THE ROLE OF HISTAMINE IN HUMAN PENILE ERECTION

Objective To investigate the relaxant action of histamine on human cor pus cavernosum in vitro and the erectile response caused by the intrac avernous injection of histamine in patients with psychogenic impotence . Patients and methods Human corpus cavernosum (HCC) tissue was cut in to strips of approximately 2 cm and suspended in a cascade bioassay. T he strips were then superfused with oxygenated and warmed Krebs soluti on and precontracted with noradrenaline (3 mu M). Glyceryl trinitrate, acetylcholine and histamine were injected as a single bolus in the ab sence or in the presence of mepyramine and cimetidine. For the in vivo studies, histamine (30-60 mu g) was injected intracavernously as a si ngle bolus into the right corpus cavernosum 1 cm from the balamo-prepu tial sulcus. Similar protocols were carried out for papaverine (50 mg) . The erectile response was divided into four grades: no response, tum escence, partial and full erection. Results In vitro studies demonstra ted that histamine (3-100 mu g) caused dose-dependent relaxation of th e HCC strips which was significantly inhibited by cimetidine (5-10 mu M). The histamine H-1 receptor antagonist mepyramine (1 mu M) potentia ted histamine-induced relaxation. The co-infusion of both mepyramine a nd cimetidine did not abolish histamine-induced relaxation. When injec ted intracavernously in humans, histamine (30 mu g) caused full erecti on in 13% of the patients, whereas 87% had partial erection or tumesce nce. A higher dose of histamine (60 mu g) caused full erection in 26% of the patients and 74% had partial erection or tumescence. Papaverine induced full erection in the majority of patients (66%). In contrast to papaverine, the duration of erection induced by histamine was marke dly shorter (mean 200 and 6.5 min, respectively). The penile erections induced by papaverine were associated with complications such as pain , haematoma and priapism. Histamine did not induce any complications. Treatment of eight male patients with psychogenic impotence with the h istamine H-1 receptor antagonist astemizol (10 mg orally once daily fo r 1 week) did not affect histamine-induced erectile responses. Conclus ion These results indicate that histamine may play a role in human pen ile erection. The erection-promoting action of histamine is probably d ue to H-2 receptor activation, although another histamine receptor, po ssibly H-3, also seems to be involved. This study suggests that histam ine could be a valuable tool in the diagnosis of erectile dysfunction.