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

Bright ligand-activatable fluorescent protein for high-quality multicolor live-cell super-resolution microscopy

We introduce UnaG as a green-to-dark photoswitching fluorescent protein capable of high-quality super-resolution imaging with photon numbers equivalent to the brightest photoswitchable red protein. UnaG only fluoresces upon binding of a fluorogenic metabolite, bilirubin, enabling UV-free reversible photoswitching with easily controllable kinetics and low background under Epi illumination. The on- and off-switching rates are controlled by the concentration of the ligand and the excitation light intensity, respectively, where the dissolved oxygen also promotes the off-switching. The photo-oxidation reaction mechanism of bilirubin in UnaG suggests that the lack of ligand-protein covalent bond allows the oxidized ligand to detach from the protein, emptying the binding cavity for rebinding to a fresh ligand molecule. We demonstrate super-resolution single-molecule localization imaging of various subcellular structures genetically encoded with UnaG, which enables facile labeling and simultaneous multicolor imaging of live cells. UnaG has the promise of becoming a default protein for high-performance super-resolution imaging.

Photoconvertible proteins occupy two color channels thereby limiting multicolour localisation microscopy applications. Here the authors present UnaG, a new green-to-dark photoswitching fluorescent protein for super-resolution imaging, whose activation is based on a noncovalent binding with bilirubin.

Effect of opioid antagonists on sex hormone secretion

BACKGROUND

Endogenous opioids have roles in various functions in different parts of the body, including intestinal motility, suppression of pain, reinforcement of behavior, and regulation of the hypothalamic-pituitary-gonadal axis. The endogenous opioid system is also recognized to be involved in the negative-feedback regulation of the release of LH and testosterone.

AIM

The reviewed articles herein show the development of the current model of this regulation, the evidence supporting it, and also the observed effects of opioid antagonist (naloxone, naltrexone, and nalmefene) on the system.

MATERIALS AND METHODS

Review of the studies published during the years 1979-1996 (no significant studies made after that). Search from databases Pubmed, SciFinder, and Medline with search words opioid antagonists, hormones, LH, testosterone, and GnRH, in different combinations.

RESULTS/CONCLUSIONS

Opioid antagonists seem to increase the secretion of GnRH in the hypothalamus which then causes a pulsatile release of LH in the pituitary and secretion of testosterone. According to the experiments, the frequency of pulses and concentration of LH and testosterone in plasma seem to increase. These effects are seen in both men and women (at early follicular phase). More research is needed to investigate the consequences of these effects in general.

Opioid and cocaine combined effect on cocaine-induced changes in HPA and HPG axes hormones in men

Nalbuphine, a mixed micro-/kappa-opioid analgesic, may have potential as a new medication for the treatment of cocaine abuse. Kappa-opioid agonists functionally antagonize some abuse-related and locomotor effects of cocaine, and both kappa-selective and mixed micro-/kappa-opioids reduce cocaine self-administration by rhesus monkeys. Because cocaine's interactions with the hypothalamic-pituitary-adrenal and (HPA) hypothalamic-pituitary-gonadal (HPG) axes may contribute to its reinforcing properties, we examined the effects of cocaine alone and in combination with nalbuphine. Neuroendocrine effects of a single dose of cocaine alone (0.2 mg/kg, IV), with nalbuphine (5 mg/70 kg, IV)+cocaine (0.2 mg/kg, IV) in combination were compared in seven adult men (ages 18-35) who met DSM-IV criteria for current cocaine abuse. Cocaine alone, and in combination with nalbuphine was administered on separate test days under placebo-controlled, double blind conditions. Cocaine stimulated ACTH, cortisol, and LH, whereas cocaine+nalbuphine in combination produced a smaller increase in ACTH, and decreased cortisol and LH. Thus it appears that nalbuphine attenuated cocaine's effects on ACTH, cortisol, and LH. These data are consistent with our earlier report that nalbuphine modestly attenuated cocaine's positive subjective effects, and that the subjective and cardiovascular effects of cocaine+nalbuphine in combination were not additive.

Indirect androgen doping by oestrogen blockade in sports

Androgens can increase muscular mass and strength and remain the most frequently abused and widely available drugs used in sports doping. Banning the administration of natural or synthetic androgens has led to a variety of strategies to circumvent the ban of the most effective ergogenic agents for power sports. Among these, a variety of indirect androgen doping strategies aiming to produce a sustained rise in endogenous testosterone have been utilized. These include oestrogen blockade by drugs that act as oestrogen receptor antagonists (antioestrogen) or aromatase inhibitors. The physiological and pharmacological basis for the effects of oestrogen blockade in men, but not women, are reviewed.

Heritability of reproductive hormones in adult male twins

BACKGROUND

Proper functioning of the male reproductive axis depends on complex feedback systems between several hormones. In this study, the genetic contribution of various endocrine components of the hypothalamic-pituitary-testicular axis is evaluated and previously observed differences in FSH and inhibin B levels between mono- (MZ) and dizygotic (DZ) twins are re-investigated.

METHODS

Inhibin B, FSH, LH, sex hormone-binding globulin (SHBG) and testosterone levels were assayed in 128 adult males (20 MZ twin pairs, 7 single MZ twins, 10 DZ twin pairs, 27 single DZ twins and 34 siblings of twins, constituting 10 sibling pairs), aged 15.6-68.7 years. Hormone levels were compared across zygosity groups and heritability estimates were obtained using maximum likelihood variance component analysis.

RESULTS

Heritability estimates ranged from 56% (testosterone) to 81% (inhibin B and SHBG). For LH and FSH, the heritability was estimated at 68% and 80% respectively. No mean differences in hormone levels were observed across groups.

CONCLUSIONS

All measured hormones are highly heritable. A difference in the FSH-inhibin B feedback system between DZ twin males and MZ twin males could not be confirmed.

