Estrogen Positive Feedback Research Articles

Endocrinological analysis of hypothalamic primary amenorrhea (author's transl)

Primary amenorrhea, in which serum concentrations of gonadotropins are low or normal, has been considered to be relatively rare. Recent analysis in our outpatient clinic revealed that the incidence of hypothalamic primary amenorrhea is higher than previously appreciated, comprising 26.7% of the total primary amenorrheas. Endocrinological functions of the hypothalamo-hypophyseo-ovarian axis in these patients were therefore investigated. Studies on gonadotropin secretion indicated that a disturbance in LH-RH secretion and a lack of estrogen positive feedback were principle features of this disease. In addition to the dysfunction of gonadotropin secretion, the control of PRL secretion was disturbed in this disease since there was a poor PRL response to chlorpromazine in spite of normal responsiveness to TRH. Thus, "isolated gonadotropin deficiency" hitherto used to describe this disease is not pertinent. Furthermore, these results suggest that PRL might be involved in the onset of puberty in humans. Clinically, the induction of ovulation with HMG (Human Menopausal Gonadotropin) is possible in hypothalamic primary amenorrhea, although the ovarian responsiveness to gonadotropin is poor. Therefore, an endocrinologically precise diagnosis of hypothalamic primary amenorrhea is important in the gynecological clinic because fertility has been considered to be almost impossible in primary amenorrhea.

Pulsatile pituitary gonadotropin secretion during maturation of the dominant follicle in monkeys: estrogen positive feedback enhances the biological activity of LH.

In the follicular phase of the menstrual cycle, pulsatile patterns of LH and FSH secretion in monkeys change during maturation of the dominant follicle. At the preovulatory surge, the most striking event is the prodigious elevations of bioassayable LH, rising up to 50-fold within 24 h. Principally, establishment of the surge is due to marked enhancement of the amplitude of LH secretory pulses. In contrast, LH and FSH measured by RIA enter, in parallel, the surge modes of secretion approximately 5 h later than bioassayable LH and rise more slowly; the B:I ratio may reach 10:1. This same disparity between bioassayable versus immunoassayable LH was induced in castrate monkeys under estrogen positive feedback stimulation. We conclude that the preovulatory estrogen surge promotes the secretion of an LH molecule(s) having enhanced biological activity.

Luteinizing Hormone- and α-Subunit-Secreting Pituitary Tumor: Positive Feedback of Estrogen*

Gonadotropin-secreting pituitary tumors have rarely been reported in eugonadal patients. A 30-yr-old man, sexually potent, with normal-sized testes, but azoospermic, presented with a pituitary tumor documented by an enlarged sella turcica and an intrasellar mass by pneumoencephalography and computerized tomography. Testicular biopsy demonstrated marked Leydig cell hyperplasia and decreased spermatocyte maturation. The plasma LH level was elevated at 207 mlU/ml (normal, 6–26 mlU/ml), but the FSH level was low at 2 mlU/ml (normal, 5–25 mlU/ml). Plasma testosterone was elevated at 1500 ng/dl (normal, 300–1000 ng/dl); othergonadal steroids were also increased in the circulation, i.e. 5α-dihydrotestosterone, androstenedione, estradiol, and 17α-hydroxyprogesterone. The α-subunit was markedly elevated at 72 ng/ml plasma (normal, <0.5 to 2.5 ng/ml). The molar plasma α-subunit to LH ratio was 2.8, whereas normal or hypogonadal subjects have ratios less than 1. After 100 μg LRH iv, there was an increase of plasma L...

Rapid recovery of estrogen-induced pituitary gonadotropin surges after luteectomy in rhesus monkeys

In the presence of a functional corpus luteum, positive estrogen feedback on the surge modes of gonadotropin secretion is blocked in rhesus monkeys. We investigated the effects of luteectomy (Lx) on the time required for recovery of pituitary responsiveness (LH/FSH surges) to positive estrogen feedback. Estradiol-17β-3- benzoate (EB, 50μg/kg sc) was given: 1) 24h prior to, 2) the day of, or 3) 24 h after luteal ablation. Daily measurements of serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17β (E 2) and progesterone (P) were made on each monkey for 5 days. Serum P fell to undetectable levels within 24 h after Lx, whereas E 2 levels in circulation peaked within 24h after injection of EB. Among early follicular phase monkeys, this EB treatment results in typical midcycle type LH/FSH surges within 48h. Lx alone was not soon followed by significant changes in pituitary gonadotropin secretion. When circulating P levels were undetectable the pituitary responded fully to EB; that is, typical midcycle type FSH/LH surges occurred. When serum P was in the midst of declining after Lx, gonadotropin surges were present, but attenuated. However, when P levels remained elevated for more than 24 h after EB injection, the surge modes of FSH/LH secretion remained fully blocked. These results demonstrate that the suppressive influence of luteal secretions (principally progesterone) on positive estrogen feedback regulation of the surge modes of pituitary gonadotropin secretion is quite transient in these primates.

