The role of LH in the autofeedback inhibition of LH and FSH secretion in ovariectomized rats

This study examined the role of exogenous LH in the autofeedback regulation of LH and FSH release in ovariectomized rats. The rats were implanted with third ventricular cannulae three weeks after ovariectomy and fitted with silastic jugular cannulae one week later. Baseline hormone levels were established on the day of experimentation in conscious, unrestrained animals. Thereafter, experimental animals received intraventricularly (IVT) either a 9 ug or 20 ug dose of a purified preparation of human (h)LH that did not crossreact in our rLH RIA. In response to 20 ug, but not 9 ug of LH, plasma levels of both LH and FSH were significantly reduced during the following one hour period compared to values in controls receiving buffer IVT. Administration of ovine (o)LH (6 ug, IVT), a preparation which crossreacts in the rLH RIA, significantly elevated plasma levels of detectable LH during the experimental period indicating that LH reaches the blood stream from the third ventricle and, thus, may effect endogenous hormone release at either the pituitary or hypothalamic levels. However, in animals preinjected with 9 or 20 ug of hLH IVT one hour earlier the surge of both LH and FSH in response to LHRH (25 ng iv) was not different from that in the buffer-injected controls receiving LHRH which indicates that pituitary responsiveness was not suppressed by the effective dose of hLH. The results of this study suggest that the inhibitory shortloop feedback of LH on endogenous LH and FSH secretion in ovariectomized rats occurs at the level of the hypothalamus.     

Differential effects of castration on LH and FSH secretion in male and female rats.

Serum levels of LH and of FSH have been measured using specific radioimmunological procedures in normal controls and in male and female rats submitted to castration 1, 2, 7, 14, 21, 28 and 35 days before. Gonadectomy is followed by a rapid increase of serum levels of LH in males, and by a delayed response in females. The responses of serum FSH to castration are quantitatively and qualitatively similar in the two sexes. Both in males and in females an elevation of serum FSH levels is already present 1 day after the operation. Serum FSH continues to rise, between post-castration days 1 and 7 with a rather rapid slope, and at later intervals with a smoother progression.     

Plasma patterns of LH, FSH and prolactin in rats with a polycystic ovarian condition induced by oestradiol valerate

The patterns of plasma LH, FSH and prolactin concentrations were investigated in rats with a polycystic ovary condition (PCO). The condition was induced by treatment with oestradiol valerate 9 weeks before blood sampling. Serial blood samples were taken at 10-min intervals for 4 h from ten rats with PCO. All samples were assayed for LH, those from five animals for FSH and those from the remaining five animals for prolactin. In addition, five control animals with normal oestrous cycles were sampled during oestrus and the samples assayed for LH. Mean concentrations of LH, FSH and prolactin in rats with PCO were 140 ng/l, 76 micrograms/l and 7.6 micrograms/l respectively. All three hormones exhibited an episodic pattern. The mean peak amplitudes of LH, FSH and prolactin were 120 ng/l, 25 micrograms/l and 3.5 micrograms/l respectively. All three hormones exhibited a similar mean frequency of four or five episodes per 4 h. The LH and FSH patterns were closely synchronized; nearly all FSH peaks coincided with LH peaks. The prolactin pattern did not, however, correlate with that of the gonadotrophins. Despite the persistent oestrous condition of the animals with PCO, it was clear that their pattern of LH did not resemble that of cyclic animals in normal oestrus; in the normally cyclic animals in oestrus the pulse period was nearly twice as long and the pulse amplitude was more than sixfold greater than those in animals with PCO. We conclude that the unique episodic patterns of gonadotrophins are more important than mean blood concentrations of these hormones in establishing and maintaining the polycystic ovary syndrome.     

Effects of testosterone, FSH, and LH on oestradiol and progesterone secretion by preovulatory cumulus oophorus complexes of the rat.

Female Wistar rats exhibiting a regular 4-day oestrous cycle were included in this study. They were killed in succession on the day of pro-oestrus at 11.00, 18.00, and 22.00 h. From ovarian preovulatory follicles cumulus oophorus complexes (COCs) were isolated and subsequently cultured with or without testosterone (T), T plus FSH, or T plus LH. In control cultures COCs isolated at all investigated hours released similar amounts of oestradiol. T stimulated this basal secretion and the effect was usually enhanced in the presence of FSH or LH. In control cultures the amount of released progesterone was greatest when expanded COCs were isolated (22.00 h). T present in culture media diminished the amount of secreted progesterone. However, when T was added with FSH or LH a distinct stimulatory effect was observed, except in cultures with T plus FSH set up at 22.00 h. Previously, gonadotrophins alone did not effect progesterone secretion. The results suggest that T can regulate steroid, and especially progesterone secretion by COCs. Until the preovulatory gonadotrophin surge T can inhibit luteinization of COCs, while afterwards, acting synergestically with gonadotrphins (especially with LH), T can stimulate progesterone production in the cumulus granulosa cells.     

