Changes in the androgen levels in asthmatic men may be associated with the severity of asthma. Androgens induce a nongenomic relaxation in airway smooth muscle, but the underlying mechanisms remain unclear. The aim of this study was to investigate the potential bronchorelaxing action of testosterone (TES) and its metabolites (5α- and 5β-dihydrotestosterone (DHT). A preventive effect on ovalbumin (OVA)-induced bronchospasm was observed in sensitized guinea pigs for each androgen. Androgens were studied in response to bronchoconstrictors: carbachol (CCh) and KCl in isolated trachea rings with and without epithelium from non-sensitized and sensitized animals as well as on OVA-induced contraction. Androgens concentration-dependently abolished the contraction in response to CCh, KCl, and OVA. There were significant differences in the sensitivity to the relaxation induced by each androgen. 5β-DHT was more potent for relaxing KCl-induced contraction, while TES and 5α-DHT were more potent for CCh- and OVA-induced contraction. No differences were found in preparations with and without epithelium or in the presence of a nitric oxide (NO) synthase inhibitor or an inhibitor of K⁺channels. These data indicate the absence of involvement of the epithelium-, NO- and K⁺channels-dependent pathway in androgen-induced relaxation. However, in dissociated tracheal myocytes loaded with the calcium-binding fluorescent dye Fura -2, physiological concentrations of androgens decreased the KCl-induced [Ca²⁺]_iincrement. 5β-DHT was the most potent at decreasing KCl-induced [Ca²⁺]_iincrement and preventing bronchospasm. We suggest that androgen-induced brochorelaxation was mediated via decreased Ca²⁺influx through L-type Ca²⁺channels but additional Ca²⁺entry blockade may be involved. Molecular changes in androgen structure may determine its preferential site of action.

Androgen vasorelaxing action is a subject of recent interest. We investigated the involvement of l-type voltage-operated Ca2+ channels (L-VOCCs), K+ channels, intracellular Ca2+ concentration ([Ca2+]i), and cAMP in the vasorelaxing effect of testosterone and 5β-dihydrotestosterone (5β-DHT) on rat thoracic aorta. Isolated aortic rings were used to study the vasorelaxing potency of testosterone and 5β-DHT on KCl- and noradrenaline-induced contractions. Patch-clamp was used to analyze androgen effects on Ca2+ inward and K+ outward currents. The fluorescence technique was used to evaluate [Ca2+]i in single myocytes; moreover, simultaneous measurements of [Ca2+]i and vascular contraction were evaluated. 5β-DHT was more potent than testosterone to relax KCl-induced contraction, but they were equipotent to relax noradrenaline contraction. l-type Ca2+ currents were blocked by nifedipine, both androgens, and an estrogen in a concentration-dependent manner, and the order of potency was: testosterone > nifedipine > 5β-DHT > 17β-estradiol. We observed that testosterone has different mechanism of action by the concentration range used: at nm concentrations it was a powerful L-VOCCs antagonist, whereas at μm concentrations it was observed that: 1) its Ca2+ antagonist property is reverted by increasing the l-type inward Ca2+ currents (Ca2+ agonist property); and 2) the [Ca2+]i and cAMP production was increased. The total K+ currents were unaffected by testosterone or 5β-DHT. The data show that 5β-DHT-induced vasorelaxation is due to its selective blockade on L-VOCCs (from nm to μm concentrations), but testosterone-induced vasorelaxation involves concentration-dependent additional mechanisms: acting as an L-VOCCs antagonist at low concentrations, and increasing [Ca2+]i and cAMP production at high concentrations.

It has long been accepted that progesterone regulates uterine contractile activity. However, little is known about the role of androgens in female physiology, and their importance and biological function on myometrial contractility so far have received limited attention. In this work, we examined the direct effect of androgens on the contractile activity of the isolated human myometrium. Myometrial biopsies were obtained, with consent, from pregnant women undergoing elective cesarean section at term. Each androgen tested (dehydroepiandrosterone, testosterone, 5α- and 5β-dihydrotestosterone, androsterone, or androstanediol) caused a concentration-dependent inhibition of spontaneous contractile activity; a relaxing effect of these androgens was also observed on the contractions induced by high potassium (KCl) solution. Interestingly, nonpregnant myometrium was also sensitive to androgen-induced relaxation. 5β-Dihydrotestosterone (5β-DHT) was dramatically more potent than the other androgens in inducing myometrial relaxation in all preparations. Relaxation response to androgens had very rapid time courses and was affected by neither the specific antiandrogen (flutamide) nor inhibitors of protein synthesis (cycloheximide) and transcription (actinomycin D), implying that androgens act through a nongenomic mechanism. Importantly, 5β-DHT significantly reduced the increase in intracellular calcium concentration associated with exposure to KCl in human myometrial smooth-muscle cells loaded with Fura-2-AM. The blockade of l-type calcium channels seems to be involved in the nongenomic relaxing action of androgens. These observations demonstrate that androgens may play a crucial role in maintaining pregnancy.

Inhibitory interactions between 5-HT subtype 3 (5-HT₃) and P2X receptors were characterized using whole cell recording techniques. Currents induced by 5-HT ( I_5-HT) and ATP ( I_ATP) were blocked by tropisetron (or ondansetron) and pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid, respectively. Currents induced by 5-HT + ATP ( I_5-HT+ATP) were only as large as the current induced by the most effective transmitter, revealing current occlusion. Occlusion was observed at membrane potentials of −60 and 0 mV (for inward currents), but it was not present at +40 mV (for outward currents). Kinetic and pharmacological properties of I_5-HT+ATPindicate that they are carried through 5-HT₃and P2X channels. Current occlusion occurred as fast as activation of I_5-HTand I_ATP, was still present in the absence of Ca²⁺or Mg²⁺, after adding staurosporine, genistein, K-252a, or N-ethylmaleimide to the pipette solution, after substituting ATP with ∝,β-methylene ATP or GTP with GTP-γ-S in the pipette, and was observed at 35°C, 23°C, and 8°C. These results are in agreement with a model that considers that 5-HT₃and P2X channels are in functional clusters and that these channels might directly inhibit each other.