Plasma FSH, LH, the positive feedback of oestrogen, ovulation and luteal function in the ewe given bromocriptine to suppress prolactin during seasonal anoestrus.

The effects of pharmacological reduction of the high plasma prolactin concentration typical of seasonal anoestrus in sheep were assessed with respect to positive feedback of oestrogen on LH release, ovulation, and progesterone secretion. Treatment of 16 Scottish Blackface ewes with 1 mg bromocriptine, i.m. twice daily for 12 days, reduced prolactin concentrations in peripheral plasma from 64 +/- 10 ng/ml before treatment to < 4 ng/ml. This treatment had no effect on the proportion of ewes discharging LH and FSH in response to 12.5 microgram oestradiol benzoate (3/8 before compared with 5/16 during treatment) or the proportion of ewes ovulating in response to oestrogen treatment. Plasma progesterone concentrations remained low even in ovulating ewes. It is concluded that treatment with bromocriptine alone is unlikely to restore oestrous cycles to ewes in seasonal anoestrus.

Hormonal steroids, neurotransmitters and sexual differentiation of the brain

Male rats castrated on the first day of life exhibit preference of sexual responsiveness to partners of the same sex following oestrogen or androgen treatment in adulthood. Thus, in genetic males a female differentiated brain is activated postpubertally not only by oestrogens but also by androgens, resulting in female-like behaviour. On the other hand, females injected with androgen during perinatal life showed predominantly male behavior following castration and androgen treatment in adulthood. Furthermore, in males castrated on the first day of fife and later implanted with ovaries, a corpus luteum inducing positive oestrogen feedback on LH-secretion could be observed, whereas perinatally androgenized females lost the capability of cyclic gonadotrophin secretion. From numerous experiments involving androgens, oestrogens and anti-androgens it was concluded that sex hormones may act as “teratogens” if present in nonphysiological concentrations during critical organization periods of the brain, leading to permanent disorders of sexual behaviour or gonadotrophin secretion associated with permanent structural alterations in discrete brain regions. Recent studies demonstrated that neurotransmitters, which may be regarded as local hormones of the brain, can exert similar “teratogenic” effects if present in nonphysiological concentrations and/or turnover rates during brain differentiation. Treatment of newborn male rats with psychotrophic drugs, such as pargyline, reserpine or pyridostigmine, known to affect concentrations and/or turnover rates of neurotransmitters in the brain, induced permanent changes of sexual behaviour associated with permanent structural and/or biochemical changes in the brain. In females, onset of puberty, cyclicity and sexual behaviour were also altered following neonatal neurodrug administration. Recently, Ward reported on diminished male and increased female sexual activity in male offspring of rats having been exposed to stress during pregnancy. Following ACTH administration during pregnancy as well as after prenatal stress we found significantly decreased testosterone levels in the plasma of newborn male rats. There is an increasing number of findings suggesting similar mechanisms of brain differentiation possibly to be operative in the human.

Gonadotropin Insufficiency in Patients with Thalassemia Major*

To elucidate whether the cause of sexual maturational arrest in thalassemia major is of hypothalamic or pituitary etiology, three female and two male patients were extensively studied. After the iv administration of 150 micrograms gonadotropin-releasing hormone (GnRH) and 500 micrograms of TRH, all patients demonstrated a minimal LH and no FSH response, with variable PRL and TSH responses. The test was repeated after the patients received 100 micrograms GnRH im daily for 7 days. The LH, FSH, PRL, and TSH responses were similar to those obtained previously. The female patients were then retested twice, after priming with 17 beta-estradiol (2 mg daily for 7 days) and again after treatment with human menopausal gonadotropins. The male patients were treated with hCG and, after testosterone reached normal adult male values, the GnRH-TRH stimulation test was repeated. In both the female and male patients, the pituitary responses remained unchanged. These results demonstrate the presence of primary gonadotropin insufficiency as well as the lack of positive estrogen feedback mechanism in patients with thalassemia major. The site of this abnormality has been demonstrated to be the pituitary gland, since hemosiderosis of the pituitary without hypothalamic involvement has been found at autopsy in one patient.

