The effect of gene transfer of plasmids expressing Vcsa1 or hSlo, or direct intracorporal injection of Sialorphin on erectile function in orchiectomized animals as determined by intracorporal pressure/blood pressure (ICP/BP) response following stimulation of the cavernous nerve. Four groups of five animals each were orchiectomized and injected intracorporally with either 100 μg pVAX-hSlo or pVAX-Vcsa1 or pVAX (control) for one week, or 100 μg Sialorphin for 2 hours prior to the determination of ICP/BP. The ICP/BP was determined at 4 levels of cavernous nerve stimulation (0, 2, 6 and 10 mA). Bars represent the average ICP/BP measurement from 5 animals, and the error bars the standard error of the mean. *=Significantly different ICP/BP ratio of treated to the control animals (P < 0.05).