Differential suppression of follicle-stimulating hormone and luteinizing hormone secretion in vivo by a gonadotropin-releasing hormone antagonist

Because of some indication that FSH secretion is less dependent than LH secretion on GnRH in vivo, we performed experiments to examine the effects of a GnRH antagonist (antag) on LH and FSH secretion. We first showed that pituitary cells superfused with GnRH showed a similar pattern of suppressed secretion of both LH and FSH in response to addition of antag. In contrast, antag administration to ovariectomized rats had differing effects on LH and FSH secretion. Serum LH was suppressed in a dose-dependent fashion by 2 h (20-50% of control values). Recovery from the lower doses of antag was seen by 12 h, but the two highest doses maintained serum LH levels at 10% of control values for 72 h. In contrast, the effect on serum FSH was not manifested until 12 h. FSH was maximally decreased only to 40-60% of control values. The two highest doses maintained this effect for 72 h. These results reinforce previous suggestions that FSH secretion in vivo may occur independently of acute changes in GnRH secretion, and may have an GnRH-independent component.     

Calcium-dependent actions of gonadotropin-releasing hormone agonist and luteinizing hormone upon cyclic AMP and progesterone production in rat ovarian granulosa cells

The Ca2+ dependency of the direct stimulatory effect of the gonadotropin-releasing hormone (GnRH) agonist analog [D-Ser(t-Bu)6]des-Gly10-GnRH-N-ethylamide (GnRHa) on progesterone production was investigated and compared to that of luteinizing hormone (LH) in rat granulosa cells from preovulatory follicles. Removal of extracellular Ca2+ by EGTA, or the use of the Ca2+ channel blockers verapamil and La3+, resulted in complete inhibition of GnRHa-induced progesterone production and a partial inhibition of LH-stimulated progesterone production (80, 80 and 50% inhibition respectively for EGTA, verapamil and La3+). Removal of extracellular Ca2+ increased the ED50 for LH-induced cAMP production by four-fold (from 80 to 330 ng/ml) and decreased maximal nucleotide formation by 44%. LH-induced cAMP production was also inhibited partially by verapamil (35%) at 10(-4) M drug concentration. GnRHa had no effect on cAMP production in the presence or absence of Ca2+. GnRHa and LH were found to have maximal effects on progesterone production at about 0.5 mM of Ca2+ in the incubation medium. On the other hand the stimulatory effect of dibutyryl cAMP [Bu)2cAMP) on progesterone production showed little dependency on extracellular Ca2+. The calmodulin antagonist trifluoperazine (TFP) caused concentration-dependent inhibition of the stimulatory action of GnRHa and LH on progesterone production with IC50 values of 3 and 8 microM, respectively. The stimulatory effect of (Bu)2cAMP on progesterone synthesis was attenuated by verapamil and TFP. These results indicate that the direct stimulatory effect of GnRH on ovarian progesterone production is absolutely dependent on Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadal luteinizing hormone receptors and adenylate cyclase: transfer of functional ovarian luteinizing hormone receptors to adrenal fasciculata cells.

Luteinized rat ovaries contain a high concentration of particulate luteinizing hormone (lutropin, LH) receptors and a small quantity of lipid-associated receptors that float in the 360,000 X g supernatant fraction of ovarian homogenates. During fractionation of Lubrol-solubilized LH receptors and adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] from the ovary and testis, LH receptors and adenylate cyclase were coincident on gel filtration, but could be resolved during ion-exchange chromatography of soluble ovarian preparations and were completely separated by lectin-affinity chromatography on Sepharose-concanavalin A. For further analysis of receptor-adenylate cyclase coupling, the lipid-rich fraction of ovarian luteal cells was used to transfer gonadal LH receptors to isolated adrenal fasciculata cells. The lipid vesicles obtained from ovarian homogenates by flotation at 360,000 X g contained 5--10% of the ovarian LH receptors and were devoid of adenylate cyclase activity. During incubation of lipid-associated receptors with dispersed rat fasciculata cells at 16 degrees C, progressive incorporation of LH binding sites into the adrenal cells was observed. When adrenal cells bearing heterotopic LH receptors were incubated with 1 nM human choriogonadotropin, cyclic AMP production was consistently stimulated, with an accompanying increase in corticosterone production. These results indicate that LH receptors exist as separate entities from adenylate cyclase in the gonadal cell membrane and can become functionally coupled to adenylate cyclase to evoke cyclic AMP production and steroidogenesis in the host adrenal cells to which they are transferred.     

