Effect of gonadotropin-inhibitory hormone on luteinizing hormone secretion in humans.

BACKGROUND: Gonadotropin-inhibitory hormone (GnIH, human homologue of RFRP-3) suppresses gonadotropin secretion in animal models, but its effects have not been studied in the human. OBJECTIVE: We tested the hypotheses that exogenous GnIH inhibits LH secretion (i) in postmenopausal women and (ii) in men concurrently administered exogenous kisspeptin. DESIGN: Following in vitro and in vivo preclinical studies to functionally characterize the GnIH peptide, a dose-finding study (human GnIH: 1·5-150 µg/kg/h, iv for 3 h) was undertaken, and 50 µg/kg/h selected for further evaluation. Five postmenopausal women were administered 50 µg/kg/h iv infusion for 3 h or vehicle on two separate days. Four men were administered kisspeptin-10 (0·3 µg/kg iv bolus) with simultaneous infusion of GnIH (50 µg/kg/h, iv for 3 h) or vehicle. PARTICIPANTS: Healthy postmenopausal women (mean age 58 ± 2 years, LH: 30·8 ± 2·9 IU/l, FSH: 78·7 ± 6·4 IU/l, oestradiol: <50 pmol/l) and men (39·8 ± 2·1 years, mean total testosterone 12·1 ± 1·8 nmol/l, LH 2·2 ± 0·2 IU/l). PRIMARY OUTCOME: Change in area under curve (AUC) of LH during GnIHvs vehicle. RESULTS: During GnIH administration in postmenopausal women, LH secretion decreased (ΔAUC: -9·9 ± 1·8 IU/3 h) vs vehicle (ΔAUC: -0·5 ± 1·7 IU/3 h; P = 0·02). Kisspeptin-10-stimulated LH responses in men were not affected by GnIH co-administration (60-min AUC of LH 6·2 ± 0·8 IU/h with kisspeptin-10 alone, 6·3 ± 1·0 IU/h, kisspeptin-10 with GnIH, P = 0·72). Exogenous GnIH was well tolerated, with no adverse events reported. CONCLUSIONS: Gonadotropin-inhibitory hormone decreased LH secretion in postmenopausal women in this first-in-human study. Kisspeptin-stimulated LH secretion in men was not inhibited during concomitant administration of GnIH.

Hyperphagia in male melanocortin 4 receptor deficient mice promotes growth independently of growth hormone.

KEY POINTS: Loss of function of the melanocortin 4 receptor (MC4R) results in hyperphagia, obesity and increased growth. Despite knowing that MC4Rs control food intake, we are yet to understand why defects in the function of the MC4R receptor contribute to rapid linear growth. We show that hyperphagia following germline loss of MC4R in male mice promotes growth while suppressing the growth hormone-insulin-like growth factor-1 (GH-IGF-1) axis. We propose that hyperinsulinaemia promotes growth while suppressing the GH-IGF-1 axis. It is argued that physiological responses essential to maintain energy flux override conventional mechanisms of pubertal growth to promote the storage of excess energy while ensuring growth. ABSTRACT: Defects in melanocortin-4-receptor (MC4R) signalling result in hyperphagia, obesity and increased growth. Clinical observations suggest that loss of MC4R function may enhance growth hormone (GH)-mediated growth, although this remains untested. Using male mice with germline loss of the MC4R, we assessed pulsatile GH release and insulin-like growth factor-1 (IGF-1) production and/or release relative to pubertal growth. We demonstrate early-onset suppression of GH release in rapidly growing MC4R deficient (MC4RKO) mice, confirming that increased linear growth in MC4RKO mice does not occur in response to enhanced activation of the GH-IGF-1 axis. The progressive suppression of GH release in MC4RKO mice occurred alongside increased adiposity and the progressive worsening of hyperphagia-associated hyperinsulinaemia. We next prevented hyperphagia in MC4RKO mice through restricting calorie intake in these mice to match that of wild-type (WT) littermates. Pair feeding of MC4RKO mice did not prevent increased adiposity, but attenuated hyperinsulinaemia, recovered GH release, and normalized linear growth rate to that seen in pair-fed WT littermate controls. We conclude that the suppression of GH release in MC4RKO mice occurs independently of increased adipose mass, and is a consequence of hyperphagia-associated hyperinsulinaemia. It is proposed that physiological responses essential to maintain energy flux (hyperinsulinaemia and the suppression of GH release) override conventional mechanisms of pubertal growth to promote the storage of excess energy while ensuring growth. Implications of these findings are likely to extend beyond individuals with defects in MC4R signalling, encompassing physiological changes central to mechanisms of growth and energy homeostasis universal to hyperphagia-associated childhood-onset obesity.

