Stimulatory effects of alpha-hANP on testosterone secretion in man

Several recent observations suggest that atrial natriuretic peptides (ANP) can modulate steroidogenesis in isolated rat Leydig cells. At present, it is unknown whether ANP influence human testicular steroidogenesis. We therefore evaluated the effects of alpha-human ANP (hANP) administration on testosterone plasma levels in peripheral and internal spermatic venous blood of young men (catheterized for contrast study of varicocele). Six subjects were injected with 100 micrograms alpha-hANP in the cubital vein. Six different patients similarly received 50 micrograms LHRH. Three controls received 2 ml saline. Plasma LH, FSH, and testosterone were then determined 15 min before, at time of injection, and 15, 30, 45, and 60 min thereafter in spermatic vein and peripheral venous blood, as well as at 120 min in peripheral blood. LHRH--induced LH increase was followed by a marked increase of spermatic vein testosterone concentrations, but the peripheral testosterone concentration did not increase. Similarly, alpha-hANP administration did not affect peripheral testosterone and LH concentrations, but significantly increased spermatic vein testosterone levels (P less than 0.01). Our findings demonstrate that alpha-hANP exerts its stimulatory effect on testicular steroidogenesis in man without modifying gonadotropin secretion, suggesting that alpha-hANP may directly influence Leydig cell function.