Stimulation and inhibition by LHRH analogues of cultured rat Leydig cell function and lack of effect on mouse Leydig cells.

The effect of 2 luteinizing hormone-releasing hormone (LHRH) analogues(10-8-10-6 M) on the functional activity (testosterone and cyclic AMP production and [125I]hCG binding) of purified mouse Leydig cells in culture was examined. The analogues were found to have no significant effect on the cells over a period of 3 days. No specific binding of a labelled analogue to impure or pure mouse Leydig cells could be detected. In contrast high levels of specific binding to impure rat interstitial cells occurred. Centrifugation of the rat interstitial cells on 0-90% Percoll gradients showed that the LHRH analogue bound specifically to the active lutropin-responsive Leydig cells. The purified rat Leydig cells were cultured in the presence of LHRH analogue (ICI 118630) (10-7 M) and after an initial lag period (2h) a marked stimulation of testosterone production occurred over a 32-h period (up to 400 ng/10(6) cells). The response to LH alone increased with time in culture up to 10 h, and the LHRH analogue enhanced this LH-stimulated testosterone production. When the cells were cultured for longer time periods (24 h) the LHRH analogue was found to inhibit LH-stimulated testosterone production at all concentrations of LH used (p less than 0.01). The LHRH analogue had no consistent effect on LH-stimulated cyclic AMP production, although when added alone, cyclic AMP production was increased. These results show that LHRH analogues do not bind to or have any detectable effect on mouse Leydig cells in vitro. However, LHRH analogue does bind specifically to purified rat Leydig cells. After a short lag period the analogue stimulates testosterone production which turns to inhibition after 20 h in culture.