Insulin binding sites in solubilized membranes from rat testis. Effect of age.

The effect of aging on the binding of insulin to testicular solubilized microsomal membranes was studied in rats. The insulin receptor was solubilized in triton x-100 and its properties compared with those of solubilized membranes of rat liver. At the three life stages studied (21, 38-40 and 75-80 days) binding specificity in testicular solubilized membranes showed the following order of competition relative to porcine insulin (100): proinsulin (7), guinea-pig insulin and IGF-I (less than 1).

Characterization of insulin binding and comparative action of insulin and insulin-like growth factor I on purified Leydig cells from the adult rat.

Insulin binding and insulin action were characterized in adult rat Leydig cells, purified on discontinuous Percoll gradients. Binding of [125I]-porcine insulin was found to be dependent on time, temperature, cell concentration and Leydig cell specific gravity. Competition relative to porcine insulin (100) was as follows: insulin-like growth factor I (IGF-I) : less than 1; proinsulin : 5; guinea-pig insulin : 2; hCG, ovine prolactin and bovine GH : 0.