Modulation of steroidogenic activities in testis Leydig cells.

Recent developments in the regulation of testicular Leydig-cell function support the following conclusions. (1) Enzymic activities involved in steroid production in the testis are mainly localized in Leydig cells. The aromatase enzyme complex for oestrogen production appears to be localized in Leydig cells as well as in Sertoli cells. (2) LH- (or hCG-) induced alterations of Leydig cells depend on dose and duration of exposure of the cell to the hormone. Locally produced oestradiol is probably involved in the inhibition of steroidogenesis. (3) The stimulatory action of LH on Leydig cells involves different proteins in concert with the activation of the cleavage activity of mitochondrial cholesterol side-chain. However, most of the functional properties of these proteins are yet unknown. (4) Different populations of Leydig cells are present in the testis. These different cell populations can be characterized by quantitatively and qualitatively different responses to hormones.