Radioautographic localization and regulation of the insulin receptors in rat testis.

Luteinizing hormone (LH) is involved in maintenance of the insulin receptor in rat Leydig cells. In the cryptorchid model, spontaneous LH elevation increases insulin binding in Leydig cell membrane; this result is confirmed by the number of insulin receptors determined by radioautography. Administration of testosterone or LH-RH to control or cryptorchid rats lower insulin binding in testis membranes indicating the key role of LH. Isolated Leydig cells respond in vitro to LH by increasing their insulin binding. Localization and specificity of this binding has been studied by radioautography and we have demonstrated the preferential localization of insulin receptor in Leydig cells vs tubular cells. We conclude that insulin plays a synergistic role with LH on steroidogenesis via a specific membrane receptor which number appears modulated by pituitary LH.