Self-priming effect of LH-RH on pituitary gonadotropins in hyperprolactinemic women

To investigate how various concentrations of serum prolactin (PRL) influence the priming effect of luteinizing hormone releasing hormone (LH-RH) on the pituitary gland, 24 women with various blood PRL concentrations received intravenous injections of 100 micrograms of synthetic LH-RH twice at an interval of 60 minutes and their serum LH and follicle-stimulating hormone (FSH) were measured and analysed. In the follicular phase with a normal PRL concentration (PRL less than 20 ng/ml, n = 6), marked first peaks of the two hormones following the first LH-RH stimulation and enhanced second peaks after the second LH-RH administration were observed, indicating a typical priming effect of LH-RH on gonadotropins, though the second response of FSH was more moderate than that of LH. In hyperprolactinemia, in which the serum PRL concentration was higher than 70 ng/ml (n = 13), the basal concentration of gonadotropins was not significantly changed but the priming effect of LH-RH on LH and FSH was significantly decreased (p less than 0.01). No marked second peaks of LH and FSH were observed, suggesting an inhibitory effect of hyperprolactinemia on the second release of LH and FSH. In contrast, this effect was restored in a group of women whose serum PRL concentration was between 30 and 50 ng/ml (n = 5). Furthermore, enhanced second peaks of both LH and FSH were noted after successful bromocriptine therapy reduced hyperprolactinemia (PRL greater than 70 ng/ml) to less than 25 ng/ml (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibitory control of the pituitary LH secretion by LH-RH in male rats.

Luteinizing hormone-releasing hormone (LH-RH) was administered to prepubertal male rats (intact, castrate or castrate-adrenalectomized, 60 g body weight) for 28 days (1 microgram LH-RH/day, s.c.), at a 10-fold physiological dose, as compared to the minimal FSH-releasing dose of 100 ng/rat s.c. In intact rats, serum LH and weight of androgen-dependent organs (vented prostate, seminal vesicles) were reduced after 14 days of treatment. In castrate rats, the postcastration rise in serum LH was abolished by treatment. Pituitary LH content, FSH secretion and prolactin secretion were not suppressed. Hypothalamic LH-RH was increased at 14 and 21 days. In castrate adrenalectomized male rats, LH secretion was also suppressed by 1 microgram LH-RH s.c. x 28 days. The hypothalamic LH-RH content did not increase. The pituitary LH-RH receptor level was not down-regulated after 14 days treatment either in intact or castrate male rats. Pituitary inhibition (LH release) in rats by a supraphysiological dose of LH-RH given for 28 days indicates that the optimal regime for chronic treatment has to be determined by monitoring LH release at regular intervals. Direct pituitary inhibition by LH-RH may explain some of the unexpected antifertility effects observed with high doses of LH-RH.     

Serum luteinizing hormone and ovulatory response to luteinizing hormone-releasing hormone in the estrous and anestrous domestic cat.

A heterologous double antibody radioimmunoassay was developed to measure changes in serum luteinizing hormone (LH) concentrations in estrous and anestrous queens (female domestic cats), following a single injection of varying doses (0--25 microgram) of luteinizing hormone-releasing hormone (LH-RH). No increase in serum LH was detected in any of the estrous or anestrous queens following a single saline injection. Treatment with LH-RH resulted in a sharp increase in serum LH concentration in both estrous and anestrous queens. Ovulations as observed by the presence of corpora lutea at laparoscopy occurred in none of four, one of four, two of four and four of four estrous queens receiving 0, 5, 10 or 25 microgram of LH-RH, respectively. Mean serum LH concentration of the ovulating queens was maintained at a higher level and did not return to basal level at the same time as that of nonovulating queens. The data show that: LH-RH can cause release of LH in both estrous and anestrous queens and induce ovulation in the estrous cat; the magnitude of LH response is influenced by the stage of the reproductive cycle; and the duration during which LH is maintained above basal level may play a significant role in ovulation induction in this coitus-induced ovulatory species.     

Mechanism of the postcoital contraceptive effect of LH-RH in the rat. I. Serum hormone levels during chronic LH-RH Administration.

The mechanism of the postcoital contraceptive effect of luteinizing hormone-releasing hormone (LH-RH) was studied in the rat. 200 mcg of LH-RH administered daily over Days 1-7 of pregnancy produced a dramatic inhibition of pregnancy. This inhibition was directly correlated with induced 'surges' in serum LH over Days 1-4. Serum follicle stimulating hormone and prolactin were, in general, reduced over this same time period. A 48-hour delay in the preimplantation (Day 3) 'surge' in serum estradiol accompanied by a significant (ps less than .05 and less than .01) reduction in serum progesterone on Days 3, 4, 6, and 7 was also observed. The delayed 'surge' in serum estradiol on Day 5 and reduction in serum progesterone was correlated with an increase in folliculogenesis and luteolysis of established corpora lutea, respectively. These data suggest that in the rat LH-RH induces a rise in serum LH which is luteolytic during pregnancy and delays the serum estradiol surge necessary for normal implantation.     

