Insulin Binding Sites and Action in the Adrenal Glands from Normal and Streptozotocin Diabetic Rats

Insulin binding to rat adrenal glands was studied in vivo by i.v. injection of 125I-insulin either alone or together with an excess of unlabelled hormones (insulin, glucagon, prolactin, or growth hormone). In addition, isolated glands from normal or streptozotocin diabetic rats (STZ) were incubated in vitro with 125I-insulin and varying concentrations of unlabelled insulin. Both experiments showed specific binding sites in the adrenal glands. Furthermore the glands from diabetic rats bound more insulin than the glands from controls. The insulin stimulatory effect on the deoxyglucose (14C-DG) uptake was examined in isolated glands from normal and STZ rats. Adrenal glands from control rats exhibited higher basal values of 14C-DG uptake than glands from STZ rats. Insulin induced a stimulatory effect on the 14C-DG transport in glands from both control and diabetic rats. Adrenal glands from STZ rats responded much earlier to exogenous insulin, however the maximal stimulating concentration of the hormone did not restore the 14C-DG uptake to control values. The lowest concentration of insulin that increased the 14C-DG transport was 3 X 10(-8) M. The adrenal gland must be considered a target organ for insulin by both criteria, insulin specific binding and stimulatory action on the deoxyglucose transport.