Investigation and Management of Symptomatic Hyperprolactinaemia

Fifteen patients with infertility and hyperprolactinaemia have been investigated using tests of prolactin and LH secretion, and treated by prolactin suppression. In addition, 4 patients with hyperprolactinaemia not desiring fertility were also investigated. Of the total group, 16 had galactorrhoea and 15 had amenorrhoea. Pituitary tumours were present in 6 patients and 4 had pituitary microadenomas. Prolactin levels measured by both radioimmunoassay and radioreceptor assay were elevated before treatment and fell during therapy with bromoergocryptine (7.5 mg daily). Tests of prolactin release with TRH and chlorpromazine before treatment did not distinguish patients with functional hyperprolactinaemia from those with pituitary tumours. Basal plasma gonadotrophin concentrations were not elevated despite subnormal urinary oestrogen levels. The serum LH response to LRH was normal during hyperprolactinaemia, but LH release in response to oestrogen provocation was impaired in 14 of 17 patients. During prolactin suppression, mean oestrogen excretion rose significantly and the oestrogen provocation test became normal in all except 2 patients. Pregnancy occurred in all of the 15 patients desiring fertility. Abortion has occurred in 4 patients, all of whom are currently pregnant again. Nine pregnancies have reached term, with no complications from pituitary expansion. It appears that during hyperprolactinaemia there are defects in both positive and negative feedback of oestrogen on LH secretion, and that prolactin suppression in such patients is highly effective in restoring fertility.

Mechanism of induction of LH surge in the rhesus monkey: positive feedback of estrogen?

Mechanism of induction of LH surge in the rhesus monkey: positive feedback of estrogen?

Effects of Danazol on Pituitary Gonadotrophins in Post‐Menopausal Women

Multiple sampling was carried out in 4 postmenopausal women for measurement of LH and FSH before and at the end of a 1-week treatment period with Danazol (400 mg daily). A small but significant depression of FSH was found in 3 of 4 subjects, while a significant depression of LH was only seen in 1 subject. In view of the very modest gonadotrophin suppression demonstrated in these women it is possible that Danazol also exerts its profound and sometimes rapid effects through inhibition of positive oestrogen feedback and by direct actions on the ovaries and endometrium.

Undernutrition, puberty and the development of estrogen positive feedback in the female rat.

The development of the positive feedback of estrogen in normally fed animals and its possible alterations in animals subjected to restricted food intake was studied. Different doses of estradiol benzoate (EB), administered s.c. as a single injection to normal prepubertal rats of different ages, resulted in an increase in uterine weight which became more prominent as the animals approached puberty. Significant gonadotropin release was induced by EB only from Day 26 on. The LH response to EB measured in the afternoon (1600 h) of the second day following the injection increased with age; the older rats showing an elevation in LH levels after the administration of doses of EB which were ineffective in younger rats. In rats injected with the highest dose of EB (5 µg/100 g bw), gonadotropin release occurred 1 day earlier. Modification of the growth rate of rats by varying the milk supply during the nursing period, followed by normal postweaning feeding, revealed that attainment of a critical body weight is not essential for puberty to occur since animals reached puberty at the same age, but at different body weights. Other animals maintained after weaning under restricted diet did not reach puberty for as long as their access to food was restricted (Day 57). When food was made available ad libitum, vaginal opening and ovulation occurred within a week. At 42 days of age, the underfed rats had small uteri and restoration of food produced a dramatic increase in uterine weight and gonadotropin levels. At this age, the underfed rats responded to EB injection with a remarkable increase in gonadotropins which was even greater than that induced by a similar dose of EB in younger normally fed rats of similar body weight. Restoration of food followed by ES injection resulted in ovulation within 3 days. The results indicate that 1) the gonadotropin response to estrogen positive feedback develops gradually and quantitatively as the animal matures and 2) undernutrition-induced delayed puberty is not caused by inability of the hypothalamic-pituitary unit to respond to positive estrogen feedback, but rather to ovarian failure to release estrogen in amounts sufficient to trigger a gonadotropin surge. However, the fact that in underfed rats, basal gonadotropin levels were not elevated indicates that the steroid negative feedback was operative in these animals.

Stimulation of follicular growth with "pure" FSH in patients with anovulation and elevated LH levels.

Ovarian follicular growth was stimulated in 4 patients with clomiphene resistant polycystic ovary (PCO)-like disease, with "pure" human pituitary FSH during 10 cycles. In 8 cycles additional hCG was given to induce ovulation. Serum LH and FSH and plasma estradiol and progesterone were determined daily. From the response patterns of steroidogenesis, four functional stages of follicular development can be distinguished, each subsequent stage being characterized by an increasing spontaneous estradiol production and a decreasing capacity to produce extra estradiol in response to stimulation with additional hCG. It is concluded that the unpredictable response to gonadotropin stimulation of patients with PCO-like disease is due to the varying state of development of the follicles at the start of the stimulation. The suggestion is made, based on the different responses in 3 cycles of the same patient (EW), that the lack of positive estrogen feedback in patients with PCO-like disease may be a hyposensitivity to estrogens rather than an absolute insensitivity.