Cyclosporine A inhibits the secretion of certain anterior pituitary hormones in patients with nephrotic syndrome.

To clarify the effects of cyclosporine A (CsA) on the secretion of serum thyrotropin (TSH), prolactin (PRL), luteinizing hormone (LH) and follicular stimulating hormone (FSH), we performed TRH and LH-RH testing in 4 patients with the nephrotic syndrome before and after the administration of CsA, 6 mg/kg/day for 4 to 12 weeks. Prior to CsA all patients responded normally to TRH with respect to TSH and PRL secretion. Two patients showed normal response of LH and FSH to LH-RH stimulation while the response in 2 other patients, who were both menopausal, was exaggerated. By the third or fourth week of CsA administration the basal and peak TSH and PRL values declined significantly in all patients in response to TRH stimulation while those of LH and FSH showed only a modest decrease in response to LH-RH stimulation. Two to 4 weeks after the cessation of CsA the response of TSH, PRL and FSH returned to the pretreatment level. These observations suggest that: 1) CsA exerts an inhibitory effect on the secretion of at least TSH and PRL in humans, and 2) the effect of CsA on the pituitary may be partially reversible after the cessation of the therapy.     

Basal and LH-RH-stimulated gonadotropin release after transport stress in male rats

A total of 120 male rats of the Sprague-Dawley-strain (6 weeks old) were used in this experiment. 5 groups of 12 animals each were treated intraperitoneally with 200 ng gonadotropin releasing hormone (LH-RH) per animal. 30 minutes later blood was sampled by heart puncture. Group I were animals without transport, group II immediately after, group III one day, group IV one week and group V six weeks after a standardised transport. Another 5 groups were subjected to the same protocol but received saline i.p. instead of LH-RH. Serum levels of LH and FSH were estimated by radioimmunoassay. LH and FSH serum levels could be stimulated by LH-RH in all groups. A significant rise of basal and LH-RH stimulated LH levels was observed until the first day after transport. Thereafter a drop was registered. No consistent patterns of basal as well LH-RH stimulated FSH-levels were noted. These data combine to suggest an elevation of LH-RH secretion as response to the stress. This results in a sensibilisation of the pituitary to exogenous LH-RH.     

Accuracy of serum luteinizing hormone and serum testosterone measurements to assess the efficacy of medical castration in prostate cancer patients

Background

Luteinizing hormone-releasing hormone (LH-RH) agonists are the standard for androgen deprivation therapy (ADT) in prostate cancer (PCa) patients. Current guidelines recommend serum testosterone measurement to assess the efficacy of ADT and to define castration resistance. However, serum testosterone does not reflect the exclusive effect of castration due to its extratesticular production. The aim of this study is to analyze if serum LH reflects better than serum testosterone the activity of LH-RH agonists.

Methods

Serum LH and serum testosterone were measured with chemiluminescent immunoassay (CLIA) in a cohort study of 1091 participants: 488 PCa patients “on LH-RH agonists”, 303 “off LH-RH agonist” in whom LH-RH agonists were withdrawn, and 350 men with PCa suspicion “no LH-RH agonist” who never received LH-RH agonists. In a validation cohort of 147 PCa patients, 124 on “LH-RH agonists” and 19 “off LH-RH agonists”, serum testosterone was also measured with liquid chromatography and tandem mass spectrometry (LC MSMS).

Results

The area under the curve (AUC) to distinguish patients “on versus off LH-RH agonists” was 0.997 for serum LH and 0.740 for serum testosterone, P < 0.001. The 97.5 percentile of serum LH in patients “on LH-RH agonists” was 0.97 U/L, been the most efficient threshold 1.1 U/L. The AUCs for serum LH, testosterone measured with CLIA and with LC MSMS, in the validation cohort, were respectively 1.000, 0.646 and 0.814, P < 0.001. The efficacy to distinguish patients “on versus off LH-RH agonists” was 98.6%, 78.3%, and 89.5% respectively, using 1.1 U/L as threshold for serum LH and 50 ng/dL for serum testosterone regardless the method.