Adolescent growth: genes, hormones and the peer group. Proceedings of the 20th Aschauer Soiree, held at Glücksburg castle, Germany, 15th to 17th November 2013.

The association between poverty, malnutrition, illness and poor socioeconomic conditions on the one side, and poor growth and short adult stature on the other side, is well recognized. Yet, the simple assumption by implication that poor growth and short stature result from poor living conditions, should be questioned. Recent evidence on the impact of the social network on adolescent growth and adult height further challenges the traditional concept of growth being a mirror of health. Twenty-nine scientists met at Glücksburg castle, Northern Germany, November 15th - 17th 2013, to discuss genetic, endocrine, mathematical and psychological aspects and related issues, of child and adolescent growth and final height.

A single injection of kisspeptin-54 temporarily increases luteinizing hormone pulsatility in healthy women.

BACKGROUND: Kisspeptin is a novel hypothalamic peptide which stimulates endogenous gonadotrophin releasing hormone (GnRH) secretion. A single subcutaneous bolus injection of kisspeptin-54 increases circulating luteinizing hormone (LH) levels in women, but its acute effects on LH pulsatility are not known. AIMS: To investigate the effects of a single subcutaneous (sc) injection of kisspeptin-54 administration on LH pulsatility in healthy female volunteers. METHODS: Six healthy female adult volunteers underwent 10-minute blood sampling for serum LH measurement for 8 h during the follicular phase of menstrual cycle. Sc bolus injection of saline or kisspeptin-54 (0·15, 0·30 or 0·60 nmol/kg) was administered 4 h after commencing the study. A previously described, blinded deconvolution method was used to detect LH pulses. RESULTS: Mean number of LH pulses was increased significantly following 0·30 and 0·60 nmol/kg kisspeptin-54 when compared with saline (mean increase in number of LH pulses per 4 h, following injection: -0·17 ± 0·54, saline; +2·33 ± 0·56, 0·30 nmol/kg kisspeptin-54, P < 0·05 vs saline; +2·33 ± 0·80, 0·60 nmol/kg kisspeptin-54, P < 0·05 vs saline). LH pulse secretory mass increased following injection of 0·60 nmol/kg in five of six subjects, but the mean change in all subjects was non-significant when compared with saline (mean increase in pulse secretory mass in IU/l following injection: +0·35 ± 0·40, saline; +2·61 ± 1·17, 0·60 nmol/kg kisspeptin-54, P = 0·10 vs saline). CONCLUSIONS: A single injection of kisspeptin-54 temporarily stimulates the number of LH pulses in healthy women. Further studies are required to investigate the therapeutic potential of kisspeptin-54 injection to restore LH pulsatility in patients with reproductive disorders caused by impaired GnRH secretion.

Hyperglycaemia is associated with impaired pulsatile insulin secretion: effect of basal insulin therapy.

AIM: Postprandial insulin pulsatility is impaired in patients with type 2 diabetes, but the effects of exogenous insulin therapy on pulsatile insulin secretion are not known. We addressed, whether pulsatile insulin secretion is related to glycaemic control, whether basal insulin supplementation increases postprandial insulin secretion, and if so, is this accomplished by a specific improvement in pulsatile insulin secretion? METHODS: Fourteen patients with type 2 diabetes underwent a mixed meal test before and after an 8-week treatment period with insulin glargine. Glucose, insulin and C-peptide levels were measured, and insulin pulsatility was determined by deconvolution analysis. RESULTS: Insulin treatment lowered fasting glycaemia from 179.6 ± 7.5 mg/dl to 117.6 ± 6.5 mg/dl (p < 0.001). Postprandial insulin and C-peptide levels increased significantly after the treatment period (p < 0.0001). The total calculated insulin secretion rate increased with insulin treatment (p = 0.0039), with non-significant increases in both pulsatile and non-pulsatile insulin secretion. Insulin pulse frequency was unchanged by the intervention. There was an inverse relationship between fasting and postprandial glycaemia and insulin pulse mass (r(2) = 0.51 and 0.56, respectively), whereas non-pulsatile insulin secretion was unrelated to either fasting or postprandial glucose concentrations (r(2) = 0.0073 and 0.031). CONCLUSIONS: Hyperglycaemia in type 2 diabetes is associated with a reduction in postprandial insulin secretion, specifically through a reduction in insulin pulsatility. Reducing chronic hyperglycaemia by basal insulin therapy enhances endogenous ß-cell function in the postprandial state. These data support the use of basal insulin regimens in the pharmacotherapy of overtly hyperglycaemic patients with type 2 diabetes.