Interictal EEG discharges, reproductive hormones, and menstrual disorders in epilepsy

We evaluated reproductive endocrine function in women with unilateral temporolimbic epilepsy and normal control subjects to assess the effects of epilepsy, epilepsy laterality, and antiepileptic drug use on the cerebral regulation of hormonal secretion. The findings indicate that reproductive endocrine function differs between women with epilepsy and normal control subjects. Significant differences exist at all levels of the reproductive neuroendocrine axis, that is, hypothalamus, pituitary, and peripheral gland. Differences show significant relationships to the epilepsy itself as well as to medication use. Reproductive neuroendocrine changes occur in a stochastic manner such that the laterality of unilateral temporolimbic discharges is associated with predictable directional changes in hormonal secretion at all levels of the reproductive neuroendocrine axis. These directional changes are consistent with the finding that different reproductive disorders may develop in relation to left- and right-sided temporolimbic epilepsy. Hormonal changes can show close temporal relationship to the occurrence of interictal epileptiform discharges and may vary in relation to the laterality of the discharges. Antiepileptic drugs differ in their effects on reproductive hormone levels. There are notable differences between enzyme-inducing and noninducing drugs. Menstrual disorders are more common among women with interictal discharges as well as women with abnormal hormonal findings.

Androgens and the ageing male and female

Androgens play a number of important physiological roles in the human. In the male, testosterone is required for virilization, normal sexual function, and both stimulation and maintenance of bone and muscle mass. Epidemiological studies have shown a progressive decline in testosterone levels with ageing in men. The clinical significance of this decline is still unclear, and there is controversy as to whether a specific syndrome of androgen deficiency or 'andropause' exists. The benefits of testosterone supplementation in this age group have yet to be equivocally established, and long-term safety data on testosterone administration in this setting are lacking. In the female, a decline in testosterone levels with ageing has been less clearly established due, at least in part, to the absence of sensitive assays. Available data suggest that the major role of testosterone replacement after menopause may be in those women who have had an oophorectomy.

Endocrine regulation of gonadotropin glycosylation

The pituitary gonadotropins--luteinizing hormone and follicle-stimulating hormone--as well as the placental choriogonadotropin belong to the family of glycoprotein hormones. These structurally related hormones, which regulate several major reproductive functions of the body, are heterodimers consisting of a common alpha-subunit noncovalently bound to a beta-subunit. The N- and O-linked oligosaccharide chains of these gonadotropins play an important role in intracellular folding, assembly, secretion, metabolic clearance, and biological activity of the hormone. Gonadotropin glycosylation is a highly complex process; within the gonadotropes it is modulated by a variety of extrapituitary factors of hypothalamic and gonadal origin. In particular, estrogens and androgens appear to regulate terminal sialylation and/or sulfation of the oligosaccharide attachments and hence some functional properties of the gonadotropin molecule determined by these residues, i.e., metabolic clearance and in vivo biopotency. Through these extrapituitary inputs, the anterior pituitary may not only regulate the quantity but also the quality of the gonadotropin signal delivered to the gonads in a given physiologic or pathologic condition.

Acute and long-term effects of AIDS and injection drug use on gonadal function

Hypogonadism has been observed in both the HIV-infected population and injection drug users (IDUs). Considering these populations in conjunction is essential because IDUs and HIV often occur in the same individual. Additionally, although the etiology of hypogonadism may be different in each population, its treatment with respect to the underlying condition is similar. The philosophy of both AIDS and IDU treatment has changed drastically in recent years, due to several factors. Survival rates of HIV patients have been steadily increasing, forcing a closer examination of the long-term effects of AIDS-related symptoms, and the quality of life issues associated therewith. In comparison, IDU is now viewed as a chronic addiction like that for alcoholism, which must be treated, rather than an untreatable personal problem. Therefore, it is logical that the endocrine and metabolic changes associated with both HIV and IDU should be examined to help alleviate these symptoms in a continuing effort to treat the underlying condition.

Acute effects of nalmefene on LH, prolactin, and testosterone in male rhesus monkeys

The effects of the long-acting opioid antagonist, nalmefene [17-N-cyclopropylmethyl-3,14-beta-dihydroxy-4, 5-alpha-epoxy-6-methylene morphinan hydrochloride] on LH, T, and prolactin release in rhesus monkeys are unknown. The acute effects of nalmefene (0.01 and 0.10 mg/kg, IV) or placebo on LH, PRL, and T were studied, and samples were collected at 10-min intervals for 360 min to permit cluster analysis of pulsatile release patterns. LH increased significantly within 30 min after nalmefene, and remained significantly above baseline levels for 50 to 60 min (p < 0.05). Testosterone increased significantly within 70 to 80 min after nalmefene, and remained significantly above baseline for 60 min (p < 0.05). Although nalmefene antagonizes opioid agonists for 6-8 h, inhibitory feedback by testosterone appeared to limit the duration of its antagonism of endogenous opioid inhibition of LHRH and stimulation of LH. Nalmefene did not change LH or PRL pulse frequency or amplitude significantly in comparison to placebo administration.

Effect of naloxone on serum testosterone in adult male rabbits

Considerable evidence suggests that endogenous opioids may play an important role in the hypothalamic LH-releasing hormone. Administration of high doses of naloxone, an opiate antagonist, produces an increase in plasma concentration of LH. Naltrexone administration to healthy males produces an increase in both immunoactive and bioactive LH. The objective of the present work was to assess the effect of low doses of naloxone during 10 consecutive days on testosterone serum levels in rabbit. Three groups of five rabbits were injected with naloxone or saline. Naloxone was tested at 0.1 and 0.01 mg/kg day-1. Blood samples were taken at 90 min and 1, 2, 4, 7, 10, and 14 days after starting naloxone administration. Plasma testosterone (T) levels were measured by RIA. T levels increased progressively through the study in the experimental groups. The differences were significant after days 4 and 7 for 0.01-mg/kg and 0.1-mg/kg doses, respectively. T levels in both groups peaked at day 10 and decreased at day 14 (4 days after treatment).