Successful induction of ovulation and conception with combined gonadotropin-releasing hormone agonist plus highly purified follicle-stimulating hormone in patients with polycystic ovarian disease

Five women (group A) with polycystic ovarian disease (PCOD) and sterility for at least 3 yr were treated for 1 cycle for ovulation induction with a combined regimen of GnRH agonist (GnRH-A) plus highly purified FSH. The patients received GnRH-A (Buserelin; 200 micrograms, sc, twice a day) for 6 weeks and then GnRH-A combined with FSH highly purified (2 ampules a day; 75 IU FSH and less than 0.11 IU LH in each ampule). Ovarian response was evaluated by plasma estradiol (E2) assay and ultrasound examination, performed daily. Furthermore, plasma FSH and LH levels were assayed 3 times a week. Once a follicle was considered sufficiently developed, the combined regimen was withheld, and 24-48 h later hCG (5000 IU, im) was given. The results are compared with those of 31 ovulatory cycles induced by im FSH highly purified (group B) in PCOD patients with the same FSH administration, clinical, and monitoring protocols. Ovulation was achieved in all cycles treated by GnRH-A plus FSH. Two singleton and a twin pregnancy resulted. Multiple follicular development occurred in all cycles. Plasma E2 levels were generally in the normal range. Echographic and endocrine features in the 2 groups were as follows. 1) basal ovarian volume and ovarian enlargement were similar. 2) Group A had a greater number of follicles than did group B (P less than 0.01), while E2 to number of follicles and E2 to ovarian volume ratios were greater (P less than 0.01) in group B. 3) The linear correlations between plasma E2 levels and ovarian volume were markedly different in groups A and B (P less than 0.01). The regression line for group B had a steeper slope than that for group A. This finding indicates that at a fixed ovarian volume plasma E2 levels were significantly lower in group A than in group B. We conclude that the combined GnRH-A and FSH regimen may constitute an alternative and promising tool for the induction of ovulation in patients with PCOD.     

Serum bioactive and immunoreactive follicle-stimulating hormone in prostatic cancer patients during gonadotropin-releasing hormone agonist treatment and after orchidectomy

Serum bioactive and immunoreactive FSH levels were measured in five prostatic cancer patients during treatment for 6 months with the GnRH agonist analog buserelin (Hoechst; 600 micrograms, intranasally, 3 times per day) and for up to 12 weeks after subsequent orchidectomy. FSH bioactivity was measured using a sensitive specific in vitro granulosa cells aromatase bioassay. Before buserelin treatment, mean serum FSH bioactivity and immunoreactivity were 19.7 +/- 4.1 (+/- SE) IU/L (n = 5) and 13.7 +/- 3.8 IU/L, respectively, with a bioactivity to immunoactivity (B/I) ratio of 1.7 +/- 0.2. After the initiation of treatment with the GnRH agonist, FSH bio- and immunoactivities both transiently increased for 1-3 days. The increase in bioactivity was greater and prolonged, and the B/I ratio increased nearly 7-fold in 2 weeks. Serum FSH immunoreactivity declined to below the pretreatment level in 5 days and remained low for the rest of the treatment period. In contrast, serum FSH bioactivity did not decrease significantly below the pretreatment level during the 6-month treatment period, although the B/I ratio returned slowly toward the pretreatment value. After orchidectomy, both FSH activities increased dramatically, and the B/I ratio rose transiently from 1.5 to 7 in 2 weeks. Interestingly, serum FSH bioactivity and immunoreactivity decreased significantly (P less than 0.05) 1 day after orchidectomy in the buserelin-treated patients. In contrast, serum FSH immunoreactivity increased during the same period (P less than 0.05) in patients treated only by orchidectomy (FSH bioactivity was not measured). In conclusion, serum FSH bioactivity increases acutely more than FSH immunoreactivity after initiation of GnRH agonist treatment or orchidectomy. In the former case, serum FSH bioactivity subsequently returned to the pretreatment range. A clear decline during long term agonist treatment occurred only in serum FSH immunoreactivity, in contrast to the concomitant decline in serum LH bio- and immunoreactivities reported previously. The persistence of bioactive FSH may explain the inconsistent effects of GnRH agonist treatment on the suppression of spermatogenesis. The acute decrease in serum FSH after orchidectomy in the buserelin-treated men suggests that the testes may produce a factor that stimulates pituitary FSH secretion.     