Conclusions

Serum LH is more accurate than serum testosterone regardless the method, to distinguish patients “on versus off LH-RH agonists”. The castrate level of serum LH is 1.1 U/l. These findings suggest that assessment of LH-RH agonist efficacy and castration resistance definition should be reviewed.

     

A paradoxical castration effect on LH-RH levels in male rat hypothalamus and serum

Serum and hypothalamic luteinizing hormone releasing hormone (LH-RH) was lowered in young mature male rats after castration. Testosterone injections raised the hypothalamic LH-RH content significantly. The mean value of serum LH level was elevated by testosterone, but not significantly. Hypothalamic LH-RH content was also lowered by hypophysectomy. In this circumstance, testosterone injections significantly increased LH-RH content. These results suggest that there may be a positive feedback of testosterone upon the hypothalamic LH-RH release and synthesis mechanisms.     

The role of protein kinase C in LH release

To investigate the postreceptor mechanism, especially the role of protein kinase C (C-kinase), in luteinizing hormone (LH) release from anterior pituitary cells, dispersed rat anterior pituitary cells were stimulated with luteinizing hormone-releasing hormone (LH-RH), [D-Ser(tBu)]6 des-Gly-NH2(10) ethylamide (Buserelin), 12-0-tetradecanoyl phorbol-13-acetate (TPA) and trifluoperazine (TFP) and the LH released into the medium was determined by radioimmunoassay. LH released by combined stimulation with TPA and either LH-RH or Buserelin was significantly less than that released by LH-RH or Buserelin alone (LH-RH: p less than 0.05; Buserelin: p less than 0.01). It is thought that this paradoxical phenomenon occurred due to desensitization accompanied by down-regulation of LH-RH receptors induced by TPA. This hypothesis was supported by the finding indicating that the binding capacity of LH-RH receptors decreased in a time-course manner during incubation with TPA. The amount of LH released by combined stimulation with TPA and TFP was significantly greater than with TPA alone (P less than 0.01). This suggests that TFP has dual actions, i.e., facilitating and inhibiting LH release.     

Gonadotrophin-releasing hormone treatment for induction of follicular maturation and ovulation in amenorrhoeic women with anorexia nervosa.

Follicular maturation and ovulation can be induced in amenorrhoeic women with anorexia nervosa by long-term treatment with 500 mug of luteinizing hormone releasing hormone (LH-RH) every eight hours. In some women, however, treatment with LH-RH alone results in ovulatory menstrual cycles with indications of luteal phase insufficiency. Human chorionic gonadotrophin (HCG) was therefore given with LH-RH during three treatment cycles. This resulted in ovulation and normal corpus-luteum function, as shown by the occurrence of a single pregnancy in the only involuntarily sterile patient. During the prolonged LH-RH treatment the LH response to LH-RH increased in parallel with the increased oestrogen secretion while the follicle-stimulating hormone response to LH-RH decreased. These changes in the pituitary responsiveness to LH-RH may result from modulating effects on the pituitary by the sex steroids.     

Ultrastructural observations of granule extrusion from rat anterior pituitary cells after injection of LH-releasing hormone

Summary In order to observe the ultrastructural aspects of granule extrusion from gonadotrophs, the authors injected pure, natural porcine LH-releasing hormone (LH-RH) into persistent-estrous (PE) rats. Clear-cut extrusions of secretory granules appeared from LH-gonadotrophs 2.5, 5 and 15 minutes after the injection. Massive extrusion was observed at 15 minutes. Serum LH and FSH were also estimated by radioimmunoassay on blood samples taken at the same times after the injections. LH was increased in the blood sera after the injection of LH-RH, but serum FSH was not significantly different among the various treated rats. The rise in serum LH after LH-RH injection was well correlated with the ultrastructural phenomenon of granule extrusion from LH-gonadotrophs.The study was supported by USPHS Grants AM 12583, AM 09094 and AM 07467.The authors acknowledge the able assistance of Mrs. Martha Castilleja in San Antonio and of Meredith M. Nickel in New Orleans.     

Role of luteinizing hormone-releasing factor (LH-RF) and LH on maintenance of early gestation in rats.

