Involvement of vasoactive intestinal peptide (VIP) as a humoral mediator of penile erectile function in the dog.

The effects of intracorporeal infusion of anti-vasoactive intestinal peptide (anti-VIP) antisera on electrically induced penile erection were studied in 18 male mongrel dogs. Electrical pulse stimulation (4 V, 4 milliseconds, 40 Hz) of the pelvic splanchnic nerve consistently produced penile erection ("electroerection"). Using this erection model, effects of anti-VIP serum were evaluated with regard to the peak intracorporeal pressure during electroerection. Pretreatment of the animals with repetitive intracorporeal infusion of anti-VIP rabbit serum completely abolished the electroerection in nine dogs, partially suppressed it (P < 0.01) in five, and was without effects in four. In contrast, control treatment of the same 18 dogs with normal rabbit serum was totally ineffective. In six dogs in which anti-VIP serum failed to produce a complete suppression of electroerection, 0.5 mg atropine sulfate was additionally given i.v. All six dogs exhibited significant (P < 0.01) suppression of the peak intracorporeal pressure after atropine. However atropine alone did not affect the intracorporeal pressure to any significant degree. To five of these six dogs with positive response to the combination treatment with anti-VIP serum and atropine, prazosin HCl was added i.v. It was found that prazosin HCl reversed the attenuation of electroerection produced by combined anti-VIP serum and atropine. Prazosin did not affect the intracorporeal pressure when administered following anti-VIP serum. These results suggest that VIP plays a role as a humoral mediator involved in penile erection and that there is a synergistic interaction between VIP and acetylcholine. Also it appears that the effect of acetylcholine but not that of VIP is mediated by the alpha-1 adrenergic mechanism.