Sympathetic inhibition of papaverine induced erection

We studied the effect of neurostimulation of the lumbar sympathetic trunks on papaverine-induced penile erection in dogs and monkeys. The mean of 124 cm. H2O intracavernous pressure after papaverine injection was reduced under sympathetic trunk stimulation to 40.6 cm. H2O within a mean of 39 sec. In addition the flow of the internal pudendal artery was reduced indicating a decrease of the inflow to the penis. After the sympathetic stimulation was terminated, the intracavernous pressure increased again to the same level as before. This pressure recovery time was delayed after several sympathetic stimulations from 134 sec. (5 min. after papaverine injection) to at least 362 sec. (45 minutes after papaverine injection). Stimulation of the inferior hypogastric plexus had no effect on the intracavernous pressure. The neurostimulation range (3-4V; 20 Hz) was most effective in reducing the papaverine action on penile smooth muscles. The effect of sympathetic trunk stimulation seems to antagonize the relaxing action of papaverine on the cavernous smooth muscles and the cavernous arterioles. Our results imply that high sympathetic tone in some patients with psychogenic impotence may explain their poor response to intracavernous injection of papaverine.