Effects of progesterone (P) and antiprogestin RU486 on LH and FSH release by incubated pituitaries from rats treated with the SERM LY11701 8-HCl and/or recombinant human FSH

The aim of the present study was to investigate the role of the estrogen (ES) background on the effects of P or its antagonist RU486 on basal and LHRH-stimulated LH and FSH secretion. To do this, pituitaries collected from: intact rats in proestrus; rats injected with the ES antagonist LY11701 8-HCl; rats injected with recombinant-human FSH (r-hFSH) to stimulate ovarian hormonogenesis; and rats injected with both LY11701 8-HCl and r-hFSH were incubated with or without LHRH (10 nM) in the presence of P (100 nM) or RU486 (10 nM). RU486 decreased basal and LHRH-stimulated release of LH and FSH and LHRH self-priming in pituitaries from control rats, while P increased both pituitary responsiveness and LHRH self-priming. These effects were absent in pituitaries from rats treated either with the ES antagonist or r-hFSH, which, in the absence of P or RU486 in the incubation medium, reduced gonadotropin release. Because r-hFSH did not increase E2 serum concentration significantly, the putative FSH-dependent ovarian non-steroidal gonadotropin surge inhibiting factor (GnSIF) might be the hormonal cause of the reduced secretion of LH and FSH. Combined treatment with LY117018-HCl and r-hFSH had additive inhibitory effects on gonadotropin release. These results indicate that ES-inducible P receptor (PR) in the pituitary can be activated in a ligand-independent manner by intracellular messengers giving rise to enhanced basal and LHRH-stimulated gonadotropin secretion. The results also suggested that the r-hFSH-stimulated ovarian bioactive entity GnSIF and RU486 may share a similar mechanism of action involving pituitary PR.     

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.     

Patterns of LH and FSH release from perifused rat pituitaries in response to infusions of hypothalamic extract.

A continuous flow incubation (perufusion) system was developed in which the secretory responses of pools of hemipituitaries from adult male rats to hypothalamic extract (HE) were characterized by serial radioimmunoassay of LH and FSH in the effluent medium. There was in initial massive release of LH and FSH which, in the absence of HE, declined to low basal levels at a rate which depended on the flow rate. Thereafter, the baseline for LH continued to decline gradually while that for FSH was stable. The rate of LH and FSH release rose abruptly after addition of the HE to the medium and returned promptly to baseline after withdrawal of the HE. During continuous infusion of HE for five hours, LH secretion was maintained at a relatively constant, elevated level. The responses to repeated identical pulses of HE were highly reproducible. The variability between responses by any one pool of tissue was significantly less than between responses of separate pituitary pools including pools comprising right and left halves of the same glands. For any given pool of pituitaries of the relationships were linear between: 1) duration of HE pulses (concentration constant) and increases in LH output, and 2) log of concentration of HE (pulse duration constant) and increases inLH and in FSH output. Consistent responses were obtained for up to 12 hr, the maximum period tested.     

Effects of LHRH and long-acting LHRH on serum LH and FSH levels of healthy women

A comparison was made between the stimulatory effects of luteinizing hormone-releasing hormone (LHRH) and long acting luteinizing-releasing hormone (I.a. LHRH) on the gonadotropin secretion of normally menstruating women. The luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations were measured by RIA. The synthetic I.a. LHRH was found more potent than the parent hormone in terms of the magnitudes and durations of the LH and FSH responses. There was no close correlation between the initial gonadotropin values and the peak levels in normally menstruating women having basal LH and FSH values within the normal ranges.     

LHRH injected into the medial preoptic area potentiates LH secretion in ovariectomized estrogen-primed and proestrous rats

