Opioid control of luteinizing hormone secretion in humans

Assessing men with opioid use disorder for testosterone deficiency after the development of symptoms

OBJECTIVE

Individuals with opioid use disorder (OUD) have reduced life expectancy and inferior outcomes when treated for depression, diabetes, and fractures. Their elevated risk of testosterone deficiency may contribute to all of these relationships, however few individuals prescribed opioids are evaluated with testosterone assays. The purpose of this study is to determine whether patients with opioid use disorder are evaluated for testosterone deficiency after development of a symptom that may merit investigation, such as erectile dysfunction (ED).

METHOD

We conducted a retrospective longitudinal cohort study that utilized data from a national database called TriNetX. Patients were eligible for inclusion if they were 20 to 90 years of age, male, and diagnosed with erectile dysfunction. We utilized descriptive statistics and logistic regression to address study aims.

RESULTS

Testosterone testing was uncommon for all patients with ED. Among 20,658 patients, it was assessed in 11.2% with OUD and 15.1% without OUD. Among those screened, 40% individuals with OUD and ED had testosterone deficiency. Odds of screening those with OUD were lower than matched controls (RR 0.74).

CONCLUSIONS

Individuals with OUD are at increased risk of testosterone deficiency than the general population, but nearly 90% are not evaluated for this condition even after development symptoms. That 40% of individuals assessed were classified as testosterone deficient suggests endocrine disorders may be contributing to increased fracture risk, chronic pain, and severe depression commonly encountered in patients with OUD. Addressing this care gap may reduce morbidity and mortality associated with opioid use disorder.

Administration of Very Low Doses of Estradiol Modulates the LH Response to a GnRH Bolus and the LH and Cortisol Responses to Naloxone Infusion in Patients with Functional Hypothalamic Amenorrhea (FHA): A Pilot Study

Background: Functional Hypothalamic Amenorrhea (FHA) is a stress-induced blockade of the reproductive axis. Such impairment is mainly due to altered control of GnRH-induced gonadotropin secretion as well as alterations of other endocrine functions. Methods: Seventeen patients with FHA participated in the study. Basal hormonal profiles and GnRH and Naloxone tests for LH (Luteinizing Hormone) and for LH and cortisol responses, respectively, were performed before and after two weeks of administration of a very low dose of estradiol (2.5 ng two times a day). Results: The treatment improved both gonadotropins, mainly LH. The LH response to the GnRH test improved in terms of the peak amplitude, as evaluated using Instantaneous Secretory Rates (ISR) computation. Moreover, when performing the Naloxone test after the treatment interval, FHA patients showed a quicker LH response and recovery of the cortisol response. Conclusions: Our study supports the relevance of very low dose estradiol priming to promote and restore impaired neuroendocrine function in patients with FHA.

Orphanin FQ-ORL-1 regulation of reproduction and reproductive behavior in the female

Orphanin FQ (OFQ/N) and its receptor, opioid receptor-like receptor-1 (ORL-1), are expressed throughout steroid-responsive limbic and hypothalamic circuits that regulate female ovarian hormone feedback and reproductive behavior circuits. The arcuate nucleus of the hypothalamus (ARH) is a brain region that expresses OFQ/N and ORL-1 important for both sexual behavior and modulating estradiol feedback loops. Within the ARH, the activation of the OFQ/N-ORL-1 system facilitates sexual receptivity (lordosis) through the inhibition of β-endorphin neuronal activity. Estradiol initially activates ARH β-endorphin neurons to inhibit lordosis. Simultaneously, estradiol upregulates coexpression of OFQ/N and progesterone receptors and ORL-1 in ARH β-endorphin neurons. Ovarian hormones regulate pre- and postsynaptic coupling of ORL-1 to its G protein-coupled signaling pathways. When the steroid-primed rat is nonreceptive, estradiol acts pre- and postsynaptically to decrease the ability of the OFQ/N-ORL-1 system to inhibit ARH β-endorphin neurotransmission. Conversely, when sexually receptive, ORL-1 signaling is restored to inhibit β-endorphin neurotransmission. Although steroid signaling that facilitates lordosis converges to deactivate ARH β-endorphin neurons, estradiol-only facilitation of lordosis requires the activation of ORL-1, but estradiol+progesterone does not, indicating that multiple circuits mediate ovarian hormone signaling to deactivate ARH β-endorphin neurons. Research on the role of OFQ/N-ORL-1 in ovarian hormone feedback loops is just beginning. In the rat, OFQ/N may act to terminate gonadotropin-releasing hormone and luteinizing hormone release under positive and negative feedbacks. In the ewe, it appears to directly inhibit gonadotropin-releasing hormone release to mediate progesterone-negative feedback. As a whole, the localization and actions of OFQ/N-ORL-1 system indicate that it may mediate the actions of estradiol and progesterone to synchronize reproductive behavior and ovarian hormone feedback loops.