Inhibitory effects of a gonadotropin-releasing hormone agonist on the luteal synthesis of progesterone, estradiol receptors, and prolactin surges during early pregnancy

Our recent studies demonstrated that the continuous administration of a GnRH agonist (GnRH-Ag; WY 40972) induces abortion in rats by suppressing plasma progesterone (P) levels within 24 h. This fall in P levels is not accompanied by a fall in ovarian venous plasma testosterone (T) or estradiol (E) levels. In this study an attempt was made 1) to determine whether the suppression of P by GnRH-Ag is due to decreased estrogen present in the corpora lutea (CL) and/or a decrease in luteal receptors of E, and 2) to investigate the effects of GnRH-Ag on the nocturnal surges of PRL. Rats were treated continuously on days 7-11 of pregnancy with 5 micrograms/day GnRH-Ag using an osmotic minipump. Ovarian blood samples were obtained on day 8; at autopsy CL were harvested and incubated with medium 199 for 4 h at 37 C under an atmosphere of 95% oxygen-5% carbon-dioxide. Additional rats were killed on day 8 or 10; CL were isolated from the ovary and pooled within the group for the measurement of nuclear and cytosolic E receptors. In other experiments, on days 8, 9, 10, and 11 of pregnancy, blood samples (0.3 ml) were collected via an indwelling intraatrial Silastic cannula at 0330, 0500, or 0600 h for the measurement of PRL and P. While the net synthesis of P by CL in the GnRH-Ag-treated rats decreased to 48 +/- 12 from 224 +/- 47 ng/CL in controls, T and E levels were not different from their respective control values. Steroid levels in ovarian venous plasma reflected a similar response. Nuclear E receptors levels were 82 and 80 in controls and 39 and 41 fmol/mg DNA in the treated group on days 8 and 10, respectively. Nocturnal surges of PRL in plasma were detected at 0330 h in controls as well as in treated rats. However, plasma PRL levels at 0330 h were 101 +/- 24, 120 +/- 22, 196 +/- 40, and 103 +/- 13 ng/ml in controls and 44 +/- 8, 50 +/- 10, 29 +/- 13, and 20 +/- 9 in the GnRH-Ag-treated group on days 8, 9, 10, and 11, respectively. These results suggest that GnRH-Ag has no effect on the ability of the luteal synthesis of T and E and that the antipregnancy effect of GnRH-Ag may be at the level of the CL due to the direct inhibitory effect of GnRH-Ag on the luteal synthesis of P, which, in turn, results in decreased nocturnal surges of PRL and a fall in E receptors in the CL. Alternatively, GnRH-Ag treatment could suppress ovarian or luteal receptors for PRL, which, in turn, lower luteal E receptors, leading to a fall in luteal synthesis and release of P.     

