Effect of action mechanism of vasoactive intestinal polypeptide on cavernosal smooth muscle in the rabbit penis

Kim, Young Chan; Choi, Hyung Ki; Ahn, Young Soo; Kim, Kyung Hwan

Abstract

A non-adrenergic, non-cholinergic mechanism for the penile erection has been suggested after the observation that atropine or B-receptor antagonist fails to block penile erection produced by pelvic nerve stimulation. Vasoactive intestinal polypeptide(VIP) has merged as a strong candidate for a possible non-adrenergic, non-cholinergic inhibitory transmitter in penile erection. In this study, the effect of VIP and its relationship to adrenergic or cholinergic mechanism was observed using the isolated corpus cavernosal strip from the rabbit penis, and the action mechanism of VIP was investigated with special reference to release ot endothelium dependent relaxation factor (EDRF) and the mobilization of Ca++ and K+ ions. The corpus cavernosal strip was carefully prepared from rabbit penis and was suspended in an organ bath containing 1ml of Tyrode solution maintained at 37 degrees C. The Tyrode solution was aerated with 95% oxygen and 5% carbon dioxide. One end of the cavernosal strip was attached to the bottom of the bath and the other end to the force displacement transducer(FT. 03, Grass, Quincy, Mass.). When a stable tension level of the strip had been attained, drugs were added to the organ bath and the change of been attained, drugs were added to the organ bath and the change of motility of the strip was recorded on a Polygraph (Grass Model 7, Quincy, Mass.). The results obtained were as follows: 1. VIP caused a dose-dependent relaxation of the cavernosal strip of rabbit penis. 2. VIP pretreatment had no effect on the contraction induced by a1 and a2-adrenergic agonist. 3. VIP had no synergistic effect on the relaxation produced by acetylcholine or isoproterenol. 4. Neither atropine nor propranolol had any blocking effect on the VIP-induced relaxation. 5. Methylene blue decreased the relaxation of the cavernosal strip which was induced by VIP. 6. VIP had no effect on the contraction induced by either KCl 20mM or 80mM. 7. In calcium-free high potassium solution, VIP inhibited the calcium-induced contraction. From the above results, it is suggested that VIP exerts an endothelium dependent relaxing effect on the cavernosal strip of the rabbit penis via its own receptor which is associated, in part, with the inhibition of calcium influx.