The acute stimulatory effect of estrogen on gonadotropin release in gonadotropin-releasing hormone-primed women

In order to prove the acute stimulatory effects of estrogen on pituitary gonadotropin release, we have performed the present experiments in 8 women with a hypergonadotropic state due to surgical castration or primary ovarian failure. They received gonadotropin releasing hormone (Gn-RH) for 12-21 h at the constant rate of 20 micrograms/h. In 5 of the women, estradiol-17 beta was concomitantly administered at the rate of 20 micrograms/h from 6 h after the start of Gn-RH infusion. Blood samples were collected frequently throughout the experiments for the analysis of LH, FSH and estradiol. In response to the sole stimulation of Gn-RH, remarkable and prompt rises in LH (313.5%), but to a lesser degree in FSH (194.2%), were observed within the initial 3 h, and their high levels were maintained throughout the experimental period. However, the additional administration of estradiol brought on a further sudden rise in both gonadotropins levels: 178.3% for LH and 163.5% for FSH within 2 h. These high levels were sustained during estradiol infusions. In 2 of them, blood samples were obtained for several hours after cessation of estradiol infusion. The circulating gonadotropin level dropped precipitously close to the baseline level within 3 h after estradiol infusions. Our data indicate that estrogen has an acute and strong augmentative effect on Gn-RH induced gonadotropin release in addition to its conventional negative and positive feedback effects.     

Site of negative feedback action of estrogen on gonadotropin secretion in normal women

We have reported that iv administration of conjugated estrogens results in no significant change in the plasma LH-RH level during the negative feedback phase of LH, suggesting that estrogen does not suppress LH by decreasing hypothalamic LH-RH. To determine the site of estrogen action during the negative feedback phase, we studied the pituitary response to a small amount of LH-RH after estrogen administration in normal cyclic women in the mid-follicular phase. The pituitary responses to an iv bolus of 2.5 micrograms of synthetic LH-RH were evaluated by measuring serum LH and FSH 2 h before and 8 h after administration of 20 mg of conjugated estrogens (Premarin). The mean levels of serum LH and FSH were significantly (p less than 0.05) decreased 8 h after the injection. The peak responses of LH and FSH to LH-RH were also significantly (p less than 0.05) reduced after Premarin administration. These findings suggest that the negative feedback effect of estrogen on gonadotropin secretion is caused by its direct suppression on the pituitary response to LH-RH.     

Differential effects of aging on estrogen negative and positive feedback

Recent studies have demonstrated an age-related decline in gonadotropins and a decrease in pituitary responsiveness to GnRH, indicating that aging influences the neuroendocrine components of the female reproductive axis independently of changes in ovarian function. To determine whether aging might also affect the luteinizing hormone (LH) negative and positive feedback responses to gonadal steroids, we administered a controlled, graded sex steroid infusion to 11 younger (45-56 yr) and nine older (70-80 yr) postmenopausal women (PMW) in whom endogenous ovarian steroids and peptides are uniformly low. The doses of estradiol (E(2)) and progesterone (P) were chosen to mimic levels across the normal follicular phase and have been shown previously to induce negative followed by positive feedback on LH. Similar E(2) and P levels were achieved in younger and older PMW (P = 0.4 and 0.3, respectively) and produced a biphasic LH response in all subjects. The early decline in LH to 53% of baseline was not different in older vs. younger PMW. However, the positive feedback effect was attenuated in older compared with younger PMW (peak LH 144.4 ± 19.5 vs. 226.8 ± 22.3 IU/l, respectively, P = 0.01). In conclusion, these studies in PMW demonstrate preservation of short-term steroid negative and positive feedback in response to exogenous E(2) and P with aging. Attenuation of positive feedback in older compared with younger PMW is consistent with previous reports of declining GnRH responsiveness with aging.     

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)     

A positive feedback effect of oestradiol on LH release in the male marmoset monkey, Callithrix jacchus.

Subcutaneous injections of oestradiol benzoate in oil, resulting in a sustained elevation of circulating oestradiol levels, induced an initial suppression of LH secretion, followed by a positive discharge of LH in castrated male and female and in intact male marmosets. Oestrogen-induced LH release (producing maximum LH concentrations 24 h after the injection) was observed in 75% of castrated males and females. A positive discharge of LH occurred in 50% of intact males 28-36 h after oestrogen administration.     