Comparative effects of cyproterone acetate or a long-acting gonadotropin-releasing hormone agonist in polycystic ovarian disease

A randomized cross-over study was done to compare the therapeutic efficacy of cyproterone acetate (CPA) and a depot preparation of the LHRH superagonist (DTrp6-LHRH) in 10 patients with polycystic ovarian disease (PCO). All patients were treated with both agents (50 mg/day CPA, orally and (3 mg DTrp6-LHRH, im, approximately once a month) for 3 months, the 2 treatment periods being separated by 6 months. Both treatments resulted in marked clinical improvement, with diminished acne and seborrhoea and normalization of ovarian size by ultrasonographic criteria. In response to CPA treatment, basal plasma gonadotropin levels decreased, but the response to a LHRH test was not completely suppressed. Plasma estradiol, estrone, testosterone, and androstenedione levels significantly decreased, but urinary 3 alpha-androstanediol and plasma dehydroepiandrosterone sulfate levels did not change significantly. In contrast to CPA treatment, both basal and stimulated gonadotropin levels were completely suppressed after 3 weeks of treatment with DTrp6-LHRH. After a slight initial evaluation on day 2, plasma estrogen and androgen levels, with the exception of dehydroepiandrosterone sulfate fell into the castrate range urinary 3 alpha-androstanediol excretion decreased significantly. Thus, in patients with PCO, LHRH-A induced more complete gonadotropin inhibition than did CPA. After cessation of either therapy, the disease rapidly recurred.     

Clinical and hormonal effects of chronic gonadotropin-releasing hormone agonist treatment in polycystic ovarian disease

Previously, we reported that short term administration of a highly potent GnRH agonist (GnRHa) for 1 month to patients with polycystic ovarian disease (PCO) resulted in complete suppression of ovarian steroidogenesis without measurable effects on adrenal steroid production. This new study was designed to evaluate the effects of long term GnRHa administration in PCO patients with respect to their hormone secretion patterns and clinical responses. Eight PCO patients and 10 ovulatory women with endometriosis were treated daily with sc injections of [D-His6-(imBzl]),Pro9-NEt]GnRH (GnRHa; 100 micrograms) for 6 months. Their results were compared to hormone values in 8 women who had undergone bilateral oophorectomies. In response to GnRHa, PCO and ovulatory women had rises of serum LH at 1 month, after which it gradually declined to baseline. In both groups FSH secretion was suppressed throughout treatment. Serum estradiol, estrone, progesterone, 17-hydroxyprogesterone, androstenedione, and testosterone levels markedly decreased to values found in oophorectomized women by 1 month and remained low thereafter. In contrast, serum pregnenolone and 17-hydroxypregnenolone were partially suppressed, and dehydroepiandrosterone, dehydroepiandrosterone sulfate, and cortisol levels did not change. Clinically, hyperplastic endometrial histology in three PCO patients reverted to an inactive pattern, and proliferative endometrium in two other PCO patients became inactive in one and did not change in the other. Regression of proliferative endometrial histology occurred in all ovulatory women. Vaginal bleeding occurred in all women studied during the first month of GnRHa administration, after which all but one PCO patient became amenorrheic. Hot flashes were noted by all ovulatory women and by four of eight PCO patients. All PCO patients noted subjective reduction of skin oiliness, and five had decreased hair growth. We conclude that in premenopausal women: 1) chronic GnRHa administration results in apparently complete persistent suppression of ovarian steroid secretion; 2) adrenal steroid secretion is not influenced directly or indirectly; and 3) its use may be helpful in the treatment of endometrial hyperplasia and ovarian androgen excess in women with PCO.     

Differing responses of plasma bioactive and immunoreactive follicle-stimulating hormone and luteinizing hormone to gonadotropin-releasing hormone antagonist and agonist treatments in postmenopausal women.

