animals 24 hr after a single injection of TP and returned to control levels by 48 hr after administration of TP. Injection of TP reduced LH to levels observed prior to castration. These findings suggest that gonadal steroids exert a feedback on the release of IR-BE from the pituitary of female and male rats opposite to their feedback effect on the release of pituitary gonadotropins.     

Length of progesterone exposure needed to resolve large follicle anovular condition in dairy cows

Hypothalamic unresponsiveness to an estradiol surge appears to be an underlying cause of large follicle anovular condition (follicular cysts), but progesterone exposure for 7 days resolves this condition. In this study, dairy cows with induced (Experiment 1) or naturally occurring (Experiment 2) follicular cysts were treated for different times with progesterone. In Experiment 1, 16 of 26 cows (62%) were induced into anovulation by causing a GnRH/LH surge when no ovulatory follicle was on the ovary. Anovular cows (n = 16) were assigned to one of four treatment groups ( 0, 1, 3, or 7 days of progesterone treatment) using an intravaginal, progesterone-releasing implant (CIDR). All anovular cows had low circulating progesterone concentrations before controlled internal drug releasing (CIDR) and greater concentrations that reached steady state (1.3 +/- 0.1 ng/mL progesterone) by 3 h after CIDR insertion. Circulating progesterone decreased to basal concentrations by 4 h after CIDR removal. Cows were treated with 5mg estradiol benzoate (EB) 12 h after CIDR removal. None (n = 4) of the control cows (0 day) had an LH surge after EB. All of the 3 days (5/5) and 7 days (4/4) CIDR-treated cows had an LH surge following EB, but only one of the 1 day (1/3) CIDR-treated cows. Magnitude of the LH peak was similar in the 3 and 7 days cows. All cows treated for 7 days ovulated (4/4), whereas, ovulation occurred in only 3/5, 1/3, and 0/4 of the cows treated for 3, 1, and 0 day, respectively. The two cows in the 3 days group that did not ovulate had a normal LH surge, but these two cows had a smaller maximal follicle size than cows that ovulated. In Experiment 2, naturally anovular lactating dairy cows (24 of 248) were identified using weekly ultrasonography. All anovular cows grew follicles to >12 mm, with 54% (13 of 24) having follicles larger than ovular size (15-24 mm) and 33% (8 of 24) having follicles that would be considered cystic (>25 mm). Anovular cows were randomly assigned to CIDR treatment for 0, 1, or 3 days. All (7/7) of 3 days, 33% (3/9) of 1 day, and 25% (2/8) of control (0 day) cows ovulated by 1 week after CIDR removal. Thus, 3 days but not 1 day of progesterone exposure appears to be sufficient to reinitiate estradiol responsiveness of the hypothalamus.     

GnRH induced LH release in suckled beef cows. II. The effects of exogenous corticoids and estradiol benzoate on luteinizing hormone release by GnRH

In Experiment 1, 24 suckled beef cows were assigned to 4 treatment groups (6 cows/group). Group I cows calved spontaneously. Parturition was induced in Groups 2, 3 and 4 with 20 mg dexamethasone (DEX) 8 to 12 days prior to expected calving date. Additionally, cows in Groups 3 and 4 received 8 mg triamcinalone acetonide (TA) 6 days prior to DEX treatment. Animals in Group 4 also received 10 mg estradiol benzoate (EB) with TA, and on alternate days until DEX, when 20 mg EB was given. Gonadotropin releasing hormone (GnRH, 100 mug) was given intramuscular (IM) to all cows on days 2 or 3 postpartum. Plasma LH increased (P< .05) following GnRH treatment in Groups 2, 3 and 4, but not in Group 1. LH release (area under the curve) following GnRH was greater (P< .05) for cows in Group 4 compared to cows in Groups 1, 2 or 3, and differences in LH release between Groups 1, 2 or 3 were not significant. In Experiment II, 36 mature Hereford cows were assigned to a 2 x 3 factorial experiment (6 cows/group). Groups 1 and 2, 3 and 5, and 4 and 6 received 0, 100, or 200 mug GnRH (IM) at 78 hr postpartum, respectively. In addition, cows in Groups 2, 5 and 6 received 5 mg EB at 36 hr postpartum. Plasma LH concentrations were not different (P <.05) among groups from 36 to 78 hr postpartum. A surge of LH in response to EB treatment was not detected at 54 to 62 hr (18 to 26 hr post EB), indicating a lack of response by the positive feedback mechanism at this early time postpartum. Mean plasma LH concentrations were elevated 78 to 82 hr postpartum for Groups 3 through 6. Treatment with EB at 36 hr caused a significantly greater (P< .05) response to GnRH with 200 mug of GnRH releasing more LH than 100 mug of GnRH.     

