The actions of insulin-like growth factors I and II on cultured Sertoli cells.

Cultured Sertoli cells prepared from young rats (13 days old) showed increased incorporation of [3H]thymidine into DNA, increased production of lactate, and increased incorporation of [3H]leucine into protein in response to micromolar concentrations of insulin and nanomolar concentrations of insulin-like growth factor II (IGF-II). The first of these responses was also seen with nanomolar concentrations of IGF-I. Receptor affinity labeling studies using Sertoli cell membranes and whole Sertoli cells showed that these cells possess abundant growth factor receptors of type I (mol wt, 350,000) that show high affinity for IGF-I, moderate affinity for IGF-II, and low affinity for insulin. Sertoli cell membranes also show abundant growth factor receptors of type II (mol wt, 230,000) that show high affinity for IGF-II, moderate affinity for IGF-I, and no detectable affinity for insulin. Moreover, the responses of the Sertoli cell to insulin were observed at concentrations of 100 nM or higher, whereas insulin receptors are known to be saturated by insulin at concentrations of 10 nM or less. It is, therefore, concluded that Sertoli cells possess receptors for IGF-I and that the responses observed to insulin may result from binding of these hormones to receptors for IGF-I.