Comparison of the responses to drugs acting on adrenoreceptors and muscarinic receptors in human isolated corpus cavernosum and cavernous artery.

Abstract

The contractile and relaxant effects of drugs which interact with adreno- and muscarinic receptors were investigated in isolated tissue from the human corpus cavernosum urethrae (CC) and the cavernous artery (Acc). Isolated CC preparations were contracted in a concentration-dependent fashion by noradrenaline (NA), phenylephrine and clonidine in the mentioned order of potency. Prazosin was 300 times more active than rauwolscine in inhibiting NA-induced contractions. In segments of the isolated Acc, clonidine was more potent than NA and phenylephrine, and prazosin and rauwolscine were about equieffective in inhibiting NA-induced contractions. Prazosin was more effective than rauwolscine in CC strips, and rauwolscine more effective than prazosin in Acc segments in inhibiting the noradrenergically mediated part of electrically induced contractions. Isoprenaline, prenalterol and procaterol each relaxed NA-contracted CC preparations in a concentration-dependent way; this effect was blocked by propranolol. Isoprenaline had no relaxant action in Acc segments. Neither acetylcholine (ACh) nor carbachol produced contraction in CC and Acc preparations. ACh, but particularly carbachol, had potent relaxant effects in NA-contracted CC preparations. This effect of ACh and carbachol was blocked by scopolamine. Relaxant, but less potent effects of the muscarinic receptor agonists were found in the Acc segments. It is suggested that there are important differences between penile arteries and erectile tissue proper in the response to adrenoreceptor and muscarinic receptor active drugs. The contractile effect of NA seems to be mediated mainly by alpha 1-adrenoreceptors in the CC and by alpha 2-adrenoreceptors in the Acc. It cannot be excluded that muscarinic receptor-mediated relaxation of NA-contracted CC preparations can be of importance for penile tumescence and erection.