To determine if luteinizing hormone releasing hormone (LHRH) might act within the central nervous system to modulate its own secretion, microinjection of LHRH into the medial preoptic area (MPO) was performed at 13:00 h in both the ovariectomized estrogen-primed and proestrous rat, and the effects on the afternoon rise in the serum concentration of luteinizing hormone (LH) were studied. Microinjection of 5 ng LHRH into the MPO in the ovariectomized estrogen-primed rat resulted in a significant increase in serum LH from 16:00 to 19:00 h compared to the value in the saline-injected rat, whereas the injection at a dose of 2 ng did not induce a significant change. The injection of 5 ng LHRH into the third ventricle in the ovariectomized estrogen-primed rat induced a transient increase in serum LH immediately after the injection, followed by recovery to the preinjection concentration by 1 h, indicating that the potentiating effect of 5 ng LHRH in the MPO was not due to the LHRH leaked into the third ventricle. Finally, microinjection of 5 ng LHRH in the proestrous rat induced an early increase in serum LH, resulting in an advancement of the peak of the afternoon rise by 1 h. It is suggested that LHRH secreted in the MPO may, directly or indirectly, stimulate its own secretion in the median eminence to produce the surge of LH secretion.     

Failure of metoclopramide to influence LH, FSH and TSH secretion or their responses to releasing hormones.

Intravenous metoclopramide (MET) (10 mg) induced a brisk PRL response with a mean +/- SEM peak of 85.3 +/- 7.7 ng/ml maximal at 30 min. L-Dopa, but not atropine pre-treatment, attenuated the prolactin (PRL) response to MET. This indicates that the antidopaminergic properties of MET mediate PRL secretion. MET did not influence basal levels of TSH, LH or FSH. Neither did it affect their response to the respective releasing of hormones. Our results indicate that dopaminergic blockade induced by iv MET, does not influence the secretion of the pituitary glycoprotein hormones.     

LH and FSH responses to luteinizing-releasing hormone in normal,adult, human males

Time-response and dose-response relationships were established for the LH and FSH response to single intravenous bolus injections of synthetic LRH. Sixteen normal adult human males, ages 19–45 were studied, and 80 individual tests were performed using a broad range of LRH doses from 0–3000 μg. Serum gonadotropins were measured at frequent intervals ranging from ?30 to 180 min after LRH injection. The curves describing changes in blood LH and FSH with time were not superimposable at any dose level. The 50% decay time for the LH response showed a significant linear log-dose relationship to LRH.For LH, dose-response relationships existed for both, the peak LH release, and the total LH secretion (area under the time-response curve). No minimal or maximal effective doses were reached for LH within the dose range from 1 to 3000 μg LRH. The smallest dose (measured as peak LH concentration), that produced a response significantly different from saline injections, was 1.58 μg/subject; judged by total LH secretion (area under the time-response curve) the smallest dose producing a significant response was 2.39 μg/subject. No dose-response relationship existed for the peak FSH release. Judged by total FSH secretion (area under the time-response curve), the effects of LRH were dose related; the smallest effective dose was 20 μg LRH. As for LH, no maximal effective dose was reached within the dose range studied.The 95% confidence intervals for the peak responses to an intravenous bolus injection of 100 μg synthetic LRH were 400%–800% of the individual mean base line LH concentration, and 100%–200% of the individual mean base line FSH concentration. Serum testosterone did not change significantly in response to single bolus injections of LRH at any of the dose levels studied. The peak LH responses to any dose of LRH were positively correlated to the individual mean base line LH concentrations. No correlations were observed between the peak LH or FSH responses and age, race, marital status, body weight, or body surface area of the subjects.In a second series of studies, a 2-hr, constant infusion of synthetic LRH was administered at five different infusion rates (doses) to four normal adult human males for a total of 20 infusions. Serum LH and FSH responses were sustained at dose related levels characteristic of each individual during the entire LRH infusion period. In contrast to the lack of testosterone responses to bolus injections of LRH, serum testosterone rose significantly in response to all dose levels of LRH infusion. These are the most extensive pharmacologic studies of LRH-LH and LRH-FSH relations in man yet reported.     

Content of LH, FSH, and growth hormone in the pituitaries of pregnant and anestrous sheep.

The total content of LH, FSH, and growth hormone was measured in pituitaries from anestrous ewes and from ewes at known stages of pregnancy. LH content was lower in the pregnant ewes than in the anestrous group. Compared with the anestrous group, a significant drop in mean LH content was seen by days 40-50 of pregnancy (894 vs 350 mug, P less than 0.001), and it reached its lowest value by 120-135 days of pregnancy (43 mug, P less than 0.001). In sheep 148 days of pregnant, mean LH content was higher than in the latter group (155 mug). The correlation coefficient between the stage of gestation and the LH content was 0.63 (P less than 0.01). There was no significant change in mean FSH content in ewes up to 135 days pregnant (range 1196-1550 mug) compared with anestrous ewes (1023 mug). In the group 148 days pregnant (531 mug), a significant decrease was seen compared with ewes at other stages of pregnancy (P less than 0.05). Stage of gestation and FSH content were poorly correlated (r = 0.07). No significant differences in growth hormone content were seen in any of the groups. The results suggest that the progressive reduction in LH response to synthetic GnRH which has been reported for pregnant sheep may be due to selective inhibition of LH biosynthesis.     

FSH and LH responses to GnRH after ovariectomy in postmenopausal women

OBJECTIVE: Whether the postmenopausal ovary is still playing a role in the control of gonadotrophin secretion in response to GnRH has not been investigated. The aim of the present study was to test this hypothesis by examining changes in basal and GnRH-induced gonadotrophin secretion in postmenopausal women after bilateral ovariectomy. DESIGN: The responses of LH and FSH to GnRH [10 microg intravenously (i.v.)] were investigated in postmenopausal women from 2 days before to 8 days after total abdominal hysterectomy plus bilateral ovariectomy. PATIENTS: Nine postmenopausal women aged 52-67 years and between 5 and 15 years after menopause. In all cases the ovaries were histologically normal. MEASUREMENTS: Pituitary responses to GnRH were calculated every 12-24 h as the net increases in LH (DeltaLH) and FSH (DeltaFSH) at 30 min above the basal values. Basal values of oestradiol (E2) and testosterone were also measured. RESULTS: Basal values of FSH showed a significant decrease on postoperative days 2 (P < 0.01) and 8 (P = 0.03) as compared to day 0, while at the same time points after the operation LH values were marginally lower than on day 2 (P = 0.05). Serum E2 values showed a gradual increase up to postoperative day 1 (P = 0.04) and a gradual decline thereafter. Basal testosterone concentrations decreased gradually and significantly after ovariectomy and were significantly lower on day 8 than on day 0 (P < 0.01). DeltaFSH and DeltaLH responses to GnRH did not change significantly with time. A temporary increase at 12 h after the operation was not significant. CONCLUSIONS: These results demonstrate for the first time that the removal of the ovaries in postmenopausal women does not affect GnRH-induced gonadotrophin secretion in the short term. It is suggested that the postmenopausal ovary is not a dominant regulator of hypothalamic-pituitary interactions.     

Endogenous excitatory amino acid regulation of the progesterone-induced LH and FSH surge in estrogen-primed ovariectomized rats.

The role of endogenous excitatory amino acid neurotransmission in the regulation of progesterone and triamcinolone acetonide-induced LH and FSH release was examined. Estrogen-primed ovariectomized rats were utilized in this study. Progesterone or triamcinolone acetonide (1 mg/kg body weight) treatment led to a highly significant elevation of serum LH and FSH levels 5 h later. Treatment with the selective noncompetitive NMDA receptor antagonist, MK801, had no effect on serum LH and FSH levels when compared to estrogen controls. However, MK801 administered 1 h prior to progesterone or triamcinolone acetonide administration completely blocked their ability to induce LH and FSH surges. These studies demonstrate for the first time the involvement of endogenous excitatory amino acid neurotransmission in the mediation of progesterone and corticosteroid-induced LH and FSH surges.     

Inhibitory effect of central LHRH on LH secretion in the ovariectomized ewe

The role of central luteinizing hormone releasing hormone (LHRH) in the control of pulsatile LHRH and luteinizing hormone (LH) secretion was investigated in ovariectomized adult ewes. Injection of LHRH (2.1-21 pmol) into the third cerebral ventricle caused a delayed but sustained inhibition of LH secretion. Pulse frequency, pulse amplitude and mean LH levels were reduced significantly when compared with the responses to the control injection of saline (50 microliters). The inhibitory effect of centrally administered LHRH was not accompanied by a reduction in the pituitary responsiveness to intravenous LHRH. In contrast to the effect on LH, plasma levels of follicle-stimulating hormone (FSH) and prolactin were unaffected by central LHRH. The inhibitory action of LHRH was antagonized by prior injection of an LHRH antagonist ([N-Ac-D-Nal(2)1, D-p-Cl-Phe2, D-Trp3, D-hArg (Et2)6, D-Ala10] LHRH, 69 pmol) into the third ventricle. Central injection of the LHRH antagonist alone (at the same concentration) did not influence any characteristic of pulsatile LH secretion. In conclusion, these data indicate that exogenous administration of LHRH into the brain exerts a dose-related and receptor-mediated inhibition of LHRH pulse generator activity. However, the physiological significance of endogenous LHRH in the regulation of the LHRH pulse generator remains unresolved.     

Prostaglandin-stimulated LH release in cyclic and ovariectomized rats

The ability of prostaglandin (PG) E2 treatment to stimulate luteinizing hormone (LH) release was compared in cyclic (4-day) and ovariectomized rats. PGE2 (500 micrograms) was injected sc and plasma LH concentration was determined in serial jugular blood samples. Administration of PGE2 at 13.30 h on each day of the oestrous cycle resulted in a significantly greater increase in plasma LH levels at pro-oestrus and oestrus than at dioestrus 1 and 2. This differential response by the hypothalamo-hypophyseal axis during the oestrous cycle implicates regulatory activity by ovarian steroid feedback. In oestrogen-primed ovariectomized rats, PGE2 administration stimulated a significant increase in plasma LH, but similar treatment in non-primed castrates decreased plasma LH levels. This finding suggests a major role for oestrogen in regulating this response.     

Acute desensitization of pituitary FSH response to LHRH in ovariectomized rats: further evidence that in the presence of ovarian proteins the LHRH-dependent, LH-like component of FSH release becomes apparent

Pulsatile release of LHRH and short-term pituitary desensitization to LHRH in the rat are believed to be necessary for the maintenance of LH pulsatility. In contrast, FSH release is partly induced by LHRH release and is partly LHRH-independent. This LHRH-independent release of FSH is subject to inhibitory feedback control by ovarian proteins (probably inhibin), and may obscure an LHRH-induced short-term loss of pituitary FSH responsiveness to LHRH. The object of this study was to establish whether short-term pituitary desensitization to single doses of LHRH results not only in a loss of LH response, but also of FSH response. Ovariectomized rats were used to eliminate the influence of steroid feedback. A group of ovariectomized rats was pretreated with steroid-free bovine follicular fluid (bFF) to suppress LHRH-independent FSH release, and phenobarbital to suppress LHRH-dependent FSH release respectively, 7 and 1 h before administration of LHRH. Another group received phenobarbital only. The animals were injected sequentially with either low or high doses of LHRH (1.25 or 10 ng/100 g body weight at times 0 and at 80, 120 or 180 min, and 6.25 or 50 ng/100 g at 60 min). Blood was taken for FSH measurements before and 5 and 10 min after each injection. Rats pretreated with bFF and phenobarbital showed an acute FSH response related to the dose of injected LHRH. No dose-response curve was seen in animals which had only been pretreated with phenobarbital.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pulsatile GnRH treatment of the ovariectomized rat and release of LH and FSH

The effect of pulsatile GnRH administration on the levels of LH and FSH was investigated in rats that had been ovariectomized 2 weeks earlier. Also the asynchronous occurrence of endogenous and GnRH-induced LH and FSH pulses was analysed. A small pulse dose of GnRH (1.25 ng/100 g) was given iv at a frequency of once every 60 min or once every 120 min during 24 h. A larger dose of 5 ng/100 g was given once every 60 or 120 min during either 24 h or 96 h. Blood was sampled arterially every 5 min around the two first and last GnRH injections and LH and FSH were measured. Only the treatment with the larger GnRH pulse dose resulted in a change of LH and FSH plasma levels. LH levels declined under all circumstances, whereas FSH was found to be increased temporarily after 24 h of treatment. The pituitary LH response to pulses of GnRH (5 ng/100 g) decreased irrespective of the frequency or duration with which GnRH was administered. There was a marked asynchronicity between LH and FSH pulses and almost every injection of GnRH (5 ng/100 g) resulted in clear LH pulses but not in FSH pulses.