Neuroendocrine mechanisms mediating awakening of the human gonadotropic axis in puberty

The hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator presides over the pulsatile and feedback-regulated activities of the pituitary-gonadal axis. Awakening of synchronous activity of the GnRH neuronal ensemble in the earliest stages of puberty heralds the onset of full activation of the reproductive axis in girls and boys. Progression from prepuberty to adulthood in boys is directed by marked (30-fold) amplitude enhancement of pulsatile luteinizing hormone (LH) secretion, as assessed by an ultrasensitive immunofluorometric assay and deconvolution analysis. There is a much less apparent rise in LH secretory burst frequency (approximately 1.3-fold increase). Consequently, human puberty is an amplitude-driven neuroendocrine maturational process. However, less is known about pulsatile follicle-stimulating hormone (FSH) release in puberty. Multiple pathophysiologies that result in hypogonadotropic hypogonadism can converge on a final common mechanism of attenuated hypothalamic GnRH pulse generator output and hence reduced LH (and FSH) secretion. Disturbances may take the form of reduced GnRH pulse frequency and/or attenuated GnRH secretory burst mass. When the pathophysiology of hypogonadism originates exclusively in a failed GnRH pulse generator, then either treatment of the primary disease process where possible (e.g., by refeeding in starvation, improved metabolic control in diabetes mellitus, dopamine agonist treatment in hyperprolactinemia, etc) and/or treatment with pulsatile GnRH (e.g., in Kallmann's syndrome, isolated hypothalamic lesions, etc.) can provide relevant therapeutic options in children and adults.

Role of the hypothalamic opioidergic system in the control of gonadotropin secretion in elderly men

The role of opioidergic system in controlling gonadotropin secretion in elderly men still remains uncertain. In the present study, we attempted to examine the opioidergic inhibitory tone imposed on GnRH release mechanism in elderly men by monitoring the plasma gonadotropin response to the opiate receptor antagonist naloxone hydrochloride. Six normal young men and 10 elderly men with no endocrinological diseases volunteered for the present study. In young men, plasma LH showed a biphasic increase in response to naloxone and plasma LH level during naloxone treatment was significantly higher than the mean of prenaloxone control levels. In contrast, plasma LH in elderly men was not affected by naloxone. The ratio of the peak plasma LH response during naloxone treatment to the mean pre treatment LH level (plasma peak/basal LH ratio) declined with the advance of age (r = -0.74, P < 0.005) and also correlated significantly with plasma free testosterone level (r = 0.45, P < 0.05). These data suggest (1) that the hypothalamic opioidergic tone is reduced in elderly men and (2) that the primary testicular insufficiency with the advance of age may play a major role in the decline of the hypothalamic opioidergic tone in elderly men.

A review of hormonal findings in cluster headache. Evidence for hypothalamic involvement

The cause of cluster headache remains to be determined. The involvement of peripheral neurovascular structures can explain the pain and autonomic signs of a cluster attack, but not its rhythmicity. The central theory of cluster headache attributes the cyclic recurrence to involvement of the hypothalamus. To evaluate hypothalamic dysfunction a number of hormone studies have been carried out on cluster headache patients. Alterations in plasma melatonin, cortisol, testosterone, gonadotrophins, prolactin, growth hormone and thyrotropin have been documented, some only in the cluster period but others in the remission phase of the illness. We believe that the hormonal abnormalities in cluster headache support disorders of hypothalamic function.

Effects of opioid receptor blockade on luteinizing hormone (LH) pulses and interpulse LH concentrations in normal women during the early phase of the menstrual cycle

To determine the role of endogenous opioid peptides in regulating pulsatile luteinizing hormone (LH) release in the early follicular phase of the menstrual cycle of eumenorrheic women, we evaluated serum LH concentrations in blood collected every 10 min for 12 h in 27 women each studied during two menstrual cycles: (1) without pretreatment and (2) following oral administration of naltrexone, a mu opiate receptor blocking agent, at a dose of 1.0 mg/kg. Pulsatile LH release was assessed by the CLUSTER algorithm. The mean (+/- SE) integrated serum LH concentration (IU/L/min) increased following the administration of naltrexone (4715 +/- 298) in comparison to the control day (3997 +/- 381; p = 0.0008). The mean number of LH pulses (/12 h) detected on the naltrexone day (10.3 +/- 0.3) was higher than on the control day (8.9 +/- 0.4; p = 0.0068). Mean maximal LH peak height (IU/L) was greater on the naltrexone (7.8 +/- 0.5) vs control (6.7 +/- 0.5) days (p = 0.0064) as was the interpulse valley mean serum LH concentration (IU/L; 6.3 +/- 0.4 vs 5.0 +/- 0.4; p = 0.0013). No difference was noted in the mean incremental LH pulse amplitude (IU/L; 1.9 +/- 0.1 vs 2.1 +/- 0.1; p = 0.13), or peak duration (min; 40 +/- 1.8 vs 45.0 +/- 2.4; p = 0.06). Mean LH peak area (IU/L/min) was greater on the control (45.0 +/- 2.4) vs naltrexone (40 +/- 1.8) days (p = 0.0475).(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical features and circulating gonadotropin, insulin, and androgen interactions in women with polycystic ovarian disease

OBJECTIVE

To investigate the interactions of hyperinsulinemia and inappropriate gonadotropin secretion in women with polycystic ovarian disease (PCOD).

DESIGN

Comparative study of endocrinologic parameters in subjects with PCOD.

SETTING

Open patient clinic of reproductive endocrinology at University Central Hospital of Turku, Finland.

PATIENTS

Fourteen nonobese and 10 obese patients with PCOD. Seven healthy women for reference data collection. Normal thyroid function, serum prolactin concentration, normal diurnal cortisol variation, euglycemia in all subjects.

MAIN OUTCOME MEASURES

Serum concentrations of insulin, testosterone, androstenedione, dehydroepiandrosterone sulfate, sex hormone-binding globulin, immunoreactive luteinizing hormone (LH), bioactive LH, and follicle-stimulating hormone (FSH).

RESULTS

The concentration of insulin was higher and that of bioactive LH was lower in obese than in nonobese PCOD women in whom the levels were also above the upper reference value. There was a negative correlation between insulin and bioactive LH levels (r = -0.57). Bioactive LH correlated inversely with the body mass index (BMI) (r = -0.50). After eliminating the effect of the BMI, the correlation between bioactive LH and insulin was no longer significant (r = -0.37). The bioactive LH and immunoreactive LH/FSH ratio correlated significantly (r = 0.68).