The effect of estrogen priming of hypogonadal women on the release of gonadotropins and prolactin in response to 2-hydroxyestradiol

We have previously shown that the administration of a 2-hydroxyestradiol (20H-E₂) infusion 9250 μg/h x 4 h) to hypogonadal women resulted in a selective increase in the levels of circulating prolactin (PRL) without changes in LH or FSH. The present study concerns the effect of estrogen priming of hypogonadal women on the release of gonadotropins and PRL in response to an identical 20H-E₂ infusion. Estrogen priming consisted of a 5 day course of orally administered ethinyl estradiol at a daily dose of 300 μg. Significant (P < 0.05) inhibition of LH release was observed within 1 h of the onset of the 20H-E₂ infusion reaching a nadir (?25 ± 2%) by 3.75 h. The circulating levels of FSH remained unaltered for the duration of the 8 h study. In contrast, significant (P < 0.05) increments in the release of PRL could clearly be detected after a lag period of 1.5 h reaching a peak (+91 ± 11%) by 4 h. These and previous findings demonstrate that the inhibitory influence of 20H-E₂ on gonadotropin secretion is conditional upon prior estrogen priming while the ability of 20H-E₂ to stimulate the release of PRL is not.     

Definition of estrogen receptor pathway critical for estrogen positive feedback to gonadotropin-releasing hormone neurons and fertility

The mechanisms through which estrogen regulates gonadotropin-releasing hormone (GnRH) neurons to control mammalian ovulation are unknown. We found that estrogen positive feedback to generate the preovulatory gonadotropin surge was normal in estrogen receptor beta knockout (ERbeta) mutant mice, but absent in ERalpha mutant mice. An ERalpha-selective compound was sufficient to generate positive feedback in wild-type mice. As GnRH neurons do not express ERalpha, estrogen positive feedback upon GnRH neurons must be indirect in nature. To establish the cell type responsible, we generated a neuron-specific ERalpha mutant mouse line. These mice failed to exhibit estrogen positive feedback, demonstrating that neurons expressing ERalpha are critical. We then used a GnRH neuron-specific Pseudorabies virus (PRV) tracing approach to show that the ERalpha-expressing neurons innervating GnRH neurons are located within rostral periventricular regions of the hypothalamus. These studies demonstrate that ovulation is driven by estrogen actions upon ERalpha-expressing neuronal afferents to GnRH neurons.     

Prenatal programming of reproductive neuroendocrine function: the effect of prenatal androgens on the development of estrogen positive feedback and ovarian cycles in the ewe

Exposure of the female ovine fetus to male hormones during a sensitive window of in utero life causes disruption to reproductive function. In some animals, androgen exposure completely abolishes reproductive cycles, but in others, cycles are progressively lost with age. The present study tested two predictions: that noncycling, androgenized animals are unable to respond to estrogen with a preovulatory-like surge of LH (estrogen positive feedback), and that the androgenized animals that exhibit a progressive loss of cycles also show a progressive loss of estrogen positive feedback. Androgenized ewes were generated by injection of their mothers with testosterone propionate twice per week from Day 30 to Day 90 of pregnancy (term, 147 days). Control ewes received no injections. Whether ewes could exhibit estrogen positive feedback was tested on five occasions before puberty (30 wk) and once during the anestrous period. All control animals had repeated reproductive cycles in both the first and second breeding season, and all showed robust LH surges during test periods. Despite the fact that 64% of androgenized animals showed reproductive cycles, estrogen positive feedback could be demonstrated in only 6.1% of trials. Subsequent experiments revealed that the lack of response to estrogen in androgenized animals was not because of pituitary insensitivity to GnRH, a requirement for higher concentrations of estrogen, or a surge that was delayed relative to the time of estrogen administration. The mechanisms by which some androgenized ewes can produce normal reproductive cycles in the apparent absence of estrogen positive feedback are currently unknown.     