Regulation of LH Secretion in Aged Female Rats1

The regulation of luteinizing hormone (LH) secretion in aged female rats was investigated. No differences were seen in the responses to any of the treatments between aged rats which exhibited a constant estrous or a pseudopregnant-like state prior to ovariectomy. Following ovariectomy LH levels were significantly higher (p greater than .05) in the mature than in the aged rats. Treatment with estradiol benzoate (EB) reduced serum LH in both groups (p greater than .05). In mature ovariectomized-EB primed rats an LH-releasing dose of EB (25 mcg/100 g body weight) elevated LH levels at 24 and 26 hours following treatment when compared to pretreatment and oil-treated controls. This was not true in aged ovariectomized-EB primed rats. Gonadotropin releasing hormone induced an LH release in both mature and aged ovariectomized-EB primed rats. It is concluded that the cessation of reproductive cycles in the aged female rat appears to involve alterations within the positive estrogen feedback center of the anterior hypothalamus rather than in the pituitary or negative estrogen feedback center.

Effect of exposure to continuous light on estrogen-induced precocious sexual maturation in female rats.

Immature female rats, raised in either cyclic light (LD; 14 H LIGHT/10 H DARK) Or constant light (LL) were divided into 4 groups and given daily injections of estradiol benzoate (5, 10, or 25 ng) in 0.1 ml sesame oil starting at 24 days of age. Control animals received oil only. Injections were continued until vaginal opening (V.O.). Half of each group of animals was killed and dissected 1 day after V.O. Results indicate that both LL exposure and EB treatment accelerated sexual maturation (as indicated by the day of V.O.) with a significant interaction between the 2 treatments. Thre greatest difference in age at V.O. between LD and LL rats was observed at a dose of 10 ngEB/day. Body weights and uterine weights decreased with higher doses of EB, apparently reflecting the younger age at the time of V.O. No significant differences in ovarian weights were observed. Results are interpreted to indicate that increased exposure to light may change the sensitivity of the hypothalamic-pituitary axis to the positive feedback of estrogen.

A neuroendocrine predisposition for homosexuality in men

In male rats, androgen deficiency during a critical hypothalamic organizational period was shown to give rise to a predominantly female-differentiated brain, homosexual behavior, and demonstration of a positive estrogen feedback effect. A positive estrogen feedback effect was also induced in intact homosexual men in contrast to intact heterosexual and bisexual men. Thus in 21 homosexual men an intravenous injection of 20 mg Presomen (Premarin) produced a significant decrease of serum LH levels followed by an increase above initial LH values. In 20 heterosexual and in five bisexual men, by contrast, intravenous estrogen administration, while producing a significant decrease of the serum LH level, was not followed by an increase above the initial LH values. Using a radioimmunoassay, plasma testosterone levels and 24-hr urinary excretions of unconjugated testosterone of adult homosexual men were found to be in the normal range as observed in heterosexual men. This finding suggests that homosexual men possess a predominantly female-differentiated brain which may be activated to homosexual behavior by normal or approximately normal androgen levels in adulthood.

Reduction of estradiol-binding capacity of neural target tissues in light-sterilized rats.

Estradiol-binding capacity of the hypo-thalamus and parietal cortex, measured with tritiated estradiol, has been found to be significantly reduced in rats made anovulatory by exposure to continuous illumination when compared to controls of approximately equal weight maintained in a light-controlled (14 h light and 10 h dark) room. This finding suggests that constant light interferes with the normal replacement of estradiol-binding proteins in the brain. The decrease of the hypothalamic estrogen-receptors might account for the loss of the positive neurohormonal estrogen feedback inducing ovulatory LH release in the rat.

Role of estrogens in spontaneous ovulation: evidence for the positive feedback in hamsters.