CONCLUSIONS

These data demonstrate that hyperandrogenic women can be divided into two subgroups: those with insulin resistance, normal or minimally elevated LH, and markedly elevated insulin levels; and those with elevated LH levels, no insulin resistance, and normal insulin concentrations. Obesity is associated with the former, and high bioactive LH levels with the latter subgroup.

Neuroendocrine regulation of pulsatile luteinizing hormone secretion in elderly men

Leydig cell function is driven by LH, secreted in a pulsatile manner by the anterior pituitary in response to episodic discharge of hypothalamic LHRH into the pituitary portal circulation, under control of a yet to be defined neural mechanism, the "hypothalamic LHRH pulse generator". The normal aging process in elderly men is accompanied by a decline in Leydig cell function. Whereas primary testicular factors undoubtedly play an important role in the decrease of circulating (free) testosterone levels with age, recent studies demonstrated that aging also affects the central compartment of the neuroendocrine cascade. Hypothalamic alterations comprise changes in the regulation of the frequency of the LHRH pulse generator with an inappropriately low frequency relative to the prevailing androgen impregnation and opioid tone, and with an increased sensitivity to retardation of the LHRH pulse generator by androgens. As observed by some authors in basal conditions and by others after endocrine manipulations. LH pulse amplitude seems also to be reduced in elderly men as compared to young subjects. This is most probably the consequence of a reduction in the amount of LHRH released by the hypothalamus. Indeed, challenge of the gonadotropes with low, close to physiological doses of LHRH in young and elderly men reveals no alterations in pituitary responsiveness when looking at either the response for immunoreactive LH or bioactive LH. Deconvolution analysis on data obtained after low-dose LHRH suggests a markedly prolonged plasma half-life of LH in elderly men, a finding which may explain the paradoxical increase of mean LH levels in face of the reduced or unchanged frequency and amplitude of LH pulses.

Physical exercise and menstrual cycle alterations. What are the mechanisms?

The prevalence of menstrual cycle alterations in athletes is considerably higher than in sedentary controls. There appears to be a multicausal aetiology, which makes it extremely difficult to dissociate the effects of physical exercise on the menstrual cycle from the other predisposing factors. From cross-sectional studies it appeared that physical training eventually might lead to shortening of the luteal phase and secondary amenorrhoea. Prospective studies in both trained and previously untrained women have shown that the amount and/or the intensity of exercise has to exceed a certain limit in order to elicit this phenomenon. We hypothesise, therefore, that apart from a certain predisposition, athletes with a training-induced altered menstrual cycle are overreached (short term overtraining, which is reversible in days to weeks after training reduction). Menstrual cycle alterations are most likely caused by subtle changes in the episodic secretion pattern of luteinising hormone (LH) as have been found in sedentary women with hypothalamic amenorrhoea as well as in athletes after very demanding training. The altered LH secretion then, might be caused by an increased corticotrophin-releasing hormone (CRH) secretion which inhibits the gonadotrophin-releasing hormone (GnRH) release. In addition, increased CRH tone will lead to increased beta-endorphin levels which will also inhibit the GnRH signaller. Finally, the continuous activation of the adrenals will result in a higher catecholamine production, which may be converted to catecholestrogens. These compounds are known to be potent inhibitors of GnRH secretion. In conclusion, menstrual cycle alterations are likely to occur after very demanding training, which causes an increase secretion of antireproductive hormones. These hormones can inhibit the normal pulsatile secretion pattern of the gonadotrophins.

Relationship between cerebrospinal fluid beta-endorphin and plasma pituitary-gonadal hormone levels in women

Brain beta-endorphin (beta-EP) plays an important role in regulating the hypothalamus-pituitary-gonadal axis activity. Cerebrospinal fluid (CSF) beta-EP levels seem to reflect the central rather than pituitary secretion. With the aim to correlate the changes of plasma estradiol (E2), progesterone, luteinizing hormone (LH) and follicle-stimulating hormone with brain beta-EP, CSF levels of beta-EP were measured in 15 normally cycling and 15 postmenopausal women. CSF beta-EP levels in post-menopausal women were lower than in fertile women. A positive correlation between plasma E2 and CSF beta-EP level was found in all women. In fertile women CSF beta-EP levels were inversely correlated to plasma gonadotropin levels. These results showed that CSF beta-EP levels differ between fertile and postmenopausal women and are correlated with plasma LH and E2, suggesting a strong linkage between central beta-EP levels and pituitary-gonadal axis hormones.

Endocrine aspects of postnatal mental disorders

Biological research in postnatal mental illness has only a short history and few encouraging data have yet emerged. The most promising positive findings are perhaps preliminary evidence for an increase of postnatal depression in women with postpartum thyroid dysfunction, some evidence for an enhanced sensitivity to changes in progesterone levels in postnatal depression, and the presence of an opioid peptide with unknown function in the cerebrospinal fluid of women with puerperal psychosis. Although steroid hormones are generally thought to be aetiologically relevant since they freely enter the brain and are known to interact with central monoamine neurotransmitter systems, attempts to demonstrate abnormal levels in postnatal disorders have been disappointing. An important reason for this outcome may be the usually employed approach of isolated hormone measurements. Ovarian steroid levels show marked interindividual variations. Thus significant between-group differences may only be obtained when large numbers of subjects are tested. Since only the unbound fraction can enter the brain, its measurement should be included in such studies. In the case of cortisol, single values are insufficient because of the pulsatile nature and the circadian pattern of its release. Thus serial sampling over 24 hours is more appropriate to detect secretory abnormalities. Measurements of circulating peptides are difficult to interpret since the amount reaching the brain is at best small. What is needed here are estimations of peptides in the cerebrospinal fluid which, however, pose ethical problems. Another explanation for the dearth of consistent positive data may be that women with postnatal mental disorders react to normal postnatal changes differently to women who remain well after childbirth. There is already evidence that patients at high risk of puerperal manic-depressive illness develop a hypersensitivity of central D2 receptors which may be related to the effects of oestrogen withdrawal on the function of DA systems. Further investigations of central neurotransmitter function are needed. In many ways postnatal mental disorders provide a unique opportunity for psychosomatic research since their onset can almost be predicted and follows an event which is associated with changes in many physiological systems. Results of recent neuropharmacological and behavioural investigations into the central effects of steroid and peptide hormones provide the basis for a multitude of pathogenetic hypotheses to be tested in postnatal mental disorders and research in this area may see exciting times ahead.

