Penile response to intracavernosal vasoactive intestinal polypeptide alone and in combination with other vasoactive agents.

Intracavernosally injected vasoactive intestinal polypeptide (VIP) (2 micrograms and 4 micrograms) resulted in penile tumescence even in men with predominantly organic impotence. Papaverine and phentolamine were successful in inducing erections in all subjects studied but the addition of VIP to this combination improved the erectile response further. A combination of papaverine and VIP produced penile rigidity similar to that with papaverine and phentolamine. While intracavernosal VIP alone produced disappointing penile responses, its combination with papaverine potentiated the response to this drug, probably by increasing venous outflow resistance.