The role of luteinizing hormone (LH) and LH-releasing hormone (LH-RH) in the maintenance of early pregnancy in rats was studied. Serum levels of progesterone (P) and LH were measured daily in untreated pregnant rats from Day 4 through parturition. Serum levels of P and LH were determined on Days 11 and 15 of pregnancy in animals treated with antisera to LH (LH-A/S) and to LH-RH (LH-RH-A/S) on Days 8-10. Serum levels of P peaked on Days 7 and 16 in untreated animals, after which they declined sharply just before delivery. Serum LH fluctuated between 30-160 ng/ml during pregnancy but did not exhibit any distinctive peaks. Treatment with .2 ml LH-A/S on Days 8-10 reduced serum P to virtually undetectable levels on Day 11, and only a slight recovery was evident on Day 15. Lower doses of LH-A/S had no effect. Administration of 1.3 ml LH-RH-A/S had no effect on serum levels of P or LH, and did not impede fetal development. The results indicate that LH is essential to the luteotropic complex of early pregnancy in the rat, and also that LH-RH-A/S can maintain to some extent basal levels of P and LH during early pregnancy.     

An increase of pituitary 3', 5' cyclic adenosine monophosphate produced by estradiol benzoate in vitro: possible implication of this increase in the secretion of luteinizing hormone.

In an attempt to study the site and mechanism of action of estrogen in producing positive feedback control, porcine anterior pituitary slices were incubated in vitro in the presence of estradiol benzoate (EB). EB elevated pituitary cyclic AMP concentration within 5 min and augmented pituitary release of luteinizing hormone (LH). The magnitude of increase of cyclic AMP and LH release was related to the doses of EB used. Also, luteinizing hormone releasing hormone (LH-RH) elevated pituitary cyclic AMP concentration and stimulated pituitary release of LH. The magnitude of increase of cyclic AMP and LH release was inversely related to the doses of LH-RH used. EB and LH-RH were additive in increasing cyclic AMP. Progesterone and clomiphene citrate interfered with an increase of pituitary cyclic AMP produced by EB, but did not significantly affect the basal level of pituitary cyclic AMP. Testosterone propionate, human chorionic gonadotropin and hexestrol were without effect on either basal or stimulated level of pituitary cyclic AMP. Since cyclic AMP and dibutyryl cyclic AMP (DBC) stimulated LH release, it is suggested that EB directly stimulates the release of LH by augmenting cyclic AMP synthesis in the anterior pituitary.     

Suppression of gonadotropin secretion and prevention of ovulation in the rat by antiserum to synthetic gonadotropin-releasing hormone

Administration of an antiserum (0.10–0.25 ml/rat) to the synthetic decapeptide “luteinizing hormone releasing hormone” (LH-RH) suppressed the cyclic surge of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in proestrous rats and prevented ovulation; exogenous LH reversed the block of ovulation. Serum prolactin levels remained unaffected. In ovariectomized rats, the antiserum suppressed the elevated serum levels of both gonadotropins. These findings are compatible with the view that the synthetic decapeptide is identical with the natural hypothalamic hormone that regulates the secretion of both LH and FSH.     

Effect of pre-incubation with different concentrations of LH-RH on subsequent LH release caused by supramaximally active amounts of LH-RH; role of LH-RH-induced protein synthesis.

Anterior pituitary glands from intact diestrous female rats were incubated for two consecutive periods of 3 hours. During the first period various submaximally active amounts of luteinizing hormone-releasing hormone (LH-RH) were added to the media, whereas during the second period a supramaximally active concentration of LH-RH was present. When during the second incubation period protein synthesis was inhibited by cycloheximide, the amount of luteinizing hormone (LH) released during that period was positively correlated to the concentration of LH present during the first incubation period. This relationship was not seen when cycloheximide was absent, or when cycloheximide was present throughout both periods. Total LH was not affected by LH-RH; thus no effect of LH-RH on LH synthesis was observed. It is concluded that the amounts of protein synthesized by the pituitary glands in response to the different amounts of LH-RH during the first incubation period can constitute a limiting factor for the response to the supramaximally active amount of LH-RH added during the second incubation period.     

Comparison of mammalian luteinizing hormone releasing hormone (LH-RH), and of an analog (ICI 118630), on luteinizing hormone and ovarian steroid (progesterone, oestradiol) secretions in laying hens. (Gallus domesticus)

This experiment was conducted to compare the luteinizing hormone (LH), progesterone (P4) and oestradiol (E2) release in response to injections of various doses of synthetic mammalian luteinizing hormone-releasing hormone (LH-RH) and of an LH-RH agonist, ICI 118630, administered to laying hens 4 to 9 hours after a mid-sequence ovulation. Plasma LH increased significantly within 10 minutes of injection of either compound whereas any increases in plasma steroid concentrations were discerned later, at approximately minutes post-injection. No dose-response relationship was found for either compound with respect to LH release, but ICI 118630 appeared more potent than LH-RH. This analog also produced a greater mean incremental rise in plasma progesterone, but not oestradiol, than LH-RH, and this was found in animals injected at a time when the largest ovarian follicle was not mature. These result suggest that ICI 118630 is a more potent releasing hormone in the hen at the level of the pituitary, and that it may have a stimulating effect on ovarian progesterone secretion.     

