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 p eptide (anti-VIP) antisera on electrically induced penile erection wer e studied in 18 male mongrel dogs. Electrical pulse stimulation (4 V, 4 milliseconds, 40 Hz) of the pelvic splanchnic nerve consistently pro duced penile erection (''electroerection''). Using this erection model , effects of anti-VIP serum were evaluated with regard to the peak int racorporeal pressure during electroerection. Pretreatment of the anima ls with repetitive intracorporeal infusion of anti-VIP rabbit serum co mpletely abolished the electroerection in nine dogs, partially suppres sed it (P < 0.01) in five, and was without effects in four. In contras t, control treatment of the same 18 dogs with normal rabbit serum was totally ineffective. In six dogs in which anti-VIP serum failed to pro duce a complete suppression of electroerection, 0.5 mg atropine sulfat e 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 a ny significant degree. To five of these six dogs with positive respons e to the combination treatment with anti-VIP serum and atropine, prazo sin HCl was added i.v. It was found that prazosin HCl reversed the att enuation of electroerection produced by combined anti-VIP serum and at ropine. Prazosin did not affect the intracorporeal pressure when admin istered following anti-VIP serum. These results suggest that VIP plays a role as a humoral mediator involved in penile erection and that the re is a synergistic interaction between VIP and acetylcholine. Also it appears that the effect of acetylcholine but not that of VIP is media ted by the alpha-1 adrenergic mechanism.