Increased insulin binding of erythrocytes and insulin sensitivity in adrenal insufficiency

We have studied 125I-insulin binding to erythrocytes (RBC) in five patients with hypoadrenocortisolism, and compared to 17 normal subjects and in nine patients with Cushing's syndrome. In another study insulin sensitivity index (ISI) was measured by the IV insulin tolerance test in four patients with hypoadrenocortisolism (1.82 +/- 0.15 mg/dL/min), and compared to 19 normal subjects and 23 patients with Cushing's syndrome (1.56 +/- 0.1 mg/min/dL). Mean insulin binding in hypocortisolism was 17.9 +/- 0.7%, and was significantly higher (P less than .01) than in normal subjects (12.0 +/- 1.4%) and was significantly (P less than .001) decreased toward normal (11.8 +/- 1.47) during replacement therapy. Increased binding in untreated hypoadrenocortisolism was due to elevated high affinity site receptor concentration as compared to the treated patients (0.10 +/- 0.015 v 0.053 +/- 0.003 nmol/L,P less than .01). These results suggest that increased insulin binding in chronic hypoadrenocortisolism may be attributed to increased insulin binding to the receptor, which can revert to normal by replacement therapy. The role of increased insulin binding to increased insulin sensitivity in hypoadrenocortisolism is discussed.