Plasma bioactive (B) and immunoreactive (I) FSH and LH were measured every 10 min for 8 h in the same postmenopausal women in a three-phase study: 1) during normal pulsatile gonadotropin secretion (basal study; n = 8), 2) 8 h after a single injection of a GnRH antagonist (5 mg Nal-Glu, sc; n = 5), and 3) 21 days after a GnRH agonist injection (D-Trp6, 3.75 mg depot preparation, im; n = 7). I-FSH and I-LH were measured by monoclonal antibody immunoradiometric assays. B-FSH and B-LH were measured in selected samples with the immature rat granulosa cell and mouse interstitial cell assays, respectively. Significant pulsatility of B- and I-FSH and LH was demonstrated in the basal samples, but only the B/I ratio of LH was slightly elevated within the secretion peaks. After GnRH antagonist treatment, I-FSH decreased from a mean pretreatment level of 55.7 +/- 7.8 IU/L by 26% (P less than 0.001), and B-FSH from 313.8 +/- 61.9 IU/L by 44% (P less than 0.01). The B/I ratio decreased from 6.4 +/- 1.7 to 4.5 +/- 1.0 (P less than 0.05). After agonist treatment, the I- and B-FSH levels decreased by 92% and 83% (P less than 0.0001), respectively, but the B/I ratio increased to 17.3 +/- 4.7 (P less than 0.05). The concentrations of I- and B-LH decreased by 75% and 80%, respectively (P less than 0.001), after antagonist treatment. After agonist treatment, I-LH decreased by 92%, and B-LH by 93% (P less than 0.0001). No changes in the B/I ratios of LH were found after either treatment. In conclusion, no changes were found in the quality of circulating LH during the treatments, whereas the antagonist treatment decreased and the agonist treatment increased the B/I ratio of FSH. These findings provide further evidence that the qualitative responses of FSH and LH to treatment with the same GnRH analog are different, and that the suppressive mechanisms of GnRH antagonist and agonist action on gonadotropin secretion are different.     

Recovery of hormone secretion after chronic gonadotropin-releasing hormone agonist administration in women with polycystic ovarian disease

Persistent suppression of gonadotropin and ovarian steroid production can be achieved in women with polycystic ovarian disease (PCO) by daily administration of a long-acting GnRH agonist (GnRHa). This study was designed to determine the patterns of recovery of clinical responses and hormonal secretion after chronic GnRHa administration in women with PCO. Six women with PCO were treated with daily sc injections of [D-His6(imBzl),Pro9-NEt]GnRHa (100 micrograms) for 6 months. Blood samples were obtained at the time of and three times weakly for 90 days after discontinuation of agonist therapy. In five women who did not ovulate, the suppressed serum FSH levels rose to pretreatment values within 10 days. In contrast, a gradual and progressive increase in serum LH (as measured by bioassay and immunoassay) was apparent by day 18. The LH increase coincided with progressive increases in serum estrone (E1), androstenedione, and testosterone. Serum estradiol (E2) began to rise on day 28. All hormones returned to their pretreatment baseline values within the 90-day recovery interval, with the exception of E2. Trend analysis of the slopes of recovery revealed that the incremental secretion patterns of E1, E2, androstenedione, and testosterone differed significantly from that of FSH, but not from those of bioactive or immunoactive LH. Serum progesterone, dehydroepiandrosterone sulfate, and cortisol did not change after withdrawal of GnRHa. One woman ovulated spontaneously on day 52 before which her hormone secretion patterns were indistinguishable from those of the other women. In summary, 1) during recovery after discontinuation of chronic GnRH agonist therapy the patterns of FSH and LH release suggested resumption of endogenous GnRH action on the pituitary with greater release of FSH than LH, a pattern that would be expected in the absence of ovarian steroid influence; 2) the lack of early estrogen production despite the increase in serum FSH concentrations suggests inadequate FSH secretion, abnormal ovarian responsiveness to FSH, or impaired FSH bioactivity; 3) androgen secretion was provoked by the increase in LH secretion; 4) per unit LH measured by bioassay, greater ovarian androgen secretion was stimulated in PCO than ovulatory women; and 5) the likelihood of spontaneous ovulation during recovery was minimal.     