Impaired LH-RH release by estrogen in women with sulpiride-induced hyperprolactinemia

The effects of hyperprolactinemia on the release of immunoreactive luteinizing hormone-releasing hormone (LH-RH) and luteinizing hormone (LH) in response to iv injection of 20 mg conjugated estrogens (Premarin) were studied. Five normal cycling women were injected with Premarin on the morning of the 7th day of the first cycle (control cycle), and then the plasma levels of LH-RH, LH, and prolactin (PRL) were determined every 8 to 16 hours for 72 h. Two months later, the same women received 200 mg of oral sulpiride daily for 8 days from the 3rd day of the cycle (sulpiride treated cycle), and then the same protocol as in the control cycle was applied. Mean (+/- SE) plasma levels of PRL on day 7 in the sulpiride treated cycle were significantly higher than those in the control cycle (118 +/- 24 ng/ml vs. 14 +/- 4 ng/ml, p less than 0.001). After estrogen injection, the mean percent increases in immunoreactive LH-RH at 32 h (control: 71 +/- 38% vs. sulpiride: 6 +/- 36%) and 40 h (154 +/- 38% vs. -5 +/- 21%) and in LH at the 48 h (175 +/- 89% vs. 57 +/- 57%) and 56 h (99 +/- 32% vs. 7 +/- 21%) were significantly (p less than 0.01 or p less than 0.05) suppressed in the sulpiride cycle. These data suggest that the impaired positive feedback effect of estrogen on LH-release in hyperprolactinemic anovulatory women may be caused, at least in part, by disturbed LH-RH release.     

Kainic acid lesioning of the preoptic area alters positive feedback of estrogen in prepubertal female rats

Stereotaxic infusion of kainic acid (KA) was performed to induce intrinsic neural lesions of the preoptic area (POA) in 25-day-old female rats. After KA infusion, rats in Experiment 1 received 10 micrograms of estradiol benzoate (EB) administered subcutaneously to assess positive feedback of EB on release of luteinizing hormone (LH) from the pituitary gland. Rats were perfused for light microscopic (LM) or electron microscopic (EM) evaluation of the lesion site. Rats of Experiment 2 were allowed to develop until the appearance of vaginal opening (VO) after which time vaginal lavages were taken to monitor the cyclicity of the vaginal epithelium. At 50 days of age, the right ovary from each rat was removed, trimmed of fat, and weighed. At 60 days of age, the remaining ovary was removed to assess compensatory ovarian hypertrophy (COH). In Experiment 3, we investigated the effects of POA/KA-infusion on sexual behavior. Sex behavior tests were conducted at 48 h after EB during the dark phase of the light cycle. In Experiment 1, all the control and saline-infused rats exhibited the expected rise of plasma LH two days after estrogen injection while the POA/KA-infusion abolished the positive feedback effect of EB on LH release. Ultrastructural examination of the lesion site revealed that neurons were undergoing acute degeneration while axons and afferent terminals seen in the same fields of analysis were morphologically intact. Preoptic area/KA lesions caused a marked delay in the appearance of VO. Duration of this temporal delay in POA/KA-lesioned rats was approximately 4 days, or one vaginal cycle. The lesioned animals showed normal compensatory hypertrophy after unilateral ovariectomy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biphasic stimulatory effects of estrogen on gonadotropin surges induced by continuous administration of gonadotropin-releasing hormone in women

The present experiments were performed to study the effects of preovulatory levels of estrogen on GnRH-induced gonadotropin release. Twelve female volunteers in various phases of the menstrual cycle received estradiol infusion for 66 h at a constant rate of 500 micrograms/24 h which is grossly equivalent to its production rate during the preovulatory follicular phase. In 8 of the women, GnRH was administered concomitantly from 6 h after the initiation of estradiol infusion. The administered doses of GnRH were 2.5 and 5 micrograms/h. Blood samples obtained throughout the infusion were analysed for LH, FSH, estradiol and progesterone. The sole administration of estradiol failed to induce the positive feedback effect on gonadotropin release within the experimental period in the early follicular phase (days 3-7) in 4 women. In 5 women treated during the follicular phase, remarkable LH releases were induced after a lag period by the infusion of both GnRH and estradiol. The induced LH surge formed a prolonged biphasic pattern. Although a similar pattern of FSH was observed in some cases, its response was minimal compared with that of LH. In 3 women during the luteal phase, however, a combined administration of estradiol and GnRH induced only a short term release of LH which was terminated in only 12 h. The present data indicate that 1) Preovulatory levels of estrogen affect the late part of the LH surge which is induced by constant administration of low doses of GnRH resulting in a prolonged biphasic release of LH, and 2) These effects of both hormones are not manifest in the presence of high levels of progesterone. These results indicate the possibility of a role of GnRH and estrogen in the mechanism of the prolonged elevation of a gonadotropin surge at mid-cycle.     