Mechanism of LH release in cultured rat pituitary cells

To investigate the mechanisms of the synthesis and the release of gonadotropin, rat anterior pituitary cells were stimulated in vitro with luteinizing hormone releasing hormone (LH-RH), [D-Ser(tBu)]6 des-Gly-NH2(10) ethylamide (Buserelin) and 12-0-tetradecanoyl phorbol-13-acetate (TPA), and then the LH and LH-beta subunit released into the medium were determined by radioimmunoassay. Buserelin showed its biological activity at a much lower concentration than LH-RH, but both of them caused the release of LH and LH-beta subunit in a dose-dependent manner. Furthermore, intracellular LH synthesis from LH-beta subunit by stimulation with LH-RH or Buserelin was also found. After inducing various degrees of desensitization by stimulation with LH-RH or Buserelin in a dose-dependent manner (the first stimulation), pituitary cells were stimulated with a fixed dose of TPA (the second stimulation) and the released LH was assayed. LH was released almost constantly by the second stimulation, regardless of the dose used for the first stimulation. These results suggest that the C-kinase pathway was unaffected by the desensitization induced with LH-RH or Buserelin.     

The effects of gonadectomy and oestradiol-17 beta on pituitary responsiveness to LH-RH in the adult male marmoset (Callithrix jacchus).

Exogenous luteinizing hormone-releasing hormone (LH-RH) administered in a wide range of doses (0.2-25 micrograms) to intact male marmoset monkeys induced a marked increased in plasma luteinizing hormone (LH) concentrations. Maximum LH concentrations achieved after injection of LH-RH occurred progressively later as the dosage increased. Bilateral orchidectomy sigificantly enhanced pituitary responsiveness to a standard dose (2.0 microgram) of LH-RH, whereas the introduction of oestradiol-17 beta implants effectively inhibited the responses. LH-RH-induced LH release after gonadectomy (with and without oestradiol-17 beta treatment) was similar in males and females. The use of marmosets for appropriate investigation into the physiological role of LH-RH in controlling LH secretion in primates is proposed.     

Feedback control of FSH secretion in the male rat

Site of feedback control of FSH secretion in the male rat was studied by measuring changes in serum LH, FSH and hypothalamic LH-RH by radioimmunoassay in rats after castration and after 500 rad X-irradiation to the testis. The rise in serum LH and FSH in castrated animals was associated with a significant fall in hypothalamic LH-RH 16 and 24 days after castration. Serum FSH rose significantly after X-irradiation without a significant change in serum LH or hypothalamic LH-RH content up to 30 days after irradiation. When pituitary halves from X-irradiated animals were incubated in vitro in the presence or absence of synthetic LH-RH, there was a significant rise in FSH (but not LH) released in the incubation medium in the absence of added LH-RH. The response of the pituitaries to LH-RH was, however, not different between control and irradiated rats. It is concluded that the testicular FSH-inhibitory substance acts predominantly at the pituitary gland on the LH-RH independent release of FSH.     

Comparison between the biological effects of LH-RH and buserelin on the induction of LH release from hemi-pituitary glands of female rats in vitro

The biological effects of LH-RH and the agonist [D-Ser(But)6-des Gly10]-LH-RH(1-9)-ethylamide (buserelin) were compared during 8 h of incubation with female rat hemi-pituitary glands. Similar dose-response relationships were found for LH-RH and buserelin as concerns the release of luteinizing hormone (LH) by pituitary glands from intact and ovariectomized rats. Also the LH secretion patterns from glands of intact rats were similar: an initial low response was followed by a fast increase (priming effect) after which the response declined again (desensitization). In a subsequent experiment pituitary glands from ovariectomized rats were first exposed to LH-RH or buserelin for 4 h and then further incubated in medium only. After discontinuation of the stimuli the rate of LH release decreased in all cases, but this decrease was significantly greater when the glands had been exposed to LH-RH. Short-term (1/2, 1 or 2 h) exposures to LH-RH or buserelin followed by an intervening period (1 1/2, 1 or 0 h, respectively) of incubation in medium only resulted in an almost similar, significant increase in the subsequent protein synthesis-independent LH response to LH-RH (priming effect). Only preincubation with LH-RH for 2 h was significantly more effective. The results demonstrate equal intrinsic activities for LH-RH and buserelin. Differences in the biopotencies for LH-RH and buserelin in vivo and in vitro may occur only after discontinuation of the external stimuli.