Opioid control of luteinizing hormone secretion in humans

The observation that heroin-addicted subjects are amenorrheic and/or hypogonadic suggested a possible role of endogenous opioid peptides (EOP) in the regulation of the hypothalamus-pituitary-gonodal axis. Because EOP are localized all through the axis, they may influence the reproductive function acting at various levels. The injection of morphine decreases plasma LH levels, abolishing the pulsatile pattern of secretion. The evidence that naloxone, an opiate receptor blockade, increases LH levels suggests a tonic inhibitory action of EOP. The naloxone-induced LH increase is not observed before pubertal maturation, in both sexes, and is absent in children with delayed or precocious puberty and in those with Klinefelter's or Turner's syndrome, suggesting a role of gonadal function on the opioid control of LH secretion. In adult women this LH response to naloxone is present during the periovulatory and the luteal phase of the menstrual cycle, suggesting a permissive role of estradiol and mainly of progesterone on the action of EOP on the LH secretion. Indeed, in amenorrheic subjects naloxone lacks to stimulate plasma LH levels and the treatment for the induction of ovulation restores this activity. An increased inhibitory action of EOP on GnRH release may explain the inefficacy of naloxone to stimulate LH secretion in hypogonadotropinic patients, while a decreased action has been hypothesized in postmenopausal women. The clinical implications of EOP in reproductive medicine appear to be promising.

Pathophysiological features of the pulsatile secretion of biologically active luteinizing hormone in man

The development of an in vitro bioassay of high specificity, sensitivity and precision for the measurement of low circulating concentrations of biologically active glycoprotein hormones has offered exciting new insights into the in vivo secretion and metabolic clearance of luteinizing hormone (LH) in various pathophysiological states. Moreover, the most recent combined application of the rat interstitial cell testosterone (RICT) bioassay and a novel multiple-parameter deonvolution model has allowed investigators to dissect plasma concentration profiles of bioactive LH into defined secretory bursts, which have numerically explicit amplitudes, locations in time, and durations, and are acted upon by determinable subject- and study-specific endogenous metabolic clearance rates. Here, we have: (i) reviewed the ability of the endogenous GnRH pulse signal to regulate the in vivo secretion of biologically active LH molecules as assessed in the RICT and by deconvolution mechanics; (ii) demonstrated that low-dose exogenous GnRH pulses effectively mimic spontaneous bioactive LH pulsatility; (iii) investigated the role of endogenous androgen and estrogen in modulating bioactive gonadotropin secretion in men and women; and (iv) described significant alterations in endogenous LH bioactivity in puberty and healthy aging.

Quantitative and qualitative changes in LH secretion following pulsatile GnRH therapy in a man with idiopathic hypogonadotrophic hypogonadism

The pattern of bioactive and immunoreactive LH secretion before and during pulsatile GnRH therapy (18 micrograms/90 min) in a hypogonadotrophic hypogonadal male has been studied. Before treatment the patient was azoospermic and had low testosterone (1.2 nmol/l) with low and apulsatile immunoreactive LH (1.9 +/- 0.2 IU/l) and FSH (1.4 +/- 1.9 IU/l) levels. There was no detectable LH bioactivity. During the first 24 h of GnRH therapy there was a small increase in immunoreactive (5.4 +/- 0.8 IU/l) and bioactive (6.7 +/- 1.3 IU/l) LH, with an irregular pattern and little effect on testosterone production (2.2 nmol/l). Within 1 week of treatment both bioactive (30.5 +/- 6.8 IU/l) and immunoreactive (13.6 +/- 1.5 IU/l) LH levels were above the normal range and the pattern of secretion was pulsatile. The bioactive to immunoreactive (B:I) LH ratios within the pulses (2.6 +/- 0.3) were higher (P less than 0.01) than between pulses (1.97 +/- 0.1) and the testosterone concentration (17.8 +/- 2.1 nmol/l) was now normal. At one month LH secretion was similar and testosterone pulses of high amplitude were evident corresponding to high-amplitude bioactive LH pulses. By 3 months mature spermatozoa (1.3 x 10(6)/ml) were seen in the patient's semen. The pattern of LH secretion was pulsatile but the levels of bioactive (13.1 +/- 3.6 IU/l) and immunoreactive (9.5 +/- 1.3 IU/l) LH decreased towards the normal range reflecting maturation of the testicular feedback control at the pituitary level. This effect was more pronounced on bioactive rather than immunoreactive LH secretion (57% vs 32% relative decrease). At 6 months LH levels were similar and the sperm count was normal (34 x 10(6)/ml).

Neuroendocrine control of male reproductive function. The opioid system as a model of control at multiple sites

It is known that the same peptide can be identified in different secretory tissues and in the central nervous system (CNS). We now provide evidence that the same peptides can be found in different organs related to the control of a single function, and speculate on the possibility that this reflects a common neuroendocrine programming. Endogenous opioid peptides (EOP) inhibit the reproductive function acting via the CNS. EOP inhibit gonadotropin secretion in rodents and humans via inhibition of GnRH release and have direct inhibitory actions at the pituitary level via specific binding sites on the gonadotrophs. However, EOP can also be synthesized in the testis and in different compartments of the male genital tract. Several findings indicate that EOP of the reproductive tract have a local, paracrine role. These include: (1) the detection of significant beta-endorphin (beta-EP) production by rat Leydig cells (Lc) in cultures; (2) the hormonal regulation of Lc beta-EP production by positive (gonadotropins) and negative (steroids, glucocorticoids, GnRH) factors; (3) the presence of opioid binding sites (Kd in the nanomolar range) in tubular homogenates and Sertoli cells (Sc) in culture of adult and immature rat testes; (4) the inhibition of basal and FSH-stimulated ABP production by Sc in culture when chronically exposed to beta-EP treatment; (5) the detection of high levels of beta-EP and met-enkephalin in human semen with values 6-12 times higher than in plasma; (6) the evidence for inhibitory functions of seminal opioids on sperm motility, vas deferens muscle contraction and partner immune system. Thus the same peptides, i.e. EOP, may control the reproductive function at multiple sites, operating as a multimessenger system in which the central and peripheral level are unified by the common chemical and inhibitory nature of the message.