Physiology, pathology and pharmacology of the male reproductive system

The male reproductive system consists of the testes, a ductal system and sex accessory organs. Production of sperm by the testes combined with fluids formed by the sex accessory organs (e.g. seminal vesicles, prostate and bulbourethral glands) produce a secretion that supports the survival of spermatozoa and provides a medium through which they can move through the reproductive ducts (e.g. epididymis, vas deferens, ejaculatory duct and urethra) for ejaculation of viable sperm into the female reproductive tract. Summarized herein are the essentials of normal male reproductive physiology, disorders of male sexual differentiation, pharmacological therapy of common diseases of the male genitourinary tract and the impact of drugs of abuse on the male reproductive system.

Absence of an opioid stimulatory tone on growth hormone secretion in women with microprolactinoma

INTRODUCTION

Literature data suggest that prolactinoma is a tumor with a complex pathogenesis and that its growth is the result of changes at the pituitary and/or hypothalamic level. Abnormal release of hypothalamic factors (including endogenous opioid peptides) may contribute to prolactinoma development. An increased endogenous opioid tone (EOT) occurs in patients with prolactinoma, and seems to play an important role in pituitary secretion, as suggested by the ability of the opiate receptor antagonist naloxone to stimulate luteinizing hormone pulsatile secretion in these patients.

OBJECTIVE

To investigate the effect of the EOT on growth hormone (GH) secretion in women with prolactinoma.

DESIGN

Eleven women aged 30.4+/-6.7 years (range 20-41), with an established diagnosis of microprolactinoma, were studied. GH-releasing hormone (GHRH), 100 microg as an intravenous (i.v.) bolus, was administered with and without preadministration of i.v. naloxone, an opioid receptor antagonist, 2 mg as a bolus followed by a constant infusion of 1.6 mg/h. Blood samples were taken for 120 min after GHRH administration.

RESULTS

Naloxone did not affect the GH response to GHRH, measured as single times, mean peak values, or as integrated concentrations.

CONCLUSION

Our data suggest that an opioid stimulatory tone on GH secretion in women with prolactinoma is absent.

Black cohosh (Actaea racemosa, Cimicifuga racemosa) behaves as a mixed competitive ligand and partial agonist at the human mu opiate receptor

Black cohosh is a commonly used botanical dietary supplement for the treatment of climacteric complaints. Because the opiate system in the brain is intimately associated with mood, temperature, and sex hormonal levels, the activity of black cohosh extracts at the human mu opiate receptor (hMOR) expressed in Chinese hamster ovary cells was investigated. The 100% methanol, 75% ethanol, and 40% 2-propanol extracts of black cohosh effectively displaced the specific binding of [3H]DAMGO to hMOR. Further studies of the clinically used ethanol extract indicated that black cohosh acted as a mixed competitive ligand, displacing 77 +/- 4% [3H]DAMGO to hMOR (Ki = 62.9 microg/mL). Using the [35S]GTPgammaS assay, the action of black cohosh was found to be consistent with an agonist, with an EC50 of 68.8 +/- 7.7 microg/mL. These results demonstrate for the first time that black cohosh contains active principle(s) that activate hMOR, supporting its beneficial role in alleviating menopausal symptoms.

