Vasoactive intestinal polypeptide in relation to penile erection in the cat evoked by pelvic and hypogastric nerve stimulation.

The hemodynamics of penile erection were elucidated in the anesthetized cat by studying volumetrically determined erectile responses of the penis and penile blood flow during frequency-graded bilateral stimulation of the pelvic and the hypogastric nerves, selectively or in combination. The study also provided information on possible neurotransmitter mechanisms. The results indicated that the erectile response is mediated by both the pelvic and hypogastric nerves, operating synergistically to evoke a seemingly maximum erection. Optimum erectile responses for either nerve system were obtained at 16 Hz and threshold responses at 0.5 to one Hz. In the presence of atropine, the erectile response to selective stimulation of the pelvic and the hypogastric nerves, respectively, were clearly curtailed, suggesting a cholinergic mechanism to be partly responsible for the diversion of blood from the penile "resistance vessels" to the cavernous bodies, possibly accomplished via the opening of vessels with a shunt-like function. However, the magnitude of the erectile response to combined pelvic and hypogastric nerve stimulation seemed to be surprisingly little affected by muscarinic blockade. Selective stimulations of the pelvic and the hypogastric nerves, respectively, were both found to cause about a five-fold increase in VIP output from the penis, coordinated in time with the local blood flow increase during erection. These data suggest a VIP-ergic neurotransmitter mechanism to be involved in penile erection in the cat, possibly controlling the dilation of the penile arterial "resistance vessels."