Stimulation of the Hypothalamus and FSH and LH secretion in the ferret

The acute effects of hypothalamic electrical stimulation on the secretion of FSH and LH have been examined in anestrous and estrous ferrets. Basal levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were higher in the anestrous than in the estrous animals; the anestrous animals showed a more marked increase in gonadotropin levels following hypothalamic stimulation than did the estrous animals whether the stimulation current was constant or increased in the course of the experiment. It is concluded that the physiological difference in the control of gonadotropin secretion in the estrous (vs the anestrous) ferret is not reflected in an increased sensitivity of the hypothalamo-hypophysial axis to stimulation.     

Antiprogesterone RU486 increases serum immunoreactive inhibin levels and LH:FSH and testosterone:oestradiol ratios in cyclic rats.

Since administration of the antiprogesterone RU486 to cyclic rats results in a dissociation of basal LH and FSH secretion we studied its effects on peripheral levels of inhibin, oestradiol and testosterone throughout the oestrous cycle. Cyclic rats were given RU486 (2 mg) twice daily (09.00 and 17.00 h) on metoestrus, dioestrus and pro-oestrus. Oil-treated rats were used as controls. Serum concentrations of immunoreactive inhibin in oil-treated rats increased from metoestrus to pro-oestrus and decreased at oestrus. RU486-treated rats had serum inhibin concentrations significantly increased over oil-treated rats at dioestrus and pro-oestrus, but not at oestrus. At both pro-oestrus and oestrus serum concentrations of LH, testosterone and oestradiol were significantly raised in RU486-treated rats compared with oil-treated controls. In contrast, serum FSH concentrations in RU486-treated rats were decreased on both days. Ovaries from RU486-treated rats showed an increased testosterone content at pro-oestrus, mainly in the interstitial tissue. The results of the present study demonstrate that RU486 has a stimulatory effect on inhibin secretion, and offer an explanation for the decrease in basal serum FSH levels. The low FSH secretion on the morning of oestrus in spite of the low levels of inhibin suggests that progesterone is involved in FSH secretion at this time.     

Inhibition of luteinizing hormone (LH)-releasing hormone-induced secretion of LH in rat anterior pituitary cell culture by testosterone without conversion to 5 alpha-dihydrotestosterone

The role of 5 alpha-reduction of testosterone in the inhibition of LH secretion was investigated in rat anterior pituitary cell cultures. Pituitary cells were preincubated with testosterone or dihydrotestosterone (17 beta-hydroxy-5 alpha-androstan-3-one) for 17 h and then with LHRH for an additional 4 h. Dihydrotestosterone was 6-fold more potent than testosterone in the inhibition of LHRH-induced LH release. Basal LH secretion was not affected by either androgen. The inhibition curves of testosterone and dihydrotestosterone were not shifted by the presence of the 5 alpha-reductase inhibitors 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one (4-MA) and 17 beta-N,N-diisopropylcarbamoyl-4-aza-androstan-3-one (DIPA). Neither 4-MA nor DIPA alone had an effect on either basal or LHRH-induced LH release. When pituitary cells were incubated with [3H]testosterone for 17 h, the radioactivities were found to be unmetabolized testosterone (66.9 +/- 2.4%), dihydrotestosterone (13.3 +/- 0.5%), androstenedione (15.9 +/- 1.3%), 5 alpha-androstane-3,17-dione (2.8 +/- 0.3%), and 3 alpha (beta), 17 beta-androstanediol (less than 1%). In the presence of 4-MA or DIPA, 5 alpha-reduction of testosterone was completely inhibited; androstenedione was the only metabolite. Androstenedione was only 12% as potent as testosterone in the inhibition of LHRH stimulation of LH release, and conversion of [3H]androstenedione to testosterone and dihydrotestosterone did occur in these cells. When [3H]dihydrotestosterone was incubated with pituitary cells, the radioactivities were dihydrotestosterone (64.4 +/- 0%), 5 alpha-androstanedione (19.3 +/- 1%), 3 alpha (beta), 17 beta-androstanediol (7.7 +/- 1.7%), and unknown polar metabolites. 4-MA and DIPA had no effect on the metabolism of dihydrotestosterone. These results indicate that both testosterone and dihydrotestosterone inhibit LHRH-induced LH release and that this activity of testosterone does not depend on its 5 alpha-reduction.     

Pituitary LH and FSH and testosterone secretion in infants with undescended testes.

Twelve male infants with undescended testes (5 bilaterally, 7 unilaterally) were studied between the ages of 1 week and 11 months. As in older pre-pubertal cryptorchid boys, a significant decrease of the LH response to LH-RH test was found, while basal plasma levels of gonadotrophins and FSH response to LH-RH were normal. Plasma testosterone levels were in the normal range, and Leydig cells responded to stimulation by HCG, the degree of this response being significantly and positively correlated to the LH peak elicited by LH-RH. It may be concluded that some early defect of the pituitary-Leydig cell axis is associated with undescended testis.     

