Ultrastructure of leydig cells in the African green monkey

Active Leydig cells of Cercopithecus aetiops occur singly or in clusters in the intertubular areas. They are characterized by a polymorphic smooth endoplasmic reticulum (SER), constituted of tubules, whorls of cisternae, and concentric rings surrounding lipid droplets. Some aspects of the endoplasmic reticulum, described in other mammals during nonbreeding periods, demonstrate that the variable forms of SER are not necessarily linked to cell activity. Mitochondria are variable in form and associated with the elements of SER usually observed in steroid-producing cells. The presence of thin filaments between lipid droplets and mitochondria may represent the morphologic aspect of their hypothesized function of cholesterol transport to mitochondria. Golgi system-derived vesicles appear much more numerous and easy to recognize in replicas than in sections. This observation may confirm a secretory process, as suggested by previous observations.