Endorphins in male impotence: evidence for naltrexone stimulation of erectile activity in patient therapy

In the present study we evaluated whether naltrexone administration could stimulate sexual function in 30 male patients, ages 25 to 50 years, with idiopathic impotence of at least one year's duration and not of organic etiology. The patients received naltrexone (50 mg/day) or placebo, on a random basis for two weeks. Sexual performance, expressed as the number of full coitus/week, was assessed before (time 0) and during (on days 7 and 15) each treatment. The naltrexone therapy significantly increased the number of successful coitus compared to placebo after 7 and 15 days of treatment: improvement of sexual performance was evident in 11 out of the 15 treated patients. All the patients experienced a significant increase in morning and spontaneous full penile erections/week. No significant side effects were reported. Endocrine studies revealed no significant modification of plasma LH, FSH or testosterone by naltrexone, suggesting that the positive effect of the drug on sexual behavior was exerted at a central level. A two-month follow-up, at which time patients were off treatment, erectile capacity had returned to baseline in 10 patients, while five reported complete recovery of their sexual ability. We hypothesize that an alteration in central opioid tone is present in idiopathic impotence and is involved in the impairment of sexual behavior.

Bioactive LH in women with polycystic ovaries and the effect of gonadotrophin suppression

Discrepancies between levels of bioactive LH (B-LH) and immunoreactive LH (I-LH) in polycystic ovarian syndrome (PCO) have been reported previously. Serum levels of I-LH, B-LH (by dispersed Leydig cell assay), FSH, oestradiol (E2) and progesterone (Prog) were measured once to three times weekly over 4 weeks in 13 women with classical clinical, ultrasound and endocrine features of PCO. Eleven women attending for infertility but whose profiles when studied three times weekly by combined endocrine and ultrasound assessment were normal and ovulatory served as controls. Seven of the women with PCO were evaluated during and after 3 weeks suppression with ethinyloestradiol (30 micrograms) plus 150 micrograms either of desogestrel or levonorgestrel; two were given both treatments. Both I-LH and B-LH levels were higher in PCO patients (20 +/- SD 5 U/l and 46 +/- 9 U/l respectively, P less than 0.0001), compared with all phases of the normal cycles except the mid-cycle peak. The B-LH to I-LH (B:I LH) ratio in PCO patients (2.5 +/- 0.7) was higher than in all the control cycle phases (P less than 0.05). I-LH, B-LH, B:I LH ratio, FSH and E2 were all suppressed from the second week of oestrogen-progestogen treatment (P less than 0.01) and returned gradually to pretreatment levels by the third or fourth week after suppression. The LH and FSH levels and B:I LH ratio in PCO patients during suppression were comparable with levels in the early and mid-follicular phases of control cycles but the LH/FSH ratio remained significantly raised (P less than 0.01) at 2.3 +/- 0.7.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the responsiveness of luteinizing hormone secretion to infusion of the opioid antagonist naloxone throughout male sexual maturation

The present study investigated the time of male sexual maturation during which hypothalamic inhibitory opioid activity can be detected. Normal prepubertal (Tanner stage G 1 (Ts-G1) (n = 4], early pubertal (Ts-G2 (n = 5], pubertal (Ts-G3 (n = 4), and Ts-G4 (n = 2] and adult subjects (Ts-G5 (n = 4] receives a rapid infusion of the selective opiate antagonist nalocone (NAL) (20 mg over 10 min). LH secretion was assessed by frequent (every 10 min for 2 h) venous sampling before and after administration of the opiate blocker, as well as by the LH response to exogenous GnRH. All but one (a Ts-G2 subject) pubertal boys showed aprompt and sustained increase in serum LH concentrations after NAL administration, as disclosed by the areas under the LH curve (aLHc) calculated from samples obtained before and after NAL infusion (aLHc in four Ts-G2 responders, 162 +/- 20 (mean +/- SEM) vs 314 +/- 56 mIU/ml/min before and after NAL respectively, P less than 0.025; Ts-G3, 227 +/- 35 vs 362 +/- 56 mIU/ml/min, P less than 0.025; Ts-G4 and Ts-G5, 432 +/- 77 vs 687 +/- 91 mIU/ml/min, P less than 0.05). In contrast, none of the prepubertal children had significant changes in LH secretion after the NAL challenge (154 +/- 17 vs 154 +/- 9 mIU/ml/min). Although all NAL responders exhibited serum testosterone (T) levels above 5 nmol/l, a positive correlation between individual T values and magnitude of LH responses to NAL was not found. All subjects had significant serum LH increments after GnRH administration. In a second series of studies, additional groups of Ts-G1 subjects were primed during 5 days either with GnRH alone or with GnRH plus sex steroids (ethinyl oestradiol 12.5 micrograms/12 h or testosterone enanthate 1.8 mg/kg body weight (single dose], before NAL administration, to investigate whether hypothalamic opioid activity might be unmasked by additional sex steroids. None of the priming schemes significantly modified the pituitary LH responses to NAL infusion (GnRH-primed group, 145 +/- 48 vs 139 +/- 43 mIU/ml/min before and after NAL, respectively; GnRH plus ethinyl oestradiol-primed group, 124 +/- 42 vs 107 +/- 34 mIU/ml/min; GnRH plus testosterone enanthate-primed group, 64 +/- 10 vs 57 +/- 24 mIU/ml/min). This study suggests that the development and/or maturation of the opioid control of LH secretion is temporally related with the onset of puberty.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

The effect of long-term opiate antagonist administration to pubertal boys

To test further the hypothesis that opiatergic pathways controlling gonadotropin production may be functional during early to mid adolescence, nine pubertal boys with bone ages ranging from 10 to 15 were given the long-acting opiate antagonist, naltrexone, for up to 4 weeks. Urinary gonadotropin measurements were assessed before, during, and after drug administration. In three early to mid-pubertal boys who received naltrexone for 3 to 4 weeks, LRH testing was also performed. No evidence of a stimulatory FSH or LH response to naltrexone was found in any of the patients evaluated. The data do not support the operation of an opiate-mediated mechanism in the control of pubertal onset in man.

