ADRENORECEPTORS IN THE HUMAN PENIS

Abstract

Adrenaline [epinephrine], noradrenaline [norepinephrine] and phenylephrine caused contraction of the corpus cavernosum muscle of the human penis. These sympathomimetic amines did not produce inhibitory effects even in the presence of the .alpha.-adrenoreceptor blocker, phentolamine. The effect of dopamine was similar to that produced by these 3 sympathomimetic amines. Higher doses of isoprenaline and salbutamol also contracted this preparation. Cocaine and guanethidine enhanced the motor response to adrenaline, noradrenaline and phenylephrine while the action of dopamine was blocked by these 2 drugs. The motor responses to adrenaline, noradrenaline and phenylephrine was antagonized by phentolamine and often potentiated by the .beta.-adrenoreceptor blocking drug, propranolol. The contractions produced by high doses of salbutamol and isoprenaline were also abolished by phentolamine. The motor response to sympathomimetic amines is the result of activation of .alpha.-adrenoreceptors in the corpus cavernosum muscle. At low doses, isoprenaline and salbutamol relaxed the corpus cavernosum muscle strip. The inhibitory action was blocked by low concentrations of propranolol but not by practolol (.beta.1-adrenoreceptor antagonist) and butoxamine (.beta.2-adrenoreceptor antagonist). .beta.-adrenoreceptors are present in the corpus cavernosum muscle but are unlikely to be either .beta.1 or .beta.2 type. The existence of a 3rd type of .beta.-adrenoreceptor is suggested.