NITRIC-OXIDE SYNTHASE (NOS-I) IN LEYDIG-CELLS OF THE HUMAN TESTIS

By means of immunocytochemical methods, immunoreactivity for the brain isoform of nitric oxide synthase (NOS-I) was recognized in numerous L eydig cells of the human testis as well as in MA-10 tumor and TM3 non- tumor mouse Leydig cell lines, Within the Leydig cell cytoplasm, immun ocytochemical results suggested the occurrence of factors known to act ivate NOS-I such as glutamate and aspartate, as well as molecules invo lved in the regulation of the NOS-I activity such as calmodulin and C2 +/calmodulin-dependent protein kinase II. Leydig cells, Sertoli cells, some endothelial cells of the testis, MA-10- and TM3 mouse Leydig cel l lines exhibited a relatively strong NADPH-diaphorase enzyme activity as well. Double sequential immunostainings provided evidence that NOS -like immunoreactivity of the testicular Leydig cells is colocalized w ith testosterone, calmodulin, aspartate, glutamate, and Ca2+/calmoduli n-dependent protein kinase II, Sodium nitroprusside treatment did not result in increased cGMP formation by MA-10- or TM3 mouse Leydig cells , suggesting that NO produced by these cells acts primarily in a parac rine fashion, The NO produced by NOS-I immunoreactive Leydig cells may act as a messenger: 1) between neighbouring NOS-I positive and/or neg ative Leydig cells as well as to mediate the action of numerous intrac ellular and extracellular neuroactive substances and growth factors; 2 ) between Leydig cells and the muscle cells or pericytes of blood vess els to regulate local blood flow and permeability; and 3) between Leyd ig cells and peritubular myofibroblasts to influence their contraction and the permeability of the lamina propria.