Neuroendocrine control processes. Pubertal onset and progression

This discussion has outlined current concepts in neuroendocrinologic control of pubertal onset and progression. Central nervous system regulation of the arcuate nucleus (ventromedial hypothalamus) pulse generator that subsequently controls pituitary gonadotropin synthesis and secretion has been highlighted. Significant investigative issues that deserve assessment in the next several years include the following: 1. Systematic neuropharmacologic, electrophysiologic, and anatomic assessment of the hypothalamic arcuate nucleus. These assessments would include the use of recombinant DNA technology to probe cellular regulation of GnRH production. 2. Physiologically oriented examination of hypothalamic GnRH synthesis and secretion, along with function in the remaining reproductive endocrine system, during situations of nutritional impairment and excessive energy utilization and psychologic stress. 3. Further assessment of the neurophysiologic inhibition of GnRH production during childhood and the late prepubertal reactivation of the arcuate nucleus pulse generator. Roles of opioids, dopamine, other neurotransmitters, and metabolic signals remain to be clarified. 4. Exploration of regulators of hypothalamic, pituitary, and gonadal function when pulsatile GnRH administration has replaced the usual hypothalamic mechanisms. Pituitary-gonadal interactions may be independently assessed. 5. Assessment of pubertal growth, endocrine function, and neuropharmacologic control mechanisms in circumstances of chemical removal of pituitary gonadotrope function by GnRH agonists or antagonists. 6. Concordance and discordance of potency estimates of gonadotropins made by bioassay and immunoassay. The biologic basis for qualitative changes in bioassayable levels of LH and FSH, often related to carbohydrate content of the glycoprotein, may help to explain changes of gonadal function during the pubertal process. The potential for significant molecular heterogeneity of the gonadotropins is recognized and suggests substantial posttranslational changes of LH and FSH. 7. A cogent delineation of the hormonal, nutritional, and energy regulators of the pubertal growth spurt, though not discussed in this manuscript, remains to be accomplished. The relationship between pituitary gonadotropins and growth hormone, sex steroids, and the various peptide growth factors, especially the relationship between the growth factors and intragonadal steroidogenesis and germ-cell production, remain to be resolved. The importance of local production and action of peptide-growth factors in diverse tissues, skeletal and other, is being increasingly recognized.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Opioid control of LH secretion in humans: menstrual cycle, menopause and aging reduce effect of naloxone but not of morphine

A number of studies have been made on the role played by endogenous opioid peptides in the secretion of LH in humans. However no previous studies have compared the effects of the most potent pharmacological agonist and antagonist, morphine and naloxone, in the same subjects. The present study examined the acute effects of injections of morphine and naloxone on plasma LH levels in 30 healthy subjects (18 women and 12 men). Fertile women were subdivided into follicular (n = 6) and luteal (n = 6) phase groups; the remaining 6 were postmenopausal women. The 12 men were sub-divided in two groups of 6 subjects according to age (24-33 years, and over 60 years). There was a two day interval between injection studies in the same subjects. Morphine significantly decreased plasma LH levels in all groups examined (P less than 0.01). On the other hand, naloxone caused a significant increase in plasma LH levels in fertile women during the luteal phase of the cycle, but not during the follicular phase or in postmenopausal subjects, and in young but not in aged men (P less than 0.01). These results indicate that in humans there is a change in the activity of the opioids regulating LH secretion during the menstrual cycle, after menopause and in aged men and that these may be studied by the use of naloxone. The inability of naloxone under certain conditions to increase LH levels reflects the decreased activity of the endogenous system, while morphine, being active in all the subjects, seems to be less discriminative, at least in physiological conditions.

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.

Cluster analysis: a simple, versatile, and robust algorithm for endocrine pulse detection

Endocrine signaling provides one critical means of physiological communication within an organism. Many endocrine signals exhibit an episodic or pulsatile configuration. In an effort to provide a versatile and statistically based algorithm for investigating the regulation of endocrine pulse signals, we have formulated a computerized algorithm in which a pulse is defined as a statistically significant increase in a "cluster" of hormone values followed by a statistically significant decrease in a second cluster of values. The increase or decrease is judged in relation to the actual experimental error expressed by the replicates in the presumptive nadir and peak data clusters. The program permits the operator to specify the cluster sizes of test peaks and pre- and postpeak nadirs. This method is largely insensitive to unstable base-line hormone concentrations and is not adversely affected by varying pulse amplitudes, widths, or configurations within the endocrine series. In addition, the simple statistical basis for this algorithm renders it minimally dependent on explicit or a priori assumptions about rates of hormone secretion or disappearance. The program has been validated for false-positive errors against a wide range of intraseries coefficients of variation (4-52%). We have illustrated its performance for profiles of luteinizing hormone, follicle-stimulating hormone, growth hormone, prolactin, adrenocorticotropic hormone, and cortisol and compared these episodic patterns with those of stable serum constituents (total serum protein and calcium), which do not exhibit pulsatile fluctuation.

Detection and characterization of peaks and estimation of instantaneous secretory rate for episodic pulsatile hormone secretion

We have developed a new computer program for detection of "peaks" in sequential hormone measurements in longitudinal studies of episodic hormone secretion. The program provides: (a) several statistically based approaches to the estimation of the random measurement error as a function of hormone level; (b) peak detection based on analysis of first derivatives with logic that has been optimized for asymmetrical peaks with exponential decays; (c) several approaches to the estimation of tolerances for the first and second derivatives; (d) a sensitive curve-fitting approach, to distinguish between upstrokes, exponential decays, and flat baselines; (e) ability to detect multiple overlapping peaks; (f) analysis of "robustness" by systematically varying the threshold around the most-likely value; (g) superimposition of detected peaks, to evaluate "average peak shape"; (h) analysis of the "decay rate," to obtain an estimate of the disappearance rate constant and half-life; (i) use of a "discrete deconvolution" approach, to solve for the apparent instantaneous rate of secretion, and provision of an error analysis to obtain estimates of the precision of these derived values; and (j) correlation with other relevant series as a means of cross validating. The program has been tested extensively on real and synthetic data, and appears to perform well. The frequency of "false positive" peaks can be held at any desired low level, and can be prevented from increasing as sampling frequency increases. The number of arbitrary assumptions, approximations, or thresholds is held to an absolute minimum. These methods are natural, logical, and follow from first principles of statistics.

