Stage-specific inhibition of interstitial cell testosterone secretion by rat seminiferous tubules in vitro

The stage-specific influence of the secretions from rat seminiferous tubules on the LH-stimulated testosterone production by rat Leydig cells in vitro was studied. The spent media from incubated seminiferous tubules (SMST) from stages VII-VIII of the seminiferous epithelial cycle caused about 50% inhibition of the LH-dependent testosterone production by a crude preparation of rat interstitial cells. The SMST from other stages had no effect on testosterone production. Mixed tubules of unidentified stages gave an intermediate response. When SMST from ten different stages of the seminiferous wave were compared, the most pronounced inhibitory activity was found in stages VI and VIII–XI, while SMST from stages I, VII and XIII–XIV had no inhibitory effects on interstitial cell testosterone production. No stimulation was found in this system. Prolonged incubation of the interstitial cells with SMST from stages VIII–XI resulted in loss of inhibitory activity after 12 h of incubation. Maximum inhibitory activity was noted after 3 h of incubation. The inhibitory activity of the SMST from stages VIII–XI was retained after prolonged dialysis, and was unchanged after heating the medium at 60°C for 1 h. The activity did not seem to be due to the presence of proteolytic enzymes, since it was not influenced by addition of protease inhibitors. SMST from stages VIII–XI had no effect on the metabolism of [ 3H]testosterone added to the interstitial cell preparations. No inhibitory effect was observed when Leydig cells were incubated with dibutyryl cAMP instead of LH, suggesting an early influence on the LH-receptor-adenylate cyclase chain of events. A gradual increase in the inhibitory action of SMST from stages VIII–XI was noted with increasing age of the animals. When Percoll-purified Leydig cells were used, no inhibitory activity was observed with any of the media tested. In contrast, stimulation of Leydig cell testosterone production resulted with all kinds of SMST tested. The different results with crude interstitial cells and purified Leydig cells may indicate either that other cells (macrophages?) are involved in the inhibitory activity on the crude cells, or that purified cells represent only a subpopulation of the Leydig cells.