Activity of the hypothalamo-pituitary ovarian axis in hypothyroid rats with or without triiodothyronine replacement

The hypothalamic pituitary ovarian axis in adult female rats with 131-I induced hypothyroidism was studied before and after triiodothyronine (T3) replacement. Forty days after 131-I, hypothyroid (H) rats showed irregular cycles with predominantly diestrous vaginal smears, atrophied and underweight ovaries, and decreased serum T3, T4, LH and estradiol (E2). T3 replacement restored normal cycles and ovary weight and increased serum E2 levels above control values, while LH levels remained below the limit of detection of the RIA. The GnRH stimulation test performed on the day that the rats exhibited diestrous vaginal smears elicited a greater increase in FSH than in LH in H rats and a greater increase in LH than in FSH in both H-T3 treated and control rats. The data suggest that the lack of thyroid hormones in adult female rats seems to produce a reversion of sexual hormones to a prepubertal pattern, while T3 treatment restored normal estrous cycles and ovarian function.     

Estrogen induces estrus unaccompanied by a preovulatory surge in luteinizing hormone in suckled sows

The objective was to determine if progressive changes occurred in incidence of estrus and patterns of luteinizing hormone (LH) after estradiol benzoate (EB) administration at three stages of lactation. Estradiol benzoate (800 micrograms) was injected at the beginning of the second (7.8 +/- 0.3 days, range 7-8, n = 4), third (15.6 +/- 0.3 days, range 15-16 days, n = 5), or fourth (23.3 +/- 0.5 days, range 22-24, n = 4) wk of lactation. Interval to estrus (h) and proportion in estrus (in parentheses) were 72 (1/4), 88.5 (4/5), and 99 (4/4; pooled SEM = 3.5) for the second, third, and fourth weeks, respectively. Only one animal ovulated during lactation (third week). This animal had a progesterone concentration of 17 ng/ml 1 wk after estrus and an LH concentration above 2.0 ng/ml for 72 through 90 h after EB. In other sows, LH remained less than 1.0 ng/ml after EB. Patterns of LH after EB in sows treated during the fourth week of lactation were increased to a maximum of 0.76 ng/ml by 120 h after EB, which was greater than for those treated during the second or third week (maxima of 0.38 and 0.32 ng/ml, respectively; pooled SEM = 0.07; p less than 0.05). Concentrations of LH in sows that exhibited estrus were greater both before and after treatment than in sows that did not exhibit estrus after EB (p less than 0.05). By 2 wk after weaning, 8 sows had ovulated (6 of these exhibited estrus), and there were no effects of stage of lactation on these responses. We concluded that the behavioral responsiveness to EB increased as lactation progressed. The increased LH in sows treated during the fourth week indicated a partial recovery of the positive feedback response to EB. These data suggested that separate mechanisms caused behavioral and gonadotropin responses to EB in lactating sows.     

The effect of a special herbal tea on obesity and anovulation in androgen-sterilized rats

