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

Introduction and objectives. The role of the sympathetic adrenergic nerves in mediating a constant tone of penile flaccidity and returning the erect penis to its flaccid state is fairly well established. However, it is not yet known whether additional nonadrenergic transmitters are involved in this process. Endothelin-1 (ET-1), a peptide with vasoconstrictor activity, may be one of the factors contributing to such control. The present study was undertaken to determine whether or not plasma levels of ET-1 change in the cavernous and systemic blood during flaccidity, tumescence, rigidity and detumescence.

Patients and methods. We determined plasma levels of ET-1 in the peripheral and cavernosal blood of 32 healthy, potent 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 corpora cavernosa and the cubital vein, and ET-1 was quantified in plasma aliquots by means of an enzyme immunoassay (ET-1 ELISA, Biomedica GesmbH, Vienna, Austria).

Results. The mean plasma level of ET-1 in the systemic and cavernous blood was 0.2-0.7 fmol^-1. No significant changes were detected in the ET-1 levels, either in the peripheral or in the cavernous blood in the phases of penile flaccidity, tumescence, rigidity and detumescence. Moreover, there were no significant differences in the ET-1 levels of the cavernous and the peripheral blood in the respective stages. It was only during rigidity that a moderately significant difference was found in the ET-1 levels of the systemic and penile blood. The mean systemic ET-1 level was higher than that registered in the cavernous blood (P = 0.046).

Conclusion. Our data indicate that ET-1 may not be of ultimate importance for the mechanism of flaccidity and detumescence in healthy males. Nevertheless, the exact role of ETs in the control of penile smooth muscle tone and in the pathophysiology of erectile dysfunction remains to be established. Our data provide the basis for further investigations on the plasma profile of ET-1 in a group of patients with erectile dysfunction.

Funding. This study was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG).