EFFECTS OF ENDOTHELIN-1 ON THE RAT TESTICULAR VASCULATURE

Endothelin-1 (ET-1), a well-known vasoconstrictor substance, is presen t in the testis but its functional role is unknown. The present study was undertaken to elucidate whether ET-1 may influence testicular bloo d flow. ET-1 (0.1, 1, 10, 100 ng), an ET(A) antagonist (BQ123; 0.01, 1 , 100 mu g), or saline were administered by intratesticular injections (0.1 ml) in adult rats. The effect on testicular blood flow was monit ored using a laser Doppler flowmeter. The localization of immunoreacti ve ET-1 (irET-1) was studied by immunohistochemistry and the testicula r irET-1 concentration was measured in normal and human chorionic gona dotrophin (hCG)-treated rats using a radioimmunoassay. ET-1 injection, in a dose-related way acutely decreased testicular blood flow and thi s effect was blocked by an ET(A) antagonist. The antagonist itself did not, however, influence testicular blood flow. Accumulation of polymo rphonuclear leukocytes was observed in testicular venules 2 hours afte r ET-1 injection. Immunoreactive ET-1 was observed in Leydig, Sertoli, and endothelial cells. The testicular irET-1 content was increased 2- fold by hCG stimulation but local injection of the ET-1 antagonist did not influence testicular blood Row in hCG-treated rats. The present s tudy suggests that ET-1 could be a hormonally regulated and locally pr oduced modulator of testicular blood flow and microcirculation.