PARTICIPATION OF VASOACTIVE INTESTINAL POLYPEPTIDE (VIP) AS A HUMORALMEDIATOR IN THE ERECTILE RESPONSE OF CANINE CORPUS CAVERNOSUM PENIS

The ability of anti-vasoactive intestinal peptide (anti-VIP) serum to suppress the electrically induced relaxation of the corpus cavernosum was evaluated in vitro to define the role of VIP in penile erection. S trips of canine corpora cavernosa were placed in 5-ml organ chambers c ontaining oxygenated Krebs-Ringer solution. They were stretched and fi xed in place at both ends and pretreated with 2 x 10(-7) M noradrenali ne (NA). NA was given to produce an optimal state of isometric smooth muscle contraction so that subsequent electrical field stimulation (EF S) could induce a good range of measurable relaxation response. This r esponse was deemed to be an in vitro representation of penile erection . After NA treatment the cavernous tension rose markedly by 2-2.5 g; i t then declined by up to 1-1.2 g upon EFS. Anti-VIP serum (1:16) or at ropine sulfate (10(-6) M) was added at various time points between NA administration and EFS. When anti-VIP serum was administered, subseque nt EFS-induced relaxation was attenuated by 20%-55% compared to the co ntrol EFS treatments. The degree of attenuation depended upon the freq uency of EFS applied, being 20.6% +/- 4.0% at 20 Hz and 54.7% +/- 6.3% at 2 Hz. Atropine administered additionally following anti-VIP serum produced no further attenuation. However, atropine alone was capable o f producing up to 23.7% +/- 3.5% attenuation. When anti-VIP serum was administered following atropine, the degree of attenuation that ensure d was the sum of the attenuations produced by each of the two substanc es independently. These results indicated that both VIP and acetylchol ine were involved in the EFS-induced erectile response, the contributi on of the former being greater than that of the latter. A considerable portion of the EFS-induced cavernous relaxation, however, appeared to be dependent on factors other than VIP and acetylcholine.