G-protein coupled receptor oligomerization in neuroendocrine pathways

Protein-protein interactions are fundamental processes for many biological systems including those involving the superfamily of G-protein coupled receptors (GPCRs). A growing body of biochemical and functional evidence supports the existence of GPCR-GPCR homo- and hetero-oligomers. In particular, hetero-oligomers can display pharmacological and functional properties distinct from those of the homodimer or oligomer thus adding another level of complexity to how GPCRs are activated, signal and traffick in the cell. Dimerization may also play a role in influencing the activity of agonists and antagonists. We are only beginning to unravel how and why such complexes are formed, the functional implications of which will have an enormous impact on GPCR biology. Future research that studies GPCRs as dimeric or oligomeric complexes will enhance not only our understanding of GPCRs in cellular function but will also be critical for novel drug design and improved treatment of the vast array of GPCR-related conditions.

Distribution of beta-endorphin and substance P in the shoulder joint of the dog before and after a low impact exercise programme

Beta-endorphin and substance P were immunolocalized in the articular cartilage, synovial membrane and fibrous joint capsule of dogs. Twelve adult greyhounds were randomly assigned to one of three groups: control, limited exercise, or regimented exercise. On day 0, biopsies of articular cartilage and joint capsule were obtained from the left shoulder joints of dogs receiving limited and regimented exercise. On day 72, biopsies of joint capsule from right and left shoulders and articular cartilage from the right shoulder joint were analysed for the presence of glycosaminoglycans (GAG) and for immunolocalization of substance P and beta-endorphin. Regimented exercise increased the presence of GAGs and immunolocalization of substance P and beta-endorphin in articular cartilage and synovial membrane compared to day 0 biopsies and untreated controls. Localization of beta-endorphin became prominent in and around the chondrocytes. Substance P was increased in chondrocytes and extracellular matrix. Concomitant changes in localization of beta-endorphin and substance P may have a role in the modulation of the microphysiological environment, metabolism, or function of joint tissues in response to low-impact exercise.

Circulating levels of immunoreactive beta-endorphin in polycystic ovary syndrome

The plasma levels of beta-endorphin were studied in 64 women with polycystic ovarian disease (PCOD), from whom was selected a group of 23 women with normal weight and amenorrhea of < 36 days. On day 21, beta-endorphin levels were: mean 64.92 pg/ml; SD 37.32 pg/ml; 95% CI 48.38-81.47 pg/ml. It was also observed that their levels of opioid peptide were reduced, compared with women who had normal ovulatory cycles, both in the follicular phase (mean 70.93 pg/ml; SD 24.59 pg/ml; 95% CI 76.84-99.77 pg/ml) and luteal phase (mean 88.30 pg/ml; SD 31.80 pg/ml; 95% CI 76.84-99.77 pg/ml). The results were statistically significant (p < 0.05) for levels in PCOD patients compared with those of the luteal phase in women with normal ovulatory cycles. The decreased levels of beta-endorphin were negatively related to luteinizing hormone (LH) levels, which might explain the rise of LH levels in women with PCOD who control their weight and at the time of amenorrhea, although it is not clear if central opioid activity is reflected in the peripheral blood.

Blockade of the oestrogen-induced luteinizing hormone surge in ovariectomized ewes by a highly selective opioid mu-receptor agonist: evidence for site of action

Endogenous opioid systems in the hypothalamus inhibit gonadotropin-releasing hormone (GnRH) secretion, and a reduction in this inhibitory input (disinhibition) is thought to be part of the neural mechanism of the preovulatory GnRH/luteinizing hormone (LH) surge. We showed previously that intracerebroventricular infusion of the highly specific opioid mu-receptor agonist DAMGO delayed the oestrogen-induced LH surge in ovariectomized (OVX) ewes, whereas both delta- and kappa-agonists were ineffective. The aim of the present study was to establish the anatomical site of this effect. The most likely hypothalamic sites of action are the medial preoptic area (MPOA), where most GnRH perikarya are located in sheep, and/or the median eminence (ME), where GnRH fibres terminate on hypophysial portal blood vessels. Conscious, unrestrained OVX ewes with permanent bilateral guide tubes implanted into either the MPOA or the mediobasal hypothalamus (MBH), close to the ME, were injected (i.m.) with oestradiol benzoate (EB) 50 microg (t = 0 h). In this model, EB elicits a time-delayed surge in LH secretion after 13-19 h. Jugular venous blood was sampled at half-hourly intervals from -2 to 0 h, and from 10 to 26 h. From 12 to 20 h, bilateral infusions of either the highly specific opioid mu-agonist DAMGO (40 nmol/h bilaterally) or saline were given into the MPOA or MBH at 2.5 microl/h. Guide tube placements were confirmed histologically. The mean (+/- SEM) time to the onset of the LH surge was significantly (p < 0.01) increased in the animals (n = 9) that received DAMGO infusion into the MPOA (20.5 +/- 1.4 vs. 15.7 +/- 0.6 h in the saline-infused controls). The effect was clearly apparent in 6/9 of the DAMGO-infused animals. The mean (+/- SEM) time to LH surge onset was also significantly (p < 0.01) increased in the animals (n = 8) that received DAMGO infusion into the MBH (19.7 +/- 1.2 vs. 14.3 +/- 0.5 h). In this case, the effect was clearly apparent in 4/8 of the DAMGO-infused animals. We conclude that bilateral infusion of DAMGO into either the MPOA or the MBH can delay the EB-induced LH surge in OVX ewes. These data provide further evidence for dual hypothalamic sites of opioid regulation of GnRH secretion, and are consistent with the hypothesis that disinhibition from opioid tone at both the MPOA and MBH/ME is permissive of the preovulatory GnRH/LH surge.

Opioid peptides inhibit the estradiol-induced proliferation of cultured rat uterine cells

The effect of opioid peptides on estradiol-induced cell proliferation in adult rat uterine primary cell cultures was studied. Estradiol increased cell density by 40%. This estradiol-induced stimulation of cell proliferation was decreased to control values by [D-Met2,Pro5]enkephalinamide. The opioid-induced inhibition of uterine cell proliferation was blocked completely by the specific opiate antagonist naloxone, while naloxone did not have any effect on its own. The inhibition of cell proliferation by enkephalinamide was apparent at each stimulatory estradiol concentration examined. This opioid effect was mediated mainly by the mu opiate receptor. The observed effects occurred within the physiological nanomolar concentration range. Enkephalinamide did not have any effect on the basal proliferation rate of adult rat uterine cells. However, enkephalinamide inhibited the basal rate of cell proliferation in cell cultures prepared from 7-day-old immature rats. In summary, here we present evidence of novel physiological direct cross-talk between the opioid and estrogenic signaling systems in the regulation of normal uterine growth.

Plasma levels of beta-endorphin during the menstrual cycle

During recent years, many research teams have suggested a possible role of endogenous opiates in the control of the menstrual cycle. The level of immunoreactive beta-endorphin was measured on different days during the ovulatory cycle of 131 healthy volunteers. The levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17 beta-estradiol and progesterone were also measured. The graphic representation of opiate levels during the female menstrual cycle, where day O is the day of ovulation, shows that plasmatic beta-endorphin levels are not stable throughout. The levels increase progressively during the follicular phase, reaching a maximum (mean 139.49 pg/ml, SD 42.23 pg/ml, 95% confidence interval 121.22-157.75 pg/ml) 4 days before ovulation. During the periovulatory period (days-3 to +3) levels of beta-endorphin are very stable (mean day 0, 27.8 pg/ml, SD 6.36 pg/ml, 95% confidence interval 19.29-27.83 pg/ml) and low (p < 0.05), followed by a renewed increase during the luteal phase (mean day + 5, 87.86 pg/ml, SD 36.49 pg/ml) where a maximum level (mean 102.78 pg/ml, SD 30.35 pg/ml) is reached 24 h before the next menses. The beta-endorphin level has a negative correlation with the LH level (r = -0.50, p < 0.001) on the preovulatory days, and during the luteal phase a positive linear correlation (r = 0.47, p < 0.001) is found with the progesterone level. It seems that beta-endorphin levels in the plasma are influenced by the ovarian steroids. However, the influence of the plasmatic opiate on the gonadotropins is currently under discussion.

