Systemic and cavernous plasma levels of vasoactive intestinal polypeptide during sexual arousal in healthy males

Results from basic research scrutiny indicate a role for non-adrenergic, non-cholinergic transmitters, among which there are various peptides, in the physiology of normal male sexual function. Nevertheless, it is not yet known which particular peptides are essentially involved in maintaining sexual arousal and regulating penile tumescence and rigidity in adult males. Vasoactive intestinal polypeptide (VIP), a peptide with smooth muscle relaxing properties, is considered to be one of the factors that contributes to such control. The present study was performed to evaluate the significance of VIP in normal male sexual function. We determined the plasma levels of VIP in the systemic and cavernous blood of 54 healthy adult male volunteers, who were exposed to visual and tactile erotic stimuli in order to elicit penile tumescence and erection. Whole blood was aspirated from the corpus cavernosum and the cubital vein during penile flaccidity, tumescence, rigidity and detumescence, and VIP was quantified in plasma aliquots by means of a radioimmunoassay. Of the 54 volunteers, 16 were permitted to masturbate and ejaculate, and blood was then again withdrawn from the cavernous meshwork and the cubital vein in order to measure VIP. All VIP levels were registered within the normal physiological range from 3.0-30 pmol/l. No increase in median VIP plasma levels was observed in the systemic and cavernous blood when the flaccid penis became rigid. During penile detumescence, mean cavernous VIP level increased to 11.9+/-7.8 pmol/l (baseline: 8.6+/-3.0 pmol/l), whereas VIP remained unaltered in the systemic circulation. Following ejaculation, mean VIP level in the cavernous blood was elevated to 25.3+/-10.9 pmol/l, whereas, in the systemic blood, no significant changes were registered. Our results support the hypothesis that VIP plays a functional role in the mechanism of male sexual arousal. Nevertheless, our data indicate that the peptide is not the main non-adrenergic, non-cholinergic mediator of penile tumescence and rigidity in human males.