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