Functional analysis of cloned opioid receptors in transfected cell lines

Opioids modulate numerous central and peripheral processes including pain perception neuroendocrine secretion and the immune response. The opioid signal is transduced from receptors through G proteins to various different effectors. Heterogeneity exists at all levels of the transduction process. There are numerous endogenous ligands with differing selectivities for at least three distinct opioid receptors (mu, delta, kappa). G proteins activated by opioid receptors are generally of the pertussis toxin-sensitive Gi/Go class, but there are also opioid actions that are thought to involve Gq and cholera toxin-sensitive G proteins. To further complicate the issue, the actions of opioid receptors may be mediated by G-protein alpha subunits and/or beta gamma subunits. Subsequent to G protein activation several effectors are known to orchestrate the opioid signal. For example activation of opioid receptors increases phosphatidyl inositol turnover, activates K+ channels and reduces adenylyl cyclase and Ca2+ channel activities. Each of these effectors shows considerable heterogeneity. In this review we examine the opioid signal transduction mechanism. Several important questions arise: Why do opioid ligands with similar binding affinities have different potencies in functional assays? To which Ca2+ channel subtypes do opioid receptors couple? Do opioid receptors couple to Ca2+ channels through direct G protein interactions? Does the opioid-induced inhibition of vesicular release occur through modulation of multiple effectors? We are attempting to answer these questions by expressing cloned opioid receptors in GH3 cells. Using this well characterized system we can study the entire opioid signal transduction process from ligand-receptor interaction to G protein-effector coupling and subsequent inhibition of vesicular release.

Growth hormone deficiency coupled with hypogonadism in AIDS

Both growth hormone and sex steroid deficiencies are known to affect quality of life adversely. Hypogonadism is not infrequent in patients with AIDS and due mostly to hypothalamic or end-organ failure. The prevalence of GH deficiency is unknown. We report two cases of GH deficiency in AIDS, one of which was associated with gonadotroph failure. The significance of GH deficiency in HIV infection in terms of its potential effects on disease progression is discussed. Further studies are required to assess the prevalence of GH deficiency and to clarify its role in the immunopathogenesis of AIDS.

Ovarial steroids and methionine-enkephalin modulation of adrenergic transmission in rabbit oviduct

1. The effect of methionine-enkephalin on the [3H]-noradrenaline ([3H]-NA) overflow and on contractions evoked by field electrical stimulation (FES) and by exogenous NA were studied in vitro in the isthmic part of oviduct of rabbits (untreated and treated with estradiol or progesterone). 2. The evoked tritium overflow (which reflected [3H]-NA overflow) was determined by liquid scintillation spectrometry. 3. Field electrical stimulation of 4 Hz (trains of 40 pulses, 0.3 msec) evoked guanethidine-sensitive contractions. 4. In all groups of animals methionine-enkephalin dose dependently decreased FES-evoked contractions but not those evoked by exogenous NA. 5. The amount of tritium overflow evoked by 4 Hz stimulation (600 pulses, 1 msec) was significantly lower in tissues from estradiol treated (1.16 +/- 0.19%) compared with those obtained in tissues from untreated (1.82 +/- 0.22%) and progesterone treated (2.07 +/- 0.21%) rabbits. Methionine-enkephalin, 1 microM, decreased the evoked tritium overflow in the isthmus from untreated rabbits by 36.1 +/- 3.6%, in estradiol treated by 22.8 +/- 2.9% and in progesterone treated by 52.3 +/- 4.5%. 6. The results suggest that the methionine-enkephalin effect on FES-evoked contractions could be due to a prejunctional effect on the adrenergic terminals and that there is a hormonal dependence of the opioid effect on [3H]-NA overflow.

The effects of opioid blockade and GnRH administration upon luteinizing hormone secretion in patients with anorexia nervosa during the stages of weight loss and weight recovery

OBJECTIVE

We examined the functional status of the hypothalamic-opioid system involved in LH secretion and the pituitary LH sensitivity and reserve in patients with anorexia nervosa were studied during body weight loss and weight recovery. We measured the temporal relationship between weight recovery, expression of hypothalamic-opioid activity and pituitary GnRH responsiveness, and resumption of ovulatory cycles.

