Systemic and cavernosal plasma levels of endothelin (1-21) during different penile conditions in healthy males and patients with erectile dysfunction.

Abstract

The role of the sympathetic adrenergic nerves in mediating the 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. The peptide endothelin-l (ET-1) may be one of the factors contributing to such a control. Moreover, it has been speculated that ET-1 might be involved in the pathophysiology of penile erection. The present study was undertaken to determine whether or not there is a difference in the courses of ET-1/-2 plasma levels recorded in systemic and cavernosal blood taken from healthy males and patients with erectile dysfunction (ED) during different penile conditions (flaccidity, tumescence/rigidity, detumescence). The study groups comprised 33 healthy adult males and 25 patients. The subjects were exposed to visual and tactile erotic stimuli in order to elicit penile tumescence and, in the group of healthy volunteers, rigidity. Whole blood was aspirated from the corpus cavernosum and the cubital vein, and ET- 1/-2 was determined in plasma aliquots by means of an enzyme-linked immunosorbent assay (ELISA). Mean systemic and cavernosal plasma levels of ET- 1/-2 in blood samples obtained from the volunteers was 0.2-0.7 fmol/ml. In the healthy males, no changes in ET-1/-2 levels were observed in the systemic and cavernosal blood during penile tumescence, rigidity and detumescence. In the patients, mean plasma ET-1/-2 levels during penile flaccidity and detumescence were found to be higher in the systemic circulation than in the cavernosal blood (flaccidity 0.52 +/- 0.38 fmol/ml vs 0.48 +/- 0.46 fmol/ml, respectively: detumescence 0.53 +/- 0.33 fmol/ml vs 0.27 +/- 0.11 fmol/ ml, respectively). No differences in the plasma courses of ET-1/-2 were found between patients with an organogenic and those with a psychogenic aetiology of ED. During detumescence, the mean ET-1/-2 level was lower in the cavernosal blood taken from the patients than in the samples obtained from the healthy males. Our study revealed a difference in the profiles of ET-l/-2 in the cavernosal blood of healthy subjects and patients with erectile dysfunction. Nevertheless, since this difference seemed to be of no physiological significance, our findings contradict the hypothesis of the ultimate importance of ET-1 in the control of penile flaccidity and detumescence and do not support speculations regarding the involvement of ET-1 in the pathophysiology of erectile dysfunction.