A special herbal tea has been used to treat clomiphene-resistant anovulatory disease and obesity effectively, especially in polycystic ovary syndrome (PCOS) cases with hyperinsulinemia. The effect of the herbal tea on obesity and anovulation was investigated in androgen-sterilized rats (ASR). The ASR model was established by subcutaneous injection of 1.25 mg testosterone propionate to Sprague-Dawley female rats at the age of 9 days. Rats were sacrificed around 112 days of age. ASR manifested with PCO, anovulation, high food intake, elevated body weight, and obesity. Immunocytochemistry demonstrated that estrogen receptors (ER) were predominantly distributed in the cytoplasm of neuropeptide Y (NPY)-containing neurons in the preoptic area (POA), and the coexpression was also found in the nuclei and fibers of NPY-synthesizing neurons in the arcuate nucleus (ARC). Compared with that in normal control rats, NPY expression was increased, the numbers of ER in hypothalamic ARC-median eminence (ME) decreased, gonadotropin-releasing hormone (GnRH) levels in ME was decreased, serum estrogen (E2) and leptin were elevated, and follicular stimulating hormone (FSH) and luteinizing hormone (LH) levels were reduced significantly in ASR. Significantly negative correlations between NPY and ER or GnRH, and between leptin and FSH or LH were observed. A positive correlation existed between serum leptin and body weight. These metabolic-endocrine changes in ASR were normalized after feeding the herbal tea. Both obesity and hypogonadotropin were expressed in ASR. The abnormal ovarian hormone milieu (elevated E2 levels) may have enhanced NPY expression and resulted in less GnRH and gonadotropin secretion. The herbal tea reduced body weight and induced ovulation in ASR.     

Catecholamine mechanisms in the feedback effects of estradiol benzoate on the release of LH and prolactin

The role of hypothalamic catecholamines and luteinizing hormone releasing hormone (LHRH) in the negative feedback effect of estradiol benzoate (EB) on luteinizing hormone (LH) release was studied in chronic ovariectomized rats. Administration of 10 micrograms EB decreased plasma LH levels and increased LHRH content in the medial basal hypothalamus (MBH) 1 day after injection. Inhibition of dopamine and norepinephrine synthesis with alpha-methyl-p-tyrosine (alpha-MT) reduced the LHRH content in the MBH in both oil- and EB-treated animals and partially reversed the decrease in plasma LH levels. Inhibition of norepinephrine synthesis with fusaric acid decreased LHRH content in both oil- and EB-treated rats but had no effect on plasma LH levels. The results suggest that at least a portion of the inhibitory effect of EB on LH release is due to the stimulation of an inhibitory dopaminergic mechanism which reduces LHRH release from the MBH. This feedback mechanism is apparently not susceptible to dopaminergic receptor blockade since administration of pimozide had no effect on LH levels. The stimulatory feedback effect of EB on prolactin release was studied in the same animals. alpha-MT and EB produced additive effects on plasma prolactin levels whereas fusaric acid blocked the EB-induced increase in plasma prolactin levels. Pimozide appeared to potentiate the effect of EB on prolactin release. The results reconfirm the possible role of noradrenergic neurons in the release of prolactin induced by EB and also suggest that EB stimulates a dopaminergic mechanism which is inhibitory to prolactin release but is normally masked by increased noradrenergic activity.     

Gonadotropin secretion during prolonged hyperprolactinemia: basal secretion and the stimulatory feedback effect of estrogen

Inoculation of cyclic female rats with the prolactin (Prl)/growth hormone-secreting pituitary tumor, MtT.W15, resulted in a cessation of estrous cyclicity within 5--10 days. Associated with this acyclicity was a persistently low serum concentration of estradiol and marked increases in both circulating Prl and progesterone. At Day 26 of acyclicity, basal serum luteinizing hormone (LH) values measured in samples taken every 20 min from 0900--1100 h were significantly reduced when compared to cyclic, nontumor animals on diestrus Day 2. There was no difference in basal follicle-stimulating hormone (FSH) concentrations. In a separate group of acyclic, tumor-bearing females 42--56 days after transplantation, a single s.c. injection of 20 micrograms estradiol benzoate (EB) at 1030 h elicited significant increases in both serum LH and FSH values between 1700 and 1830 h on the next day. The magnitude of the LH surge was reduced and that of FSH was increased in tumor-bearing animals when compared to cyclic, nontumor females given a similar EB injection on diestrus Day 1. These results demonstrate that chronic hyperprolactinemia is associated with inhibition of basal LH secretion and ovarian estrogen production and an increase in circulating progesterone concentrations. Nevertheless, the stimulatory feedback effects of estrogen on LH and FSH release are still present and functioning in acyclic female rats under chronically hyperprolactinemic conditions. These data suggest that the cessation of regular ovulatory cycles associated with hyperprolactinemia may be due to a deficiency of LH and/or estrogen secretion, but not to a lack of central nervous system response to the stimulatory feedback action of estrogen.