Systemic and cavernous plasma levels of endothelin 1 in healthy males during different functional conditions of the penis

The role of the sympathetic adrenergic nerves in mediating the constant ton e of penile flaccidity and returning the erect penis to its flaccid state i s fairly well established. However, it is not yet known whether additional nonadrenergic transmitters might be involved in this process. Endothelin 1 (ET-1), a 21-amino-acid peptide with potent and long-lasting vasoconstricto r activity, may be one of the factors contributing to such control. The pre sent study was undertaken to determine whether plasma levels of ET-1 change d during flaccidity: tumescence, rigidity, and detumescence. We determined plasma levels of ET-1 in the peripheral and cavernosal blood of 32 potent a dult male volunteers, in whom penile tumescence and erection were elicited by exposure to visual and tactile erotic stimuli. Whole blood was aspirated from the corpus cavernosum and the cubital vein, and ET-1 was quantified i n plasma aliquots obtained from the blood samples. Using the organ bath tec hnique, we evaluated the contractile effects of ET-1 and norepinephrine (NE ) on isolated human corpus cavernosum musculature. No significant change in ET-1 levels was observed in the peripheral or cavernosal blood in the proc ess of developing erection, rigidity, or detumescence. The mean plasma leve l of ET-1 was 0.2-0.7 fmol/ml. In the organ bath, ET-1 elicited concentrati on-dependent contractions of isolated human corpus cavernosum, which were m uch more pronounced than those evoked by the adrenergic agonist NE. Our dat a indicate that despite the in vitro efficacy of ET-1 in stimulating contra ctile activity in isolated human cavernous smooth muscle, the peptide may n ot be of ultimate importance for the mechanism of flaccidity and detumescen ce in healthy males. Nevertheless, the exact role of ETs in the control of penile smooth muscle tone remains to be established.