Photoaffinity-labeling and fluorescence-distribution studies of gonadotropin-releasing hormone receptors in ovarian granulosa cells.

Photoaffinity labeling of rat ovarian granulosa cells and membrane preparations with a bioactive photoaffinity derivative of gonadotropin-releasing hormone resulted in identification of two specific components with apparent molecular weights of 60,000 and 54,000. Fluorescent visualization of gonadotropin-releasing hormone receptors in these cells, by using a bioactive rhodamine derivative of the hormone, indicated that the fluorescently labeled receptors were initially distributed uniformly on the cell surface and then formed patches that subsequently internalized (at 37 degrees C) into endocytic vesicles. These processes were dependent on specific binding sites for the rhodamine-labeled peptide on the granulosa cells. These studies may provide an experimental basis for understanding the molecular events involved in the action of the hormone in the ovary.     

The dependency of bioactive follicle-stimulating hormone secretion on gonadotropin-releasing hormone in hypogonadal and cycling women

An antagonist analog of GnRH, (Ac-delta 3-Pro1,p-F-D-Phe2,D-Trp3,6)GnRH (4F-antagonist), was administered to normal women and women with hypergonadotropic hypogonadism. Serum FSH levels were determined by both the granulosa cell aromatase bioassay and RIA. The constant infusion of 4F-antagonist (30 micrograms/kg.h) to the four hypogonadal women resulted in a more pronounced decline in bioactive FSH (62%) than in immunoreactive FSH levels (30%), and the FSH bioactive to immunoreactive ratio decreased significantly (P less than 0.05). Infusion of 4F-antagonist in normal women in the midfollicular phase revealed a similar pattern of suppression of bioactive (64%) and immunoreactive FSH (29%). When 4F-antagonist was administered sc at a dose of 80 micrograms/kg twice daily for 3 days to normal women in the midfollicular phase of their cycles, the bioactive FSH response was biphasic, with the maximal decrease on the second day, followed by return to basal levels on the third day. Correspondingly, there was a precipitous decline in serum estradiol (apparent demise of the dominant follicle), followed by a progressive rise in estradiol levels. Thus, in contrast to immunoreactive FSH levels, bioactive FSH more clearly reflects the biological action of FSH on the follicle in response to GnRH antagonist administration in women. The disparity in the quantitative decline between serum bioactive and immunoreactive FSH levels after presumed blockade of the GnRH receptor may reflect the microheterogeneity of the FSH molecule and suggests that alterations in the biological activity of secreted FSH may be GnRH dependent.     

Reduction of gonadotropin-releasing hormone pulse frequency is associated with subsequent selective follicle-stimulating hormone secretion in women with polycystic ovarian disease

