Volume 47 (2000) Issue 4 Pages 417-428
The effect of T3 on basal and LH mediated synthesis and secretion of testosterone and oestradiol by puberal rat Leydig cells was studied in vitro. Percoll gradient purified Leydig cells (1×103) were cultured for 48 hours at 34°C in a medium containing a range of 5-400ng/mL concentration of T3 or ovine LH after 24 hours initial culture at 37°C. T3 increased testosterone and oestradiol secretions in a dose dependent manner which reached the saturation point with 50ng dose. While the minimum effective dose of T3 (25ng) potentiated the stimulatory effect of the minimum effective dose of LH (25ng) on testosterone secretion, it suppressed the effect of the saturation dose of LH (100ng). Fifty ng T3 quelled the stimulatory effect of either dose of LH. Both doses of T3 increased oestradiol secretion, irrespective of the dose of LH. Addition of androstenedione (500ng/mL) to the culture medium enhanced 25ng T3 induced testosterone and oestradiol secretions. While androstenedione potentiated the stimulatory effect of T3 (25ng) on LH (25ng) induced testosterone and oestradiol secretions, it reversed the inhibitory effect of 50ng T3 on LH mediated testosterone secretion which was accompanied by a decrease in oestradiol secretion. Puromycin (35μg/mL) suppressed the stimulatory effect of T3 on basal and LH mediated testosterone and oestradiol production. Taken together, the present results indicate a direct stimulatory effects of T3 on basal production of testosterone and oestradiol by Leydig cells and its modulatory effect on LH mediated steroidogenic activity varies depending upon the intensity of LH stimuli.