Naloxone increases bioactive LH in man: evidence for selective release of early LH pool

Opioid peptides inhibit LH secretion and the opiate antagonist naloxone provokes increases in plasma LH levels by release of endogenous GnRH from the hypothalamus. To explore the effect of endogenously released GnRH on the mobilization of bioactive LH pools, the bioactive LH response to a single iv bolus dose of 20 mg naloxone has been evaluated and compared to the immunoactive pattern of the hormone in eight young normal male volunteers. Blood samples were withdrawn at 15, 30, 45, 60, 90, 120 min after naloxone injection and LH levels were measured by RIA and rat interstitial cell testosterone (RICT) bioassay. A significant increase in both bio and immuno active LH was observed in all subjects after 15-30 min (p less than 0.05 to p less than 0.001), reaching maximal levels at 30-60 min for both forms of the hormone. The time course of the bioactive LH response magnified the immunoactive LH pattern, and the maximum fold increases were 1.4 and 1.3 fold (62.4 +/- 5.5 SE and 25.0 +/- 3.7 SE mIU/ml) from basal bio and immuno LH levels of 25.9 +/- 4.3 SE and 11.1 +/- 2.0 SE mIU/ml respectively. An early single peak response of bio and immunoactive LH was observed in six subjects while a biphasic pattern was observed in two subjects with a clearly defined and prominent early pool followed by a second pool of higher magnitude. Both bio and immunoactive LH levels began to decline at 45-60 min, but in most subjects remained significantly elevated by about 30% above the basal values at 120 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term effects of ovariectomy: the opioid control of LH secretion in fertile climacteric and postmenopausal women

The aim of this study was to evaluate the activity of opiate receptors involved in the regulation of LH secretion in relationship to ovariectomy. Menstruating fertile (n = 5) and climacteric (n = 7) patients and postmenopausal (n = 5) women who underwent therapeutical bilateral ovariectomy were studied in the first week postsurgery and LH plasma levels were evaluated after naloxone (4 mg in bolus plus 4 mg infusion/90 min), LHRH (10 micrograms + 10 micrograms iv) and saline administration. Two groups of fertile (n = 6) and postmenopausal (n = 6) subjects were studied as controls. Since the LH responsiveness to naloxone was impaired in climacteric patients after ovariectomy, the test was repeated in 5 of them after 1 and 6 months of estrogen-gestagen treatment (conjugated estradiol + noretisterone acetate), showing a significant increase in all patients in both cases. In four subjects treated with only gestagen, naloxone was still unable to significantly modify LH plasma levels. These results indicate that ovariectomy affects the activity of opiate receptors, resulting in the first week postsurgery LH rise inversely related to basal LH levels. Furthermore, these results indicate that one or six cycles of estrogen-gestagen treatment in ovariectomized patients similarly induces a restoration of the opiate receptors neuroendocrine activity.

Performance of LH pulse-detection algorithms at rapid rates of venous sampling in humans

To assess the influence of the sampling rate on the quantitative characterization of pulsatile luteinizing hormone (LH) release, we withdrew blood at 4-min intervals for 8 h in five men and at 1-min intervals for 2 h in six other men. For comparative purposes, significant LH pulses were enumerated by three independent, computerized pulse-detection algorithms currently available. Our results indicate that, although the absolute number of LH pulses detected was influenced by the particular algorithm used and the estimate of intra-assay variance, all three analyses yielded increased pulse-frequency estimates at more intensive rates of venous sampling. Moreover, using a fourth, modified pulse-detection algorithm intended to maximize recognition of true-positive LH pulses while minimizing both false-positive and false-negative pulses, we observed that venous sampling at 4- and 1-min intervals exposed 4- and 12-fold more LH pulses, respectively, than could be discerned at conventional sampling rates. At rapid rates of venous sampling, the pattern of LH pulses comprised high-frequency, low-amplitude LH pulsations superimposed on lower-frequency LH peaks. This pattern suggests that the pituitary gland is responsive to high rates of intermittent neural stimulation. Moreover, these observed profiles are consistent with rapid initial rates of LH disappearance and/or distribution that we could demonstrate after intravenous bolus injections of purified LH in hypogonadotropic volunteers. In conclusion, we have compared results from three different pulse-detection algorithms at various rates of venous sampling and demonstrated a critical influence of sampling rate on apparent LH pulse frequency in humans.

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)

Pulsatile secretion of gonadotropins and prolactin in male marathon runners. Relation to the endogenous opiate system

We tested the hypothesis that sustained, strenuous physical training alters the neuroendocrine regulation of pulsatile gonadotropin and/or prolactin secretion in men. Blood was sampled at 20-minute intervals over 8 hours in five endurance-trained men after a 10-15 mile run in the middle of the active training season, and in 11 nonendurance trained normal controls. In these two groups, basal patterns of physiologically pulsatile secretion of LH, FSH, and prolactin (PRL) were not significantly different in relation to the following parameters: mean serum concentration of each of the three hormones (N = 25 samples); areas under the hormone concentration vs. time curves; fractional, incremental, and absolute pulse amplitudes; and pulse frequency, or periodicity. To test for enhanced suppressive effects of endogenous opiates in trained male marathon runners, subjects were administered the potent opiate-receptor antagonist, naltrexone (1 mg/kg). This antagonist significantly stimulated pulsatile LH secretion by increasing mean serum LH values from 10.94 to 13.58 mIU/ml (P = 0.007); area under the LH concentration vs. time curve increased from 5370 to 6510 mIU/ml X 8 hours (P = 0.05) and, pulse frequency rose from 2.8 to 4.9 pulses/8 hours (P = 0.006). Naltrexone also enhanced pulse frequency of FSH secretion from 3.4 to 5.4 pulses/8 hours (P = 0.009), but did not alter serum prolactin concentrations. None of these responses differed significantly from those in normal sedentary controls.(ABSTRACT TRUNCATED AT 250 WORDS)