Pathophysiology of hypercortisolism in depression: pituitary and adrenal responses to low glucocorticoid feedback.

OBJECTIVE: To test three theories of hypercortisolemia in depression-hypothalamic overdrive, impaired glucocorticoid feedback, or autonomous cortisol production. METHOD: We applied an overnight low-cortisol feedback strategy by administering metyrapone to hypercortisolemic depressed in-patients and control subjects. RESULTS: Under metyrapone, the increases of plasma adrenocorticotropic hormone (ACTH) concentrations and of basal and pulsatile ACTH secretion were not exaggerated in hypercortisolemic depressed patients compared with control subjects. ACTH approximate entropy (ApEn) did not differ at baseline or under metyrapone. Thus, neither hypothalamic overdrive nor irregular ACTH secretion was seen. We did not detect impaired cortisol feedback: the ACTH response was not reduced, and ApEn measures that are sensitive to feedback changes were comparable in both groups. Metyrapone disrupted cortisol secretory regularity in depressed and control subjects. On the baseline day, basal cortisol secretion was significantly increased and was highly irregular (high ApEn), and ACTH-cortisol cross-ApEn was markedly elevated in high-cortisol patients. CONCLUSION: Classical feed-forward overdrive and impaired feedback theories of hypercortisolemia in depression were not supported. Depressive hypercortisolemia may result from alternative pathophysiological mechanisms involving irregular basal hypersecretion of cortisol, associated with adrenal enlargement, possibly through splanchnic sympathetic activation of the adrenal cortex.

Saltation and stasis: a model of human growth.

Human growth has been viewed as a continuous process characterized by changing velocity with age. Serial length measurements of normal infants were assessed weekly (n = 10), semiweekly (n = 18), and daily (n = 3) (19 females and 12 males) during their first 21 months. Data show that growth in length occurs by discontinuous, aperiodic saltatory spurts. These bursts were 0.5 to 2.5 centimeters in amplitude during intervals separated by no measurable growth (2 to 63 days duration). These data suggest that 90 to 95 percent of normal development during infancy is growth-free and length accretion is a distinctly saltatory process of incremental bursts punctuating background stasis.

Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human.

During the last decade, the GH axis has become the compelling focus of remarkably active and broad-ranging basic and clinical research. Molecular and genetic models, the discovery of human GHRH and its receptor, the cloning of the GHRP receptor, and the clinical availability of recombinant GH and IGF-I have allowed surprisingly rapid advances in our knowledge of the neuroregulation of the GH-IGF-I axis in many pathophysiological contexts. The complexity of the GHRH/somatostatin-GH-IGF-I axis thus commends itself to more formalized modeling (154, 155), since the multivalent feedback-control activities are difficult to assimilate fully on an intuitive scale. Understanding the dynamic neuroendocrine mechanisms that direct the pulsatile secretion of this fundamental growth-promoting and metabolic hormone remains a critical goal, the realization of which is challenged by the exponentially accumulating matrix of experimental and clinical data in this arena. To the above end, we review here the pathophysiology of the GHRH somatostatin-GH-IGF-I feedback axis consisting of corresponding key neurotransmitters, neuromodulators, and metabolic effectors, and their cloned receptors and signaling pathways. We propose that this system is best viewed as a multivalent feedback network that is exquisitely sensitive to an array of neuroregulators and environmental stressors and genetic restraints. Feedback and feedforward mechanisms acting within the intact somatotropic axis mediate homeostatic control throughout the human lifetime and are disrupted in disease. Novel effectors of the GH axis, such as GHRPs, also offer promise as investigative probes and possible therapeutic agents. Further understanding of the mechanisms of GH neuroregulation will likely allow development of progressively more specific molecular and clinical tools for the diagnosis and treatment of various conditions in which GH secretion is regulated abnormally. Thus, we predict that unexpected and enriching insights in the domain of the neuroendocrine pathophysiology of the GH axis are likely be achieved in the succeeding decades of basic and clinical research.

