Stimulatory effect of Sertoli cell secretory products on testosterone secretion by purified Leydig cells in primary culture.

We investigated the influence of media from nonstimulated (SCCM) and FSH-stimulated (F-SCCM) cultured rat Sertoli cells on testosterone secretion by purified rat Leydig cells maintained in culture for 4 days. Both SCCM and F-SCCM stimulated Leydig cell secretory activity to a level 2-6 times that of the control, the effect being always maximal on day 3 of culture. On day 3, concentrated SCCM had a greater stimulatory effect on testosterone secretion than the original (i.e. non-concentrated) one, the effect being dose-related and similar to that exerted by concentrated F-SCCM. On the other hand, original as well as concentrated F-SCCM stimulated the basal testosterone secretion in a dose-dependent manner on day 1 to about 200% and 400% of the control level, respectively, whereas SCCM exerted the 'early' effect only as a concentrated preparation. Preincubation of Leydig cells with F-SCCM enhanced both basal (190% control) and LH-stimulated (274% control) testosterone secretion when the LH (10 ng/ml) was added for 3 h on day 1. The enhanced influence of SCCM was noted only with the LH-stimulated cells (140% control). It is concluded that, in culture, Sertoli cells release at least 2 factors which enhance testosterone secretion by Leydig cells in vitro. One of them seems to be FSH-dependent and increases both basal and LH-stimulated testosterone secretion. This factor (MW greater than 1 kDa) is heat-labile and exerts its maximal effect between 12 and 18 h of culture. The second factor(s) acts predominantly on day 3 of culture, is apparently FSH-independent, and its influence on Leydig cell testosterone may be, at least in part, nonspecific.