Effect of androgens on penile tissue

There are two ways to establish that androgens play a major role in the function and integrity of erectile tissue: (1) discussing a number of physiology and molecular biology studies that have been published from experiments in animals and (2) reporting the effect of androgens on penile tissue, or in many cases the lack of androgen, in man. A variety of animal models, and also human studies, have shown the existence of androgen receptors in the corpora cavernosa. The penile erectile response in the laboratory rat is androgen dependent, and the active androgen appears to be dihydrotestosterone. There are several articles that describe the androgenic regulation of nitric oxide synthase (the enzyme responsible for production of nitric oxide), the primary agent controlling the erectile cycle. There have been few reports showing a direct end organ dependency of androgen for erectile function in the human corpora cavernosa, although there is plenty of evidence demonstrating that low or absent androgens affect a man’s ability to have an erection in a sexual situation. Thus, in man androgen dependency for cavernous tissue smooth muscle function is still debatable. Extrapolating animal dependency of androgens for molecular activity in the penile tissue remains the most reasonable suggestion for androgen dependency of the cavernous tissue in man.     

Lean rats with hypothalamic pro-opiomelanocortin overexpression exhibit greater diet-induced obesity and impaired central melanocortin responsiveness

Aims/hypothesis Central pro-opiomelanocortin (Pomc) gene therapy ameliorates genetic- or age-related obesity. We hypothesised that this treatment would delay or prevent dietary obesity in young, lean rats. Materials and methods Recombinant adeno-associated virus encoding Pomc (rAAV-Pomc) was delivered bilaterally into the basomedial hypothalamus of lean rats for 42 days. Food intake, body weight, serum hormones, brown adipose tissue (BAT) uncoupling protein 1 (UCP1) and mRNA levels of hypothalamic neuropeptides and melanocortin receptors were assessed. Beginning on day 43, half of the rats remained on chow while the others received a high-fat diet for 89 days. We examined energy balance and responsiveness to the melanocortin agonist melanotan II (MTII) or the antagonist SHU9119. Results Pomc gene delivery produced elevated hypothalamic Pomc mRNA (fourfold) and α-melanocyte-stimulating hormone levels in the arcuate nucleus (twofold). Food intake and body weight were not altered by rAAV-Pomc in rats fed standard-chow. In rAAV-Pomc rats at day 42, perirenal fat and serum leptin decreased but overall visceral adiposity did not; expression of the hypothalamic agouti-related protein (Agrp) mRNA was elevated, whereas expression of melanocortin 3 and 4 receptor mRNA was reduced; BAT UCP1 protein increased nearly fourfold. The rAAV-Pomc rats fed the high-fat diet consumed more energy and gained more body weight compared with chow- or high-fat-fed controls that did not receive Pomc gene delivery. The anorexic response to MTII was impaired, whereas the orexigenic effect of SHU9119 was enhanced by rAAV-Pomc pretreatment. Conclusions/interpretation Delivery of the Pomc gene alters energy homeostasis in lean rats, predisposing them to diet-induced obesity. Diminished hypothalamic melanocortin receptors, increased Agrp expression, and potential rewiring of brain circuits may underlie the exacerbated obesity.     

Suppression of hypothalamic pro-opiomelanocortin (POMC) gene expression by daily melatonin supplementation in aging rats