Are estrogens of import to primate/human ovarian folliculogenesis?

The notion that estrogens play a meaningful role in ovarian folliculogenesis stems from a large body of in vitro and in vivo experiments carried out in certain rodent models, (e.g., rats) wherein the stimulatory role of estrogen on granulosa cell growth and differentiation is undisputed. However, evidence derived from these polyovulatory species may not be readily generalizable to the monoovulatory subhuman primates, let alone the human. Only recently, significant observations on the ovarian role(s) of estrogen have been reported for the primate/human. It is thus the objective of this communication to review the evidence for and against a role for estrogens in primate/human ovarian follicular development with an emphasis toward the application of the concepts so developed to contemporary reproductive physiology and to the practice of reproductive medicine. The role(s) of estrogens will be examined not only by analyzing the physiological evidence to the effect that these hormones control ovarian function and follicular growth, but also by summarizing the molecular evidence for the existence and distribution of the cognate receptors.

Adrenal, thyroid and gonadal axes are affected at high altitude.

Humans cannot live at very high altitude for reasons, which are not completely understood. Since these reasons are not restricted to cardiorespiratory changes alone, changes in the endocrine system might also be involved. Therefore, hormonal changes during prolonged hypobaric hypoxia were comprehensively assessed to determine effects of altitude and hypoxia on stress, thyroid and gonadal hypothalamus-pituitary hormone axes. Twenty-one male and 19 female participants were examined repetitively during a high-altitude expedition. Cortisol, prolactin, thyroid-stimulating hormone (TSH), fT4 and fT3 and in males follicle-stimulating hormone (FSH), luteinizing hormone (LH) and total testosterone were analysed as well as parameters of hypoxemia, such as SaO2 and paO2 at 550 m (baseline) (n = 40), during ascent at 4844 m (n = 38), 6022 m (n = 31) and 7050 m (n = 13), at 4844 m (n = 29) after acclimatization and after the expedition (n = 38). Correlation analysis of hormone concentrations with oxygen parameters and with altitude revealed statistical association in most cases only with altitude. Adrenal, thyroid and gonadal axes were affected by increasing altitude. Adrenal axis and prolactin were first supressed at 4844 m and then activated with increasing altitude; thyroid and gonadal axes were directly activated or suppressed respectively with increasing altitude. Acclimatisation at 4844 m led to normalization of adrenal and gonadal but not of thyroid axes. In conclusion, acclimatization partly leads to a normalization of the adrenal, thyroid and gonadal axes at around 5000 m. However, at higher altitude, endocrine dysregulation is pronounced and might contribute to the physical degradation found at high altitude.

Estradiol modulates the pulsatile secretion of biologically active luteinizing hormone in man.

We investigated the effects of estradiol on bioactive luteinizing hormone (LH) release in normal men using two complementary strategies: (i) steady state intravenous infusions of estradiol at its endogenous production rate, and (ii) oral administration of the antiestrogen, tamoxifen HCl. Immunoreactive and biologically active LH were monitored by radioimmunoassay and the rat interstitial cell testosterone bioassay, respectively. Estradiol infusions significantly suppressed mean plasma bioactive LH concentrations and decreased the bio/immuno LH ratio. Conversely, antiestrogen treatment enhanced spontaneous bioactive LH pulse frequency, increased bioactive LH pulse amplitude, and augmented plasma intrapulse and interpulse bio/immuno LH ratios. Low-dose pulsed injections of exogenous gonadotropin-releasing hormone (GnRH) also increased plasma bio/immuno LH ratios. However, tamoxifen attenuated the ability of exogenous GnRH to further enhance the bio/immuno LH ratio, which suggests that endogenous LH release was already maximally enriched in LH bioactivity during antiestrogen administration. We conclude that estradiol modulates the pulsatile secretion of LH molecules enriched in biological activity in man.

