Splenic macrophages can modify steroidogenesis of Leydig cells

A large amount of LH/hCG treatment given to male rats is known to suppress the enzyme activity of cytochrome P450(c17) in Leydig cells for 48 h. A high dose LH/hCG injection is also known to allow immunocytes, such as macrophages, to migrate into the testicular interstitial compartment. It has not been known, however, whether these cells play a role in that suppression. In this study, we examined if splenic macrophages have any effects on testosterone secretion from Leydig cells by culturing rat testicular interstitial cells (TIC). Splenic macrophages co-cultured with TIC significantly suppressed testosterone secretion. Macrophages co-cultured reduced both progesterone to testosterone conversion and the amount of cytochrome P450(c17) mRNA. The conditioned medium (SMCM), prepared by culturing macrophages for 12 h, significantly reduced either testosterone secretion from TIC or progesterone to testosterone conversion by TIG. These results indicate that splenic macrophages suppress testosterone secretion from Leydig cells by suppressing the cytochrome P450(c17) enzyme in vitro, and that this effect is mediated at least in part by some soluble factors secreted from macrophages. Splenic macrophages migrating into the testis after LH/hCG stimulation could play a role in suppressing cytochrome P450(c17) in Leydig cells.