Lipid droplets in the secretory response of Leydig cells of normal and hCG-treated rats.

Prolonged (7-day) hCG infusion caused a remarkable hypertrophy of rat Leydig cells, coupled with a notable enhancement of their basal and stimulated testosterone production in vitro. It also provoked a conspicuous accumulation of lipid droplets in the cytoplasm of hypertrophic cells. The administration of 4-aminopyrazolo-pyrimidine (4APP), at a dose causing a significant hypocholesterolaemia, did not affect the morphology and function of Leydig cells in normal rats. Conversely, in chronically hCG-infused animals, 4APP reversed lipid-droplet accumulation and significantly depressed stimulated testosterone production. The following conclusions are drawn: 1) chronic hCG treatment enhances the ability of rat Leydig cells to take-up exogenous cholesterol from circulating lipoproteins, and to store it in lipid droplets as a reserve material; 2) lipid-droplet stored cholesterol is employed only in the case of intense acute stimulation, since, under basal conditions, endogenous cholesterol synthesis is able to meet the requirements for testosterone production alone.