Stimulation of Leydig cell function by a polypeptide present in testicular interstitial fluid.

Rat testicular interstitial fluid (IF) contains a polypeptide factor(s) which when added to Percoll-purified rat Leydig cells in vitro, enhances both basal and hCG-stimulated production of testosterone in a dose-dependent manner. To assess the possible physiological significance of this factor(s), its levels in testicular IF from individual rats were assessed following the suppression of intratesticular levels of testosterone by either (a) treatment with anti-LH, (b) induction of unilateral cryptorchidism, or (c) treatment with ethane-1,2-dimethane sulphonate (EDS). These treatments suppressed testosterone levels in IF by 80 to 99% and in each instance levels of the IF-factor were increased. This increase occurred as early as 5h after anti-LH treatment, but restoration of normal intratesticular levels of testosterone at 20-40 h after anti-LH treatment by testosterone injection failed to normalize levels of the IF-factor. In contrast, injection of LH into normal rats raised IF testosterone to supranormal levels and this was associated with a reduction in levels of the IF-factor, and similar effects of hCG were observed in rats pretreated with anti-LH. Therefore, whilst these studies suggest that the IF-factor(s) may be of physiological importance, its local regulation does not appear to involve a straightforward negative feedback control by testosterone.