[Role of a purified Sertoli cell protein (CMB-21) in the biosynthesis of Leydig cell testosterone in the immature rat].

The existence of Sertoli cell factors which modulate the rat Leydig cell function prompted us to study the biological activity of selected proteins called CMB proteins and produced by immature rat Sertoli cells. Percoll purified Leydig cells (10(5)) from 20 days-old rats have been incubated 5 h at 32 degrees C in 1 ml Ham F12/DME medium with increasing concentrations of partially purified CMB proteins (0-1,000 ng/ml) either in presence or absence of oLH (25 ng/ml). Among the CMB proteins tested, only CMB-21 produces a dose related increase of testosterone production: from 2 to 500 pg/ml of CMB-21, testosterone output is unchanged (51 pg/10(5) cells) but 1 to 1,000 ng/ml of this protein produces a linear increase of testosterone productions (86 to 870 pg). In the presence of oLH which induces a 10-fold increase of testosterone production (499 pg), increasing doses of CMB-21 further stimulate testosterone output (775 to 2.272 pg/10(5) cells). Whatever the concentration of oLH used (0 to 50 ng/ml), CMB-21 (500 ng/ml) leads to a further 2 fold augmentation of testosterone synthesis; similarly, in the presence of dbcAMP (1 mM), CMB 21 increases the testosterone production but no effect is observed when Leydig cells are incubated in the presence of 22R-hydroxycholesterol (30 microM). The cAMP levels which are increased more than 4 fold by oLH, remain unchanged in the presence of CMB-21 either alone or with oLH, as observed when Sertoli cell culture medium is used.(ABSTRACT TRUNCATED AT 250 WORDS)