Reduction of sympathetic influences on penile erection by phentolamine.

The lumbosacral sympathetic trunks seem to play a major role in penile detumescence. In animal experiments an erection induced by cavernous nerve stimulation can be abolished by neurostimulation of the canine sympathetic trunks. This canine experiment was designed to study the possible reduction of the sympathetic effect by intravenous injection of phentolamine. The aborted erection by sympathetic trunks stimulation was partially antagonized by phentolamine. The arterial flow to the penis as well as the intracavernous pressure were elevated by this drug. As an expected side effect the systemic arterial blood pressure decreased by 4-14 cm H2O after phentolamine injection.