Polycystic ovarian disease (PCO) is characterized by hyperandrogenism, ovulatory dysfunction, and altered gonadotropin secretion. Mean plasma FSH concentrations are low, while LH is elevated in a majority of patients. LH pulsatile secretion has been shown to occur at rapid follicular phase frequencies (approximately one pulse per h) in PCO, suggesting persistent rapid frequency GnRH secretion in this disorder. Anovulatory women with PCO were given estradiol (E2; Estraderm skin patches) and progesterone (P; vaginal suppositories) to produce midluteal concentrations for 21 days. The aim was to determine if E2 and P would slow LH (GnRH) pulse frequency and if this would result in augmented FSH secretion and follicular development after withdrawal of E2 and P. Plasma LH was measured every 10 min for 8 h before, during (days 10 and 20), and 7 days after withdrawal of E2 and P (day 28). On each of these study days FSH was measured hourly, and E2 and P were measured every 2 h. After sampling, GnRH (25 and 250 ng/kg, iv) was given to assess pituitary responsiveness. Follicular development was monitored by vaginal ultrasound through day 34 of the study. Basal LH frequency was 8.5 +/- 0.5 pulses/8 h (mean +/- SEM). During E2 and P, LH pulse frequency fell to 3.3 +/- 1.0 (10 days) and 2.3 +/- 0.8 (20 days), 39% and 27% of the basal value, respectively, and subsequently increased to 5.6 +/- 0.7 (66% of basal) 7 days after withdrawal of E2 and P. LH pulse amplitude (basal, 7.2 +/- 1.5 IU/L) was not reduced until day 20, but remained suppressed (3.9 +/- 1.1 IU/L) on day 28. As a result, mean LH (basal, 21.0 +/- 3.5 IU/L) fell progressively during E2 and P, to 3.8 +/- 1.2 IU/L on day 20, and remained low (39% of basal) 7 days after steroid withdrawal. Mean plasma FSH (basal, 7.1 +/- 0.9 IU/L) also fell during steroid administration, but in contrast to LH, had risen to 93% of the basal value by 7 days after E2 and P. LH release in response to exogenous GnRH revealed marked initial responses which did not decrease until day 20, but remained suppressed (8% of basal) after withdrawal of E2 and P. FSH responses were also suppressed on day 20, but had increased to 75% of the basal value by day 28. Initiation of follicular development occurred in all patients, and the lead follicle measured 12.3 +/- 0.8 mm 13 days post-E2 and P. Ovulation occurred in one patient.(ABSTRACT TRUNCATED AT 400 WORDS)     

Persistence of hyperinsulinemia in polycystic ovary syndrome after ovarian suppression by gonadotropin-releasing hormone agonist.

To investigate the effect of long-term androgen suppression on insulin sensitivity, obese and non-obese women with the polycystic ovary syndrome and obese and non-obese ovulatory women were given an oral glucose tolerance test before and after treatment with a gonadotropin-releasing hormone agonist. The women with polycystic ovary syndrome showed higher basal luteinizing hormone and androgen levels than the ovulatory women. All women with the polycystic ovary syndrome responded non-diabetically to the glucose tolerance test. However, compared with controls, the obese women with the polycystic ovary syndrome showed a hyperinsulinemic response to the glucose tolerance test, indicating insulin resistance. During the 3-h glucose tolerance test there was no concomitant change in androgen levels in the hyperinsulinemic women with the polycystic ovary syndrome. The insulin response to an oral glucose tolerance test remained unchanged in all women, although a hypogonadotropic hypogonadal state was maintained for several weeks. This study therefore suggests that endogenous androgens do not play a role in sustaining insulin resistance in women with the polycystic ovary syndrome.     

Topographic separation of adenylate cyclase and hormone receptors in the plasma membrane of toad erythrocyte ghosts

Brief sonication of whole erythrocyte plasma membranes (ghosts) from toads at 4 degrees does not inactivate adenylate cyclase [ATP pyrophosphate-lyase (cyclizing); EC 4.6.1.1] or destroy the receptor binding properties of hydroxybenzylpindolol or insulin. The hormonal (but not the fluoride-induced) stimulation of this enzyme is, however, lost. Fractionation of the small, resealed membrane fragments (vesicles) on discontinuous sucrose gradients results in the separation of vesicle populations differing grossly in size and protein composition. In addition, the distribution of the beta-adrenergic receptor, an insulin binding site, and adenylate cyclase among these vesicles fractions differs. The pattern of distribution of these functional structures can be altered differentially by manipulations of the ghosts before sonication. For example, brief preincubation with isoproterenol leads to a change in the relative distribution of beta-receptor (but not adenylate cyclase) among the various vesicle fractions; this effect is not obtained with beta-receptor antagonists, which block the isoproterenol effect. Exposure of the ghosts to different temperatures, changes in the divalent cation composition of the medium, or the addition of ATP also leads to changes in the distribution of surface markers of the subsequently formed vesicles. The results indicate gross asymmetries in the distribution of protein components within the plane of the membrane and raise important questions regarding the manner whereby functionally related and coupled components, such as hormone receptors and adenylate cyclase, interact.     