Endogenous opiates modulate the pulsatile secretion of biologically active luteinizing hormone in man.

We studied the secretion of physiological pools of immunoreactive and biologically active luteinizing hormone in response to endogenous pulses of gonadotropin-releasing hormone (GNRH) in eugonadal men. Concentrations of immunoactive and bioactive luteinizing hormone (LH) were determined in blood drawn at 20-min intervals for 8 h in eight normal men under two conditions: (a) after placebo, in order to evaluate spontaneous LH pulsations in the basal state, and (b) after administration of the opiate-receptor antagonist, naltrexone, which is believed to amplify the pulsatile release of endogenous GNRH. Spontaneous and naltrexone-stimulated secretion of LH occurred in pulses of high biological activity, as measured in the RICT (rat interstitial cell testosterone bioassay), i.e., bioactive:immunoactive LH ratios within both spontaneous and naltrexone-stimulated LH pulses were higher than corresponding interpulse ratios (P less than 0.001). Quantitative characterization of the pulsatile release of bioactive LH revealed the following specific effects of opiate-receptor blockade: increased 8-h mean and integrated serum concentrations of bioactive LH (P less than 0.002), enhanced pulse frequency of bioactive LH release (P less than 0.001), and augmented peak amplitude of bio-LH pulses (P less than 0.01). Moreover, this increase in episodic secretion of bioactive LH was associated with increased 8-h mean and integrated serum testosterone concentrations in these men (P less than 0.05). We conclude the following: (a) LH is normally released in spontaneous pulses of high biological activity in men; (b) when the endogenous GNRH signal is amplified by opiate-receptor blockade, the pituitary gland releases more frequent bioactive LH pulses, which are of high amplitude and contain a high bioactive:immunoactive LH ratio. This increase in pulsatile release of bioactive LH quantitated in the RICT assay in vitro is reflected by acutely increased serum testosterone concentrations in vivo. We infer that modulation of the episodic GNRH signal by endogenous opiates provides another significant mechanism by which the hypothalamus can alter the biological activity of circulating gonadotropic hormone in man. Moreover, observed alterations in the pulsatile pattern of bioactive LH release were associated in turn with significant changes in testosterone concentrations. Thus, we hypothesize that alterations in the properties of the bioactive LH pulse signal can provide an important mechanism for regulating target-cell function within the gonad in states of health or disease.

Role of endogenous opiates in the expression of negative feedback actions of androgen and estrogen on pulsatile properties of luteinizing hormone secretion in man.

We have tested the participation of endogenous opiate pathways in the negative feedback actions of gonadal steroids on pulsatile properties of luteinizing (LH) hormone release in normal men. To this end, sex steroid hormones were infused intravenously at dosages that under steady state conditions selectively suppressed either the frequency or the amplitude of the pulsatile LH signal. The properties of pulsatile LH secretion were assessed quantitatively by computerized analysis of LH series derived from serial blood sampling over 12 h of observation. When the pure (nonaromatizable) androgen, 5-alpha-dihydrotestosterone, was infused continuously for 108 h at the blood production rate of testosterone, we were able to achieve selective inhibition of LH pulse frequency akin to that observed in experimental animals after low-dosage androgen replacement. Under these conditions, serum concentrations of testosterone and estradiol-17 beta did not change significantly, but serum 5 alpha-dihydrotestosterone concentrations increased approximately two- to threefold, with a corresponding increase in levels of its major metabolite, 5 alpha-androstan-3 alpha, 17 beta-diol. In separate experiments, the infusion of estradiol-17 beta at its blood production rate over a 4.5-d interval selectively suppressed LH pulse amplitude without influencing LH pulse frequency. Estrogen infusion increased serum estradiol-17 beta levels approximately twofold without significantly altering blood androgen concentrations. We then used these schedules of selective androgen or estrogen infusion to investigate the participation of endogenous opiates in the individual inhibitory feedback actions of pure androgen or estrogen on pulsatile LH release by administering a potent and specific opiate-receptor antagonist, naltrexone, during the infusions. Our observations indicate that, despite the continuous infusion of a dosage of 5 alpha-dihydrotestosterone that significantly suppresses LH pulse frequency, co-administration of an opiate-receptor antagonist effectively reinstates LH pulse frequency to control levels. Moreover, during the infusion of a suppressive dose of estradiol-17 beta, opiate receptor blockade significantly augments LH pulse frequency and increases LH peak amplitude to control levels. Thus, the present studies in normal men demonstrate for the first time that the selective inhibitory action of a pure androgen on LH pulse frequency is effectively antagonized by opiate-receptor blockade. This pivotal observation indicates that opiatergic and androgen-dependent mechanisms specifically and coordinately control the hypothalamic pulse generator for gonadotropin-releasing hormone (GnRH)