Both plasma melatonin levels and hypothalamic arcuate nucleus pro-opiomelanocortin (POMC) (biosynthetic precursor to the endogenous opioid ss-endorphin and other opiomelanocortins) mRNA content decrease with aging. To test whether the decline in melatonin is responsible for the decline in POMC mRNA, we investigated the effects of daily melatonin treatment on hypothalamic POMC mRNA content in middle-aged and older Sprague-Dawley rats. Daily nocturnal melatonin treatment (50 microg kg bw(-1) night(-1), in the night-time drinking water) for 7 months, starting at 13 months of age, did not significantly alter female arcuate nucleus POMC mRNA content determined at the end of the light period (i.e., before nightly melatonin administration), but suppressed (24%, P < 0.05) POMC mRNA content at the end of the dark period (i.e., following melatonin administration). Likewise, nocturnal administration of 50 or 500 microg melatonin kg bw(-1) night(-1) to male rats for 7 months suppressed (31 or 28%, respectively; P < 0.05) POMC mRNA content at the middle of the dark period at 20 months of age. Finally, 10 wk administration of 30 microg melatonin kg bw(-1) day(-1) suppressed (31%, P < 0.01) POMC mRNA content in middle-aged male rats killed at the end of the dark period. Melatonin treatments did not significantly alter estradiol or testosterone levels. Thus, moderate-dosage nocturnal melatonin supplementation suppressed nocturnal hypothalamic POMC gene expression in both middle-aged males and females, suggesting that melatonin supplementation during aging decreases, rather than increases, forebrain opiomelanocortinergic activity. These POMC responses were apparently not dependent on gonadal steroid responses and did not become refractory to melatonin treatment maintained until old age.     

Effect of histamine on the secretion of pro-opiomelanocortin derived peptides in rats

In conscious male rats intracerebroventricular infusion of histamine increased the plasma concentrations of ACTH and beta-endorphin immunoreactivity 2.5-fold (P less than 0.01). Gel filtration of plasma revealed two peaks of beta-endorphin immunoreactivity corresponding to beta-endorphin and beta-lipotropin. The two fractions increased almost equally in histamine-stimulated animals, whereas most of the circulating beta-endorphin immunoreactivity in control animals corresponded to beta-endorphin. Central infusion of the H1-receptor agonist 2-thiazolylethylamine and of the H2-receptor agonists dimaprit or 4-methylhistamine increased the plasma ACTH and beta-endorphin immunoreactivity concentrations 2- and 3-fold, respectively (P less than 0.01). Infused intracerebroventricularly, the H2-receptor antagonists cimetidine or ranitidine prevented the histamine-induced increase in plasma ACTH and beta-endorphin immunoreactivity (P less than 0.01), whereas the H1-receptor antagonist mepyramine inhibited the peptide responses by 70% (P less than 0.01). Infused intra-arterially cimetidine or ranitidine inhibited the histamine-induced increase in plasma ACTH by 80% (P less than 0.01) and plasma beta-endorphin immunoreactivity by 45% (P less than 0.05), whereas mepyramine or the other H1-receptor antagonist SKF-93944 inhibited the ACTH response by 50% (P less than 0.05), but had no effect on the beta-endorphin immunoreactivity. The results indicate that histamine increases the release of the pro-opiomelanocortin derived peptides ACTH, beta-lipotropin and beta-endorphin from the anterior pituitary lobe, whereas an effect of histamine on the release of beta-endorphin from the neurointermediate lobe is possible. The effect of histamine seems primarily mediated by H2-receptors, whereas H1-receptors appear to play a minor role.     

The regulation system of brain aromatase activity; effects of androgens on hypothalamic aromatase in the male rat

