Penile erections induced by vasoactive intestinal peptide and sodium nitroprusside

The use of vasoactive intestinal peptide (VIP), sodium nitroprusside (SNP), and the reference combination of papaverine, prostaglandin E1, and phentolamine was studied in 22 adult cats. The maximal erectile response (intracavernous pressure, penile length, and rigidity) was produced by intracavernous injection of a combination of 1.65 mg papaverine, 0.5 micrograms PGE1, and 25 micrograms phentolamine. This combination was considered as "control" in order to compare the effect of other agents. VIP and SNP increased the intracavernous pressure and caused erection in a dose-dependent manner with a maximal response obtained with 5 micrograms VIP or 10 micrograms SNP. The duration of peak erection and the total duration of drug effect were significantly shorter with VIP and SNP than with the reference combination (P < 0.01). Epinephrine (30 micrograms) reversed the effects of SNP and significantly shortened the duration of peak action and total effect (P < 0.05). This study supports the use of an in vivo feline model for the evaluation of vasoactive agents and demonstrates that the intracavernous injection of either VIP or SNP can induce penile erection in the adult cat.