Attenuated release of biologically active luteinizing hormone in healthy aging men.

To examine the biological quality and physiologically pulsatile mode of endogenous luteinizing hormone release in active, healthy aging men, we used the rat interstitial-cell testosterone in vitro bioassay to probe LH bioactivity in response to (a) endogenous gonadotropin-releasing hormone (GnRH) action (basal pulsatile bioactive LH secretion); (b) exogenous GnRH stimulation (10 micrograms IV pulses); and (c) inhibition of endogenous estrogen negative feedback (treatment with a nonsteroidal antiestrogen, tamoxifen). Basally, some healthy older men exhibited evidence of neuroendocrine dysfunction, reflected by irregular bursts of bioactive LH release followed by transiently low plasma bio:immuno (B:I) LH ratios. However, mean basal plasma bioactive LH concentrations, B:I ratios, and spontaneous LH pulse properties (peak frequency, amplitude, duration, and enhanced B:I ratios within LH peaks) were not altered in older men. On the other hand, augmentation of bioactive LH secretion and enhancement of plasma B:I ratios by pulsed injections of exogenous GnRH were either significantly reduced or absent in older men. In addition, although tamoxifen increased bioactive LH pulse frequency in both age groups and facilitated exogenous GnRH action in some subjects, older men increased their 12-h mean bioactive LH concentrations, B:I ratios, and bioactive LH peak amplitudes to a significantly lesser degree than young men. In summary, young and older healthy men exhibit similar mean basal plasma bioactive LH concentrations and spontaneous LH pulse properties. However, pituitary bioactive LH reserve is markedly attenuated in older men challenged with either exogenous GnRH or antiestrogen. Accordingly, we conclude that healthy aging men manifest an impaired secretory reserve for biologically active LH release.

Metabolic clearance of biologically active luteinizing hormone in man.

The plasma metabolic clearance of biologically active luteinizing hormone (bioactive LH) was studied using the rat interstitial cell testosterone (RICT) bioassay in six hypogonadotropic men after single bolus injection of highly purified human LH and during continuous steady-state infusions of three graded doses of LH. The LH bolus disappearance curves provided estimates of metabolic clearance rates (MCR) of 24.1 +/- 4.7 (+/- SD) ml/min for bioactive LH vs. 56.2 +/- 12 ml/min for immunoactive LH in the same men (P = 0.03). A lower MCR of bioactive LH compared with immunoactive LH was also observed during continuous infusions of physiological doses of LH; for example, the mean steady-state MCRs for bioactive and immunoactive LH were, respectively, 26.1 +/- 3.1 and 34.2 +/- 3.2 ml/min (P = 0.02). Moreover, the stepped-dose infusion regimens permitted us to demonstrate that increasing doses of pure human LH resulted in progressive and parallel decreases in the apparent MCRs of both bioactive and immunoactive LH. Based on the respective steady-state MCRs calculated at physiological plasma concentrations of immunoactive and bioactive LH, we estimate a mean endogenous production rate for bioactive hormone of 1,937 IU/24 h, and for immunoactive LH of 589 IU/24 h in normal men. These results indicate that previous estimates of LH production rates from immunoassay data alone markedly underestimate the quantity of biologically active hormone secreted in man.

Preservation of androgen secretion during estrogen suppression with aminoglutethimide in the treatment of metastatic breast carcinoma.