Estriol affects prolactin and LH secretion in rats

The effects of estriol on serum prolactin (PRL) and LH levels, on the pituitary response to TRH and LHRH and on the synthesis and release of PRL from the anterior pituitary gland were investigated in female rats. The increase of serum PRL levels after estradiol administration was found to be associated with an increase of glutamic acid decarboxylase (GAD) and GABA-transaminase (GABA-T) in the hypothalamus. Thus, a study was carried out on the effects of estradiol and estriol on PRL secretion and on GAD, GABA-T and gamma-amino butyric acid (GABA) in the hypothalamus and the anterior pituitary. Under basal and TRH-stimulated conditions, estriol increased serum PRL levels, decreased basal serum LH levels, and increased the response to LHRH, in terms of LH release. Estradiol and estriol increased the synthesis and release of 3H-PRL from hemipituitary glands in incubations of pretreated animals. Both estrogens induced hyperprolactinemia, concomitantly with an increase of hypothalamic GAD and GABA-T activity. Estriol increased hypothalamic GABA concentration, but did not modify GABA concentration in the pituitary glands. Our results show that estriol, at relatively high doses, seems to be active in increasing PRL synthesis and release and in decreasing serum LH levels; it can also modify pituitary response to TRH and LHRH stimulation.     

Acute effects of oestradiol and progesterone on melittin- and gonadotrophin-releasing hormone-induced LH secretion.

It is well established that oestradiol and progesterone modulate gonadotrophin-releasing hormone (GnRH)-induced LH secretion from cultured rat pituitary cells. Short-term oestradiol and long-term progesterone treatment exert inhibition, while short-term progesterone and long-term oestradiol treatment lead to enhancement of GnRH-stimulated LH secretion. There are several lines of evidence to suggest that the steroid effects might be mediated via a mechanism involving modulation of the GnRH signal-transduction system. To evaluate the role of arachidonic acid, which serves as an intracellular signal transducer by itself or its lipoxygenase metabolites, in the mediation of oestradiol and progesterone actions, we examined their effects on melittin (activator of phospholipase (A2)-stimulated LH secretion. When pituitary cells from adult female rats were treated for 48 h with 1 nmol oestradiol/l or 1 nmol oestradiol/l plus 100 nmol progesterone/l, GnRH (1 nmol/l)-induced LH secretion was stimulated or inhibited respectively. However, melittin (10-300 nmol/l)-stimulated LH secretion remained unaffected after such treatment. Short-term treatment with oestradiol inhibited GnRH-induced LH secretion while progesterone treatment of oestradiol-primed cells led to a stimulatory effect. Interestingly, melittin-stimulated LH secretion was influenced in the same way after the short treatment paradigm. Perifusion studies were performed to assess the kinetics of these acute steroid actions further. Four separate perifusion chambers were continuously perifused with medium and stimulated for 2 min with 1 nmol GnRH/l or 1 mumol melittin/l every 50 min in a pulsatile fashion.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of inhibin and oestradiol in the control of FSH secretion in the sheep.

The relative importance of inhibin and oestradiol in the control of FSH and LH secretion in the ewe was investigated by passive immunization in intact animals and by hormone replacement therapy following acute ovariectomy, in the same experiment. Mature Scottish Blackface ewes on day 10 of the luteal phase were allocated to nine groups of four to five animals. Four groups were ovariectomized and immediately treated with either progesterone alone or in combination with steroid-stripped ovine follicular fluid ('inhibin') and/or oestradiol. Three further groups of ewes were left intact and injected with antibodies to the 1-26 alpha peptide fragment of porcine inhibin and/or oestradiol-17 beta. Two groups of animals were either ovariectomized alone with no further treatment, or were left intact and treated with normal sheep plasma to act as controls. Blood samples were collected at 2 h intervals from 12 h before until 48 h after ovariectomy/immunization, and from 12 to 24 h after treatment, blood samples were collected at 10-min intervals. After ovariectomy there was a large rise in the peripheral concentration of LH (P less than 0.001) which was not affected by treatment with progesterone alone but was completely prevented by treatment with progesterone and oestradiol. Treatment with inhibin had no effect on this post-castrational rise in LH. In intact ewes, immunization against oestradiol, alone or in combination with inhibin, resulted in a rise in the concentration of LH, while immunization against inhibin had no effect on LH concentration. The peripheral concentration of FSH showed a significant (P less than 0.001) increase after ovariectomy which was not affected by treatment with progesterone alone. Treatment with inhibin or oestradiol alone caused a significant (P less than 0.01) reduction in this rise, while treatment with inhibin and oestradiol together completely prevented this post-castrational rise in FSH concentration. Passive immunization against inhibin or oestradiol alone resulted in a transitory (P less than 0.01) rise in the peripheral concentration of FSH, while immunization against the two hormones in combination resulted in a significantly (P less than 0.01) larger rise. During the 14-h period after treatment, the rise in the concentration of FSH in this combined immunization group was not significantly different from that seen in the control ovariectomized group. These results provide evidence that FSH secretion is under the control of both oestradiol and inhibin, while reinforcing the hypothesis that inhibin is not involved in the regulation of LH production, which is under the dual control of oestradiol and progesterone.