Existence of the positive feedback of estrogen for release of ovulating hormone has been explored in cyclic hamsters by using antiestrogens. Oral administration of either ICI 46,474 (10 mg/kg) or clomiphene (20 mg/kg) at 17:00 hr on Day 3 (day of external vaginal discharge Day 1) of the cycle interfered with ovulation, vaginal discharge and mating behavior. Of the two isomers of clomiphene used only the isomer with known antiestrogenic properties (clomiphene B) blocked ovulation (10 mg/kg). Simultaneous administration of estradiol benzoate (.025 to 0.5 mg/kg, sc) but not of progesterone (4 mg/kg, sc) prevented the inhibitory effects of both antiestrogens and fully restored ovulation and external vaginal discharge. Intravenous injection of pituitary gonadotropins on Day 4 also restored ovulation to a varying degree but did not induce vaginal discharge in the treated hamsters. A similar administration of LH-RF (10 ME) proved ineffective. These results demonstrate the existence of the positive feedback of estrogen for the release of ovulating hormone in the hamster similar to that reported earlier in the 4-day cyclic rat. (Endocrinology90: 941, 1972)

The role of oestrogens in spontaneous ovulation: location of site of action of positive feedback of oestrogen by intracranial implantation of the anti-oestrogen I.C.I. 46474.

SUMMARY In an attempt to locate the site(s) of action of the positive feedback of oestrogen for ovulation, a potent anti-oestrogen, I.C.I. 46474, was stereotaxically implanted into various parts of the brain or into the anterior pituitary. A dose of 5 μg of the anti-oestrogen when implanted into the cerebral cortex or injected subcutaneously on the morning of the day before pro-oestrus in 4-day cyclic rats was only marginally active in interfering with ovulation. By contrast, when the same amount was implanted into the median eminence region or the anterior pituitary, ovulation failed to occur in 80–100% of the rats (P &lt; 0·05). Implantation of the cocoa butter vehicle alone into these regions interfered with ovulation in less than 35% of animals. Introduction of the anti-oestrogen into the anterior hypothalamic or mammillary region gave equivocal results. The data suggest that both the median eminence and the anterior pituitary contain receptors which can be blocked by the anti-oestrogen with resultant inhibition of ovulation. It is concluded that the positive feedback of oestrogen for ovulation is exerted both at the pituitary and the hypothalamic levels.

Role of Estrogens in Ovulation: A Study Using the Estrogen-Antagonist, I.C.I. 46,474

A possible role of estrogens in regulating ovulatory release of luteinizing hormone (LH) in the estrous cycle has been examined by using a potent estrogen antagonist— I.C.I. 46,474. When administered orally at 1700 hr or before on diestrus, butnot at 0945 hr on proestrus in 4-day cycling rats, the antiestrogen prevented ovulation from occurring on the morning of estrus. The antiestrogen was also effective in interfering with ovulation in hamsters and in immature rats and mice pretreated with PMS. The minimal effective dose for blocking ovulation in 100% of the adult rats was found to be 0.5 mg⁄kg. When ovulation was blocked by giving the antiestrogen at 1700 hr, it did not prevent vaginal cornification, mating behavior or uterine ballooning, but when inhibition was effected by administration earlier in the cycle, all these estrogen-dependent parameters were either blocked or modified. A significant drop in LH content from 23 to 12 μg /gland which was detected in association with ovulation on the day of estrus in the control animals was not found in the “blocked” rats (19 μg/gland). The inhibition of ovulation by the antiestrogen could be prevented either by an intravenous administration, just before the critical period on the day of proestrus, of LH (25 μg NIH-S-11/rat) or partially purified ovine hypothalamic extract, or by the mating stimulus. It could also be fully restored by the concurrent sc administration of estradiol benzoate (400 μ/grat). These results are interpreted to mean that the antiestrogen inhibits ovulatory surge of LH from the pituitary by interfering with the antecedent positive feedback of estrogen on the hypothalamus. It is concluded that the positive estrogen-feedback forms an integral part of the chain of events leading to the ovulatory surge of LH in the estrous cycle. (Endocrinology87: 542, 1970)

The role of oestrogens in spontaneous ovulation: evidence for positive oestrogen feedback in the 4-day oestrous cycle.

SUMMARY A possible involvement of oestrogens in regulating the ovulatory release of luteinizing hormone (LH) has been explored by using an oestrogenantagonist, clomiphene. When given orally in the afternoon on the day before pro-oestrus to rats with a 4-day cycle, the compound prevented ovulation on the morning of oestrus. This was not associated with interference with vaginal cornification, uterine ballooning or mating. Similarly, clomiphene prevented ovulation in hamsters when given at a corresponding stage of the cycle. In adult rats ovulation could be fully restored by the intravenous administration of LH or LH releasing factor at 14.00 hr. on the day of pro-oestrus. Oestradiol benzoate given simultaneously with clomiphene on the day before pro-oestrus or the stimulus provided by mating on the night of pro-oestrus were also effective in this respect. It is implicit in these findings that clomiphene interferes with ovulation by virtue of its anti-oestrogenicity. This indicates that a positive feedback of oestrogen is an integral part of the chain of events culminating in the ovulatory release of LH in the reproductive cycle.