We evaluated the comparative effects of aminoglutethimide (AG) on androgen and estrogen levels estrone ([E1], estradiol [E2], plasma dehydroepiandrosterone-sulfate [DHEA-S], testosterone [T], dihydrotestosterone [DHT], delta 4-androstenedione [delta 4-A]), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin in postmenopausal patients with breast cancer randomly allocated to either AG treatment or bilateral surgical adrenalectomy as a control group. In response to either treatment, the plasma levels of E1 fell 62-75% (P less than 0.001) and urine E1 85.7-88.7% (P less than 0.001) in all study days over a 12-wk period. Similarly, the concentrations of E2 in plasma and urine fell 40-72% without statistically significant differences between the two treatment modalities. The relatively weak androgen, DHEA-S, was reduced by 92% (877.3 +/- 184.6 to 71.8 +/- 14.5 ng/ml) at 12 wk in women treated with AG, but suppressed nearly 99% (1,151 +/- 262 to 5.8 +/- 3.3 ng/ml) in adrenalectomized women. At all time points after treatment, the DHEA-S levels were significantly higher in patients receiving AG. Plasma concentrations of the potent androgens, T and DHT, were also relatively preserved during AG treatment. T levels were never significantly reduced by AG, and DHT concentrations were decreased only at the 4th wk to a maximum of 20%. delta 4-A levels fell 56% in response to this drug only on the 12th wk of therapy (basal, 0.79 +/- 0.09 ng/ml; 12 wk, 0.35 +/- 0.07 ng/ml). In marked contrast, all androgens fell significantly at each time period in response to surgical adrenalectomy, with an 81% maximum suppression of T, 73% of DHT, and 97% of delta 4-A. In response to estrogen suppression, plasma levels of FSH, LH, and prolactin did not change significantly throughout the treatment period in either therapy group. To examine possible contributions of the postmenopausal ovary to hormone levels during therapy, data from surgically castrate and spontaneously menopausal women were evaluated separately. No significant differences between the two groups were observed for E1, E2, T, DHT, DHEA-S, delta 4-A, LH, FSH, and prolactin. We conclude that equivalent and highly significant estrogen suppression occurs with either AG or surgical adrenalectomy although androgen secretion is preserved during AG treatment but not after surgical adrenalectomy. The combined effects of estrogen deprivation associated with androgen preservation might be significant in the therapeutic action of AG in hormone-responsive neoplasms.

Influence of the high-affinity growth hormone (GH)-binding protein on plasma profiles of free and bound GH and on the apparent half-life of GH. Modeling analysis and clinical applications.

The discovery of a specific high-affinity growth hormone (GH) binding protein (GH-BP) in plasma adds complexity to the dynamics of GH secretion and clearance. Intuitive predictions are that such a protein would damp sharp oscillations in GH concentrations otherwise caused by bursts of GH secretion into the blood volume, prolong the apparent half-life of circulating GH, and contribute a reservoir function. To test these implicit considerations, we formulated an explicit mathematical model of pulsatile GH secretion and clearance in the presence of absence of a specific high-affinity GH-BP. Simulation experiments revealed that the pulsatile mode of physiological GH secretion creates a highly dynamic (nonequilibrium) system, in which the half-life of free GH, its instantaneous secretion rate, and the GH-BP affinity and capacity all contribute to defining momentary levels of free, bound, and total GH, the percentage of GH bound to protein, and the percentage occupancy of GH-BP [corrected]. In contrast, the amount of free GH at equilibrium is specified only by the GH distribution volume and secretion rate and the half-life of free hormone. We conclude that the in vivo dynamics of GH secretion, trapping, and clearance from the circulation offer a variety of regulatory loci at which the time structure of free, bound, and total GH delivery to target tissues can be controlled physiologically.

Pituitary self-priming actions of gonadotropin-releasing hormone. Kinetics of estradiol's potentiating effects on gonadotropin-releasing hormone-facilitated luteinizing hormone and follicle-stimulating hormone release in healthy postmenopausal women.