Recently, some studies have found the greatest aromatase activity in brain areas associated with sexual differention and sexual behavior, namely the hypothalamic and limbic structures. We studied the regulation of aromatase activity in the hypothalamic area of male rats, using a sensitive in vitro assay which measures the amount of 3H2O formed by tissue homogenates during the conversion of [1 beta-3H] androstenedione to estrogen. After castration, hypothalamic aromatase activity was significantly decreased (P less than 0.01), and seminal vesicle (SV) and prostate (PR) weights were also significantly decreased (P less than 0.01). Castrated male rats were given testosterone (T), 5 alpha-dihydrotestosterone (DHT), 5 alpha-androstane-3 alpha, 17 beta-diol (A3 alpha), 5 alpha-androstane-3 beta and 17 beta-diol(A3 beta) in various doses (200-1000 micrograms/day) for 10 days, and were given 600 micrograms/day T, DHT, A3 alpha and A3 beta for various durations (1-10 days). We found that T, DHT and A3 alpha but not A3 beta reversed the effects of castration on the hypothalamic aromatase activity. The order of this reversible effect of androgens was as follows: T greater than or equal to DHT greater than A3 alpha. T, DHT, A3 alpha and A3 beta increased SV and PR weights, and the order of this effect was as follows: DHT greater than T greater than A3 alpha much greater than A3 beta. We administered the antiandrogen (flutamide) to intact male rats (8 mg/day for 6 days). Flutamide decreased hypothalamic aromatase activity at the same level as that of castrated rats. Likewise, administration of both flutamide and T to castrated rats blocked the T-induced increase in hypothalamic aromatase activity and accessory sexual organ weight. From these results, we suggest that T, DHT and A3 alpha regulated hypothalamic aromatase activity, that T was the most effective of the androgens, and that was different from peripheral androgen target organs.     

Aromatase expression and activity in male and female cultured rat hypothalamic neurons: effect of androgens

Aromatase is possibly involved in male brain sexual differentiation. Aim of these experiments was to evaluate the role of testosterone (T) and of DHT, in the regulation of aromatase expression and activity. The experiments were done utilizing rat primary cultures of hypothalamic neurons from 16-day old embryos sex-screened by SRY gene. Aromatase expression was assessed semiquantitatively by RT-PCR using a neuronal marker (MAP2c) as coamplification product; enzymatic activity was estimated by the 3H(2)O method. The results indicate that (1) cultured neurons possess a functional aromatase, which increases significantly during a 5-days culture period; (2) neurons from males possess a higher expression and activity of the enzyme than females; (3) androgens negatively control expression/activity of aromatase in males, DHT is more active than T; (4) on the contrary, in females T produces a small stimulation of aromatase expression, but not of activity (DHT has produced inconsistent results). The results obtained in this model indicate that T does not stimulate aromatase; therefore, it is not responsible for triggering the perinatal enzymatic peak, nor for the sexual dimorphic aromatase expression. A model is proposed in which DHT might induce, at least in males, the descending phase of the aromatase peak.     

Ectopic pro-opiomelanocortin syndrome.

Ectopic POMC syndrome remains one of the most challenging differential diagnoses in endocrinology. Recent progress in the understanding of the tissue specific regulation of POMC gene expression and new insights into the processing of the POMC peptide in nonpituitary tissues has helped elucidate some of the molecular events leading to ectopic expression and secretion of POMC peptides. Corticotropin and other POMC-derived peptides have diverse effects on adrenal steroidogenesis, growth, and extra-adrenal tissues. Differences in POMC gene regulation in the corticotrope versus ectopic POMC-producing tumors provides a scientific framework for the clinical distinction between eutopic and ectopic Cushing's syndrome. In an attempt to revisit recent basic and clinical advances in the diagnosis of ectopic POMC syndrome the authors undertook an extensive literature review of 530 cases in 197 published papers and provided a molecular biologic, demographic and diagnostic update. According to this review, the four most common causes of ectopic POMC syndrome are the small cell carcinoma of the lung (27%), bronchial carcinoids (21%), islet cell tumor of the pancreas (16%), and thymic carcinoids (10%). Although the clinical features of patients with ectopic POMC syndrome are similar to those with Cushing's disease, subgroup analysis reveals a broad spectrum of severity and progression of signs and symptoms of hypercortisolism. The endocrine workup of a patient with suspected ectopic POMC syndrome includes the establishment of pathologic hypercortisolism, diagnosis of corticotropin dependency, and the differential diagnosis of corticotropin-dependent Cushing's syndrome. The use of a variety of baseline endocrine values, dynamic endocrine testing, and invasive procedures leads to the correct diagnosis in the majority of patients with ectopic POMC syndrome. Diagnostic imaging, including conventional radiological techniques and somatostatin receptor scintigraphy, aids in the correct localization and eventual treatment of ectopic POMC production.     