The feedback effects of sex steroid hormones on pituitary gonadotropin release in Turner's syndrome and Klinefelter's syndrome.

The present study was designed to elucidate the feedback relationship between the release of pituitary gonadotropins and sex steroid hormones in Turner's syndrome and Klinefelter's syndrome. LH-RH stimulation test was employed to evaluate the effects of sex steroids on the release of gonadotropins. The release of gonadotropins in response to LH-RH as well as in baseline level was suppressed after the treatment with estrogen (mestranol 0.08 mg/day) for 10 days, followed by the treatment of the same period with estrogen (mestranol 0.08 mg/day) and progesterone (chlormadinone acetate 2.0 mg/day) in combination in both syndromes. The inhibitory effect of the combined treatment was greater than that of the treatment with estrogen alone. Administration of testosterone propionate (25 mg/day) for 3 days resulted in suppression of the release of both gonadotropins in baseline level and in response to LH-RH in both syndromes, but the suppressive effect appeared to be less complete as compared with that of estrogen or estrogen-progesterone. It was thus verified that the feedback interaction between the pituitary gonadotropin release and sex steroids such as estrogen, estrogen-progesterone or testosterone was operative in the same fashion in the patients with Turner's syndrome and Klinefelter's syndrome.     

Effect of prenatal melatonin on the gonadotropin and prolactin response to the feedback effect of testosterone in male offspring

The purpose of this study was to investigate the effects of prenatal melatonin administration on the sensitivity of the androgens negative feedback effect on gonadotropin and prolactin secretion in male offspring. Male offspring of control (control-offspring) and melatonin treated (MEL-treated) (150 microg/100 g BW) mother rats during pregnancy (MEL-offspring), at infantile, prepubertal, and pubertal periods were studied. LH secretion in response to testosterone propionate (TP) in control-offspring showed the classical negative feedback effect at all ages studied. In MEL-offspring a negative response after TP was also observed in all ages studied although the magnitude of this response was altered in this group as compared to controls. FSH values were significantly lower at most ages and time points studied in MEL-offspring than in control-offspring. FSH secretion in MEL-offspring showed a delayed negative feedback action of TP injection as compared to control-offspring. This response was observed at 21 days of age in control-offspring and delayed until day 30 of life in MEL-offspring. Parallely it remain at later age in MEL-offspring than in control-offspring. Prolactin secretion in control-offspring showed increased values after TP injections from infantile to pubertal periods. This increase was blunted in MEL-offspring at 17 and 35 days of age showing significantly reduced (p<0.01; p<0.05) plasma prolactin levels. During pubertal period a prolactin positive response to TP administration was observed in MEL-offspring but with significantly lower magnitude than in control-offspring. These results indicate that prenatal melatonin exposure induced changes in the sensitivity of gonadotropin and prolactin feedback response to testosterone, indicating a delayed sexual maturation of the neuroendocrine-reproductive axis in male offspring.     

On feedback control of gonadotropin secretion

This note is an attempt to demonstrate that hypothalamic pulsatile GnRH secretion is not the result of a short-term, negative steroid hormone feedback. Clarification of this point is of importance for further modelling the control of gonads.     

On the evocability of a positive oestrogen feedback action on LH secretion in transsexual men and women.

In transsexual men with homosexual behaviour and intact testicular function, as well as in homosexual men with normal gender identity, following a negative oestrogen feedback effect a delayed positive oestrogen feedback action on LH secretion was evoked. By contrast, in transsexual men with hypo- or asexuality and intact testes or hypergonadotrophic hypo- or agonadism, as well as in heterosexual men with normal gender identity, a negative oestrogen feedback effect was not followed by a positive feedback action on LH release. In transsexual women with homosexual behaviour and oligo- and/or hypomenorrhoea, only a weak or at best moderate positive oestrogen feedback action on LH release was evocable, similarly as in castrated and oestrogen-primed heterosexual men. By contrast, in a transsexual woman with bisexual behaviour and eumenorrhoea, a strong positive oestrogen feedback action on LH secretion was evocable, as well as in heterosexual women with normal gender identity.