Ultrastructural localization of the NADPH-diaphorase activity in the Leydig cells of aging mice

Recently, it has been shown that nitric oxide may inhibit the Leydig cell s teroidogenesis. The present paper describes, by means of NADPH-diaphorase h istochemistry, the ultrastructural localization of the enzyme nitric oxide synthase in the Leydig cells of young adult and aging mice. In the young ad ult mice, the enzymatic reaction was mainly located in the mitochondria and in some clustered cisterna: of the smooth endoplasmic reticulum. The nucle ar envelope was faintly labeled. In the aging mice, most Leydig cells showe d an enhanced enzymatic reaction. Labeled mitochondria were increased in nu mber, and labeled areas of the smooth endoplasmic reticulum were more numer ous and extended. In addition, a strong enzymatic reaction was recognized i n the nuclear envelope. We conjecture that the impaired steroidogenesis obs erved in the testis of aging mammals might, at least in part, depend on the increased nitric oxide production in the Leydig cells.