DESIGN

Five patients with anorexia nervosa were prospectively studied during weight loss and amenorrhoea, subsequently when they reached their ideal body weight but still remained amenorrhoeic and thereafter every 6 months until resumption of ovulatory cycles; one patient was studied only during weight loss, two during ideal body weight and amenorrhoea and one during ideal body weight and ovulatory cycles. Blood was sampled every 10 minutes over a 16-hour period on two alternate days. On study day 1 (control day), patients received two sets of saline infusion every 6 hours and one saline bolus at the beginning of the seventh hour; on study day 3 (experimental day), they received a saline infusion during the first 6 hours, an intravenous bolus of naloxone (20 mg) at the beginning of the seventh hour and then a continuous naloxone infusion (1.6 mg per hour) during the ensuing 6 hours. Pituitary LH sensitivity and reserve were assessed on both study days by the subsequent administration of 5 and 95 micrograms of GnRH 4 hours before the completion of each sampling period. Patients in ideal body weight and ovulatory cycles as well as five normal menstruating women included in the study for comparative purposes, were studied during the midluteal phase of a cycle.

MEASUREMENTS

LH, oestradiol and progesterone were determined by radioimmunoassay. Areas under the LH curve were calculated by the trapezoid method; LH pulse detection was carried out by the program Cluster.

RESULTS

Naloxone administration to patients with anorexia nervosa in the weight loss phase, did not significantly modify their serum LH levels nor the characteristics of its pulsatile secretion. Administration of the opioid blocker induced a significant increase in serum LH concentrations only in those patients in ideal body weight and amenorrhoea who resumed ovulatory cycles within the 6 months following the last study as well as in patients with an ideal body weight and ovulatory cycles and in normal controls. All patients and subjects who responded to naloxone administration exhibited significant increases in the area under the LH curve, mean LH pulse amplitude and peak area. Patients in ideal body weight and amenorrhoea who did not resume ovulatory cycles within the 6 months following the study days, did not respond to naloxone administration. There were no significant correlations between the magnitude of LH response to naloxone administration and the baseline levels of serum oestradiol and progesterone. All patients exhibited significant pituitary LH responses to both GnRH doses, regardless of the stage of the disease; however, the pituitary responsiveness shown by patients in ideal body weight was significantly higher than that presented by patients in weight loss. There were no significant differences between the responses to GnRH exhibited by patients in ideal body weight and amenorrhoea who responded to naloxone administration and those shown by patients in the same clinical condition but who were insensitive to opioid blockade.

CONCLUSIONS

The re-establishment of hypothalamic-opioid inhibitory activity involved in LH secretion in patients with anorexia nervosa during the phase of weight gain predicts imminent restoration of ovulatory cycles. Pituitary LH response to exogenous GnRH during weight recovery does not accurately predict the outcome of the disease regarding reinitiation of menstrual cycles; however, it might be an indicator that the normal function of the hypothalamic-pituitary axis is being restored.

Effect of naloxone and beta-casomorphin on the hypothalamic-pituitary-luteinizing hormone axis in vitro

The effect of naloxone and beta-casomorphin on luteinizing hormone (LH) release from pituitary cell aggregates, obtained by three-dimensional culture, with or without mediobasal hypothalamic fragments was studied in vitro. Short-term naloxone perifusion at a concentration of 10(-5)M did not modify either basal or LHRH-stimulated LH release from the pituitary cell aggregates. In contrast, a 12-min naloxone perifusion at the same concentration caused an increase in LH release in the mediobasal hypothalamic-pituitary cell aggregate axis. This increase was rapid (12-16 min after time pulse), marked [up to 10 times (p less than 0.004) the initial base line], short (return to the base line secretion 32-40 min after the beginning of the time pulse) and dose-dependent, with a rise greater than 1000% at a concentration of 10(-4) (p less than 0.006). The same effect was observed when a second pulse was applied 48 min after the first one. LH release induced by naloxone was antagonized 56 +/- 2% (p less than 0.03) by beta-casomorphin (an exogenous opiate) at a concentration of 10(-5) M. beta-casomorphin alone did not modify LH basal secretion, but inhibited 25.1 +/- 2.4% (p less than 0.008) LH release enhanced by LHRH. These results indicate that naloxone, an opiate antagonist, markedly increases LH release via a mu-type opioid receptor mechanism at the hypothalamic level only, during short-term exposure.