Insulin Level, RBC Na+ Transport and Blood Pressure in Cushing's Syndrome

Abstract

To test the hypothesis that hyperinsulinemia and / or abnormalities of RBC Na+ transport are concerned in the pathogenesis of hypertension in Cushing's syndrome, we 'investigated the relationship between insulin level, RBC Na + transport and blood pressure in patients with Cushing's syndrome which is frequently associated with hyperinsulinemia, abnormalities of RBC Na + transport and hypertension. Both systolic and diastolic pressure were significantly higher in Cushing's syndrome than in normal subjects. Fasting serum insulin level was higher and both serum glucose and insulin responses after a 75g glucose load were significantly increased in patients with Cushing's syndrome as compared with normal subjects. Both RBC Na+ concentration and passive Na + permeability were significantly lower but Vmax of Na +, K+-pump was significantly higher in patients with Cushing's syndrome than in normal subjects, while Vmaxs of Na+-K+ cotransport and Na+-Li + countertransport were similar in the two groups. In multiple stepwise regression analysis for patients with Cushing's syndrome, fasting serum insulin level was directly correlated with both systolic and diastolic pressures (r=O. 52, p=O. 01; r=O. 51, p=O. 02, respectively). On the other hand,RBC Na + transport parameters showed little correlation with either systolic or diastolic pressures. These results suggest that hyperinsulinemia may contribute to the hypertension in Cushing's syndrome, but that the abnormalities of RBC Na + transport seen in Cushing's syndrome are not causally related to hypertension.