La testosterona inhibe las respuestas contráctiles del agonista adrenérgico alpha1, fenilefrina, asociadas con la liberación de calcio intracelular en la aorta de rata / Testosterone inhibits the contractile responses to phenylephrine associated with the release of intracellular calcium in rat aorta

Utilizando segmentos de aorta de rata sin endotelio inmersos en solución sin Ca2+, evaluamos la capacidad de la testosterona para modificar el efecto contráctil del agonista adrenérgico fenilefrina, así como el incremento en el tono de reposo (ITR) asociado con la entrada capacitativa de calcio por el sarcoplasma. La testosterona [10-5–10- 4 M] inhibió significativamente la contracción activada por la fenilefrina [10-6 M] y el ITR. Estos efectos no fueron modificados con cicloheximida [10-5 M] (inhibidor de la síntesis protéica), flutamida [10-5 M] (antagonista de receptores androgénicos), o aminoglutetimida [10-5 M] (inhibidor de la citocromo P450 aromatasa). La testosterona también inhibió las respuestas contráctiles de la serotonina [10-5 M], pero no de la cafeína [10-2 M]. Además, la testosterona inhibió las contracciones del ácido ciclopiazónico [10-6 M] y de la ryanodina [10- 5 M] asociadas con el ingreso capacitativo de Ca2+ mediante canales de Ca2+ tipo no L. Estos datos sugieren que la testosterona interfiere con la vía de transducción de los receptores acoplados a proteínas Gq- 11, e inhibe la entrada capacitativa de Ca2+ a través de canales de Ca2+ tipo L y tipo no L; los efectos son no genómicos, independientes de receptores androgénicos, y de la conversión testosterona en estrógenos.

Using endothelium-denuded rat aortic rings incubated in Ca2+ -free solution, we assessed the ability of testosterone to influence the contractile effect of phenylephrine, and the increase in resting tone (IRT) associated with Ca2+ ability to cross the plasma membrane. The addition of testosterone [10(-5)-10(-4) 5 min before phenylephrine [10(-6) M], inhibited both phenylephrine-induced contraction and IRT. These changes were not affected by cycloheximide (10(-5) M; a protein synthesis inhibitor of), flutamide (10(-5) M; an androgenic receptor antagonist), or by adding aminoglutethimide (10(-5) M; an aromatase inhibitor). Testosterone also blocked the contractile response to serotonin [10(-5) M] but not to caffeine [10(-2) M]. On the other hand, testosterone inhibited the contractile responses to cyclopiazonic acid (10(-6) M; a selective Ca2+ -ATPase inhibitor) or ryanodine (10(-5 M; an activator of sarcoplasmic reticulum Ca2+ -release channels) associated with capacitative Ca2+ influx through non-L-type Ca2+ channels. These data suggest that by acting on the cellular membrane, testosterone interferes with the signal transduction pathway of G(q-11) protein-coupled receptors, and inhibits capacitative Ca2+ influx through both L-type and non-L-type Ca2+ channels. These effects are non-genomic, non-mediated by the intracellular androgen receptor, and not due to the conversion of testosterone to estrogens.

Pharmacological evidence that cromakalim inhibits Ca2+ release from intracellular stores in porcine coronary artery

In the present study, it was aimed to further identify the intracellular action mechanism of cromakalim and levcromakaliin in the porcine coronary artery. In intact porcine coronary arterial strips loaded with fura-2/AM, acetylcholine caused an increase in intracellular free Ca2+ ((Ca2+)-i) in association with a contraction in a concentration-dependent manner. Cromakalim (1 micrometer) caused a reduction in acetylcholine-induced increased (Ca2+)-i not only in the normal physiological salt solution (PSS) but also in Ca2+ -free PSS (containing 1mM EGTA). In the skinned strips prepared by exposure of tissue to 20 micrometer beta-escin, inositol 1,4,5-trisphosphate (IP-3) evoked an increase in (Ca2+)-i but it was without effect on the intact strips. The IP-3-induced increase in (Ca2+)-i was inhibited by cromakalim by 78% and levcromakalim by 59% (1 micrometer, each). Pretreatment with glibenclamide (a blocker of ATP-sensitive K+ channels, 10 micrometer and apamin (a blocker of small conductance Ca2+/-activated K+ channels, 1 micrometer strongly blocked the effect of cromakalim and levcromakalim. However, charybdotoxin (a blocker of large conductance Ca2+ -activated K+ channels, 1-micrometer) was without effect. In addition, cromakalim inhibited the GTP-gamma-S (100 micrometer, nonhydrolysable analogue of GTP)-induced increase in (Ca2+)-i. Based on these results, it is suggested that cromakalim and levcromakalim exert a potent vasorelaxation, in part, by acting on the K+ channels of the intracellular sites (e.g., sarcoplasmic reticulum membrane), thereby, resulting in decrease in release of Ca2+ from the intracellular storage site.