Effect of vasoactive intestinal peptide and acetylcholine on penile erection in the rat in vivo

We investigated the effect of vasoactive intestinal peptide (VIP) and its combination with acetylcholine (ACh) on the erectile response in 52 adults rats. Intracavernous injection of VIP (10(-8) to 10(-5)M, ACh (10(-9) to 10(-5), or a combination of VIP (10(-7) to 10(-5) with ACh (10(-6 M) additively enhanced that erection but did not lead to a full erection. VIP-antagonist (10(-9) to 10(-5 M), as well as atropine alone (10 (-7) to 10(-5 M), partially suppressed full erection induced by cavernous nerve stimulation (1 Hz, 3-6 V) in a dose-dependent manner, and the combination of VIP-antagonist (10(-9) to 10(-5 M) with atropine (10(-6 M) showed an additive effect. The results indicate that although VIP as well as ACh in involved in penile erection, they are not likely to be principal neurotransmitters. Their clinical application in the treatment of impotence may be confined to use in conjunction with another vasoactive agent.