The stimulatory and down-regulatory effects of a gonadotropin-releasing hormone agonist in man

Synthetic long-acting agonistic analogs of GnRH both stimulate and paradoxically inhibit gonadotropin secretion in male animals and humans. To characterize the stimulatory and down-regulatory effects of such a superactive GnRH analog in man, either 10 or 100 micrograms D-( Nal2 ) 6GnRH were administered sc to two groups of seven normal men for 10 days. Serum LH, FSH, and testosterone were determined daily before analog injection and 1, 2, 4, 6, 8, 12, 16, and 24 h after analog injection on days 1 and 10. Both doses of analog led to initial increases in LH, FSH (peak, days 2-3), and testosterone (peak, days 3-4), but by day 10 of analog administration, serum levels of LH, FSH, and testosterone returned to pretreatment levels. The integrated 24-h responses above baseline of serum LH and FSH to both doses of GnRH analog were significantly decreased on day 10 compared to day 1 (P less than 0.05). The integrated 24-h responses of serum testosterone to both doses of agonist were not significantly decreased on day 10 of agonist treatment compared to those on day 1 (P greater than 0.2). Integrated serum testosterone responses above baseline in response to 3000 IU hCG administered 2 weeks before analog treatment and 24 h after the last analog injection were not different (P greater than 0.2). GnRH agonist treatment resulted in proportionate stimulation of LH, FSH, and testosterone consistent with a predominant pituitary effect of the analog at these doses given for 10 days. The stimulatory effects of daily GnRH agonist treatment in men are transient with some down-regulatory effects evident after 10 days of treatment.     

Pituitary binding and internalization of radioiodinated gonadotropin-releasing hormone agonist and antagonist ligands in vitro and in vivo

In rat pituitary gonadotrophs, the rates of binding and endocytosis of two GnRH superagonist analogs, [D-Ala6,Pro9-NEt]GnRH and [D-Lys6,Pro9-NEt]GnRH, were compared with those of the potent antagonist analog [N-acetyl-D-pCl-Phe1,2,D-Trp3,D-Lys6,D-Ala10]GnRH by quantitative electron microscopic autoradiography. In dispersed pituitary cells, the two agonist analogs showed similar binding kinetics and comparable degrees of sequestration, as measured by their resistance to dissociation by low pH buffer. However, quantification of silver grain localization suggested that cellular internalization of the [D-Ala6]GnRH agonist increased more rapidly than that of the [D-Lys6]GnRH analog. These discrepancies, and the finding that a larger amount of the specifically bound 125I-[D-Ala6]GnRH agonist was removed during glutaraldehyde fixation, indicated that the proportional internalization of this analog was over estimated by quantitative autoradiography owing to loss of cell surface-bound radioligand. We, therefore, employed radioiodinated D-Lys6-substituted analogs to analyze the receptor binding and cellular uptake of GnRH agonist and antagonist derivatives in vivo. After iv injection, a high proportion of the 125I-[D-Lys6]GnRH agonist was translocated into pituitary gonadotrophs within 60 min, whereas the D-Lys6 antagonist was predominantly associated with the plasma membrane during that time. Four hours after injection of the antagonist, an appreciable proportion of silver grains was associated with intracellular organelles, and this trend increased progressively at later time points. The relatively prolonged cellular processing of the GnRH antagonist is consistent with in vivo binding kinetics, and its slower internalization may reflect the basal rate of GnRH receptor turnover in the cell membrane. In addition, the marked difference between the rates of internalization of the bound [D-Lys6]GnRH agonist and antagonist ligands supports the proposal that receptor activation is responsible for the rapid endocytosis of agonist ligands by the GnRH-stimulated pituitary gonadotroph.