Effect of excess endogenous androgens on bone density in young women

To determine whether endogenous androgens influence bone density in young women, we studied 27 normal women and 19 women with androgen excess, as defined by increased serum bioavailable testosterone (bio T) concentrations. The women ranged from 21-48 yr of age. The 2 groups were comparable with respect to age, anthropomorphic measures, nutrition, gynecological history, and serum cortisol and estradiol levels. Trabecular (lumbar) and cortical (radial) bone density were quantitated by computerized tomography and single photon absorptiometry, respectively. Serum obtained during the follicular phase of the cycle was assayed for bio T, total T, dehydroepiandrosterone sulfate, androstenedione (Adione), and 3 alpha-androstanediol glucuronide (3-Adiol-G). Trabecular bone density was significantly higher in the androgen excess group [172 +/- 7 (+/- SE) vs. 153 +/- 5 mg/mL; P = 0.03]; controlling for serum Adione (but not for serum bio T, total T, dehydroepiandrosterone sulfate, or 3 alpha-androstanediol glucuronide, or 3-Adiol-G) abolished this difference. Similarly, serum Adione correlated more strongly than the other androgens with trabecular bone density (r = 0.31; P = 0.03). Average cortical bone density was not higher in the androgen excess group (0.740 +/- 0.014 vs. 0.722 +/- 0.008 g/cm2; P = 0.27). Among the 27 normal women, cortical density was correlated to serum bio T (r = 0.47; P = 0.01) and total T (r = 0.53; P = 0.004), but not to the other androgens. We conclude that supraphysiological levels of endogenous androgens are associated with increased trabecular bone density in young women. Serum Adione appeared to be the best marker for the impact of androgen on trabecular density. Among normal women, cortical bone density was related to serum T.     

Effect of N-terminal portion of pro-opiomelanocortin on aldosterone release by human adrenal adenoma in vitro

An adrenal cortex adenoma, surgically removed from a female patient with primary aldosteronism, was used to examine the effect of ACTH, angiotensin II, gamma 3-MSH, and the N-terminal fragment of pro-opiomelanocortin purified from porcine anterior pituitaries on aldosterone release in vitro. Primary cultures of tumor cells were incubated as a monolayer in a 96-well microtitration plate and the aldosterone release was measured in the incubation medium after 2 h of incubation in the presence of absence of different concentrations of the peptides. On a molar basis, the N-terminal portion of pro-opiomelanocortin seems to have the highest activity of all of the peptides assayed.     

Effect of luteinization stimulator and androgens on maturation of porcine granulosa cells

Luteinization stimulator (LS), an intrafollicular compound of preovulatory (5-8 mm) follicles, enhanced both basal and gonadotropins-stimulated production of progesterone (P4) by immature granulosa cells. The activity of LS was found in cell conditioned media (CM) obtained after the 3-day cultivation of preovulatory granulosa cells. Influence of testosterone, androstenedione and dihydrotestosterone on LS-enhanced P4 secretion was tested in culture of granulosa cells isolated from small follicles (1-3 mm). Small porcine granulosa cells were cultivated with or without LS in the presence of testosterone, androstenedione and dihydrotestosterone in concentration 10-10, 10-8 and 10-6 mol.l-1. In the absence of LS, P4 production in the media with androgens was not significantly different from controls. LS alone significantly enhanced progesterone production by SGC. Androgens present in the culture media together with LS decreased a stimulatory influence of LS on P4 secretion. These data suggest a possible modulation of granulosa cells maturation by androgens.     

Effect of androgens on prolactin (PRL) release in humans.

In order to evaluate whether androgens were able to affect PRL release, testosterone and dihydrotestosterone were injected intramuscularly in male and female subjects. PRL blood levels were not modified by testosterone either in healthy males or in amenorrhoeic women, and PRL release in males proved unaffected by dihydrotestosterone at the dose used.