We examined the kinetically distinct characteristics of estradiol's effects upon pituitary luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release in response to pulses of exogenous gonadotropin-releasing hormone (GnRH) in healthy postmenopausal individuals. The putative self-priming actions of GnRH on LH and FSH release were tested by intravenous injections of equal paired doses of GnRH (10 micrograms) before and after 1, 5, 10, and 30 d of pure estradiol-17 beta delivery via an intravaginal silastic ring. Self-priming actions of GnRH, as defined by heightened gonadotropin release in response to the second pulse of GnRH compared with the first, were completely absent in the hypoestrogenemic state. However, estradiol administration unmasked GnRH self-priming in a time-dependent fashion, with maximal expression after 5 and 10 d of steroid replacement, followed by attenuation by 30 d. Since estradiol's modulation of GnRH action was expressed differentially on LH and FSH release, we suggest that such facilitation of GnRH-stimulated pituitary LH and FSH release may provide an additional mechanism for dissociated secretion of gonadotropic hormones in health or disease.

Actions of estradiol on discrete attributes of the luteinizing hormone pulse signal in man. Studies in postmenopausal women treated with pure estradiol.

We assessed the time-dependent impact of estradiol on properties of the luteinizing hormone (LH) pulse signal in 12 hypoestrogenemic postmenopausal volunteers studied basally and after 1, 5, 10, and 30 d of estradiol delivery via an intravaginal Silastic ring. Computerized analysis of the plasma LH time series revealed a significant decrease in LH pulse frequency within 24 h of estrogen treatment, followed by a secondary increase (days 5 and 10), and then a sustained decline (day 30) in LH pulsatility. Estradiol also significantly suppressed incremental and maximal (but not fractional) LH pulse amplitudes in a biphasic manner. In contrast, LH peak duration was invariant until day 30 of estradiol replacement. These observations indicate that the well recognized biphasic actions of estradiol on mean serum LH concentrations can be modeled in relation to specific and time-dependent alterations in LH pulse frequency and amplitude.

Mechanisms subserving the trophic actions of insulin on ovarian cells. In vitro studies using swine granulosa cells.

Direct actions of insulin on gonadal tissues have been difficult to demonstrate in vivo. We have developed an in vitro system in which swine ovarian cells remain highly responsive to trophic actions of insulin. Purified porcine insulin significantly augmented the biosynthesis and secretion of progesterone by cultured granulosa cells. These stimulatory actions of insulin were dose- and time-dependent and saturable. Under serum-restricted conditions, insulin also significantly amplified the capacity of estradiol and 8-bromo cyclic AMP to stimulate progesterone production. Inhibitors of protein and RNA synthesis (cycloheximide, actinomycin D, and alpha-amanatin) inhibited insulin action. The stimulation of progesterone production by insulin was attributable to increased biosynthesis of pregnenolone, rather than diminished catabolism of progesterone to its principal metabolite, 20alpha-hydroxypregn-4-en-3-one. Insulin also enhanced progesterone production in the presence of a soluble sterol substrate, 5-cholesten-3beta,25-diol, which readily gains access to the mitochondrial cholesterol side-chain cleavage system. Moreover, exposure of granulosa cells to insulin produced a three- to sevenfold increase in mitochondrial content of cytochrome P-450 measured by difference spectroscopy, with a corresponding increase in mitochondrial cholesterol side-chain cleavage activity. The capacity of insulin to facilitate progesterone biosynthesis by ovarian cells was mimicked by the insulinlike somatomedin, multiplication stimulating activity, but not by epidermal growth factor, fibroblast growth factor, or porcine relaxin. Insulin's augmentation of progesterone production reflected a selective action on progestin biosynthesis, since insulin significantly suppressed estrogen biosynthesis by granulosa cells.Thus, our investigations indicate that insulin acts on ovarian cells selectively to stimulate pregnenolone (but not estrogen) biosynthesis. The actions of insulin are exerted by processes that require protein and RNA synthesis, and by mechanisms that augment mitochondrial cytochrome P-450 content and facilitate the utilization of cholesterol in the side-chain cleavage reaction. The striking mimicry of insulin effect by multiplication stimulating activity suggests that insulin action may be mediated through somatomedin receptors. Moreover, in view of the high concentrations of somatomedin in ovarian follicles in vivo, our in vitro observations suggest that specific trophic actions of insulin or insulinlike growth factors are likely to significantly regulate the differentiated function of the Graafian follicle in vivo.