ABSTRACT
Histamine is supposed to play an important role to the penile erection mechanisms. We reported that histamine induced a dose-dependent contraction in rabbit corpus cavernosum tissue but in human the exact effect and mechanisms are not established. To investigate the effects of histamine on the corpus cavernosum tissue and the intracellular signal transduction mechanisms, we have studied on the human corpus cavernosum using organ bath and the following results were obtained. 1. Histamine produced no contraction in human corpus cavernosum tissue. 2. In the precontracted tissue by phenylephrine histamine produced dose-dependent relaxation (ED50=2.70x0.00001mol). 3. Histamine-induced relaxation was not dependent on endothelium 4. Histamine-induced relaxation was not affected by administration of pheniramine maleate(0.00001mol), but abolished by cimetidine(0.00001 mol). 5. In the precontracted tissue by phenylephrine histamine produced no relaxation, but pheniramine maleate produced significant relaxation in precontracted tissue. 6. Histamine-induced relaxation was not affected by methylene blue(0.000 01mol), a guanylate cyclase inhibitor, but in a precontracted strip by phenylephrine.forskolin, an adenylate cyclase activator, produced dose-dependent relaxation (ED50=9.34x0.0000001mol). It is concluded that in human, histamine induced dose-dependent relaxation, independent from endothelium, mediated by H2-receptors and cAMP as an intracellular second messenger. The H1-receptors were supposed to be associated with contraction, but distributed in scanty density. By the results of this study, it is supposed that histamine or pheniramine maleate could be used as a drug of intracavernosal injection therapy, but in vivo study and/or in vitro study under electrical stimulation must be preceded.