Hyporeninemia: A novel form of orthostatic intolerance

Orthostatic intolerance occurs in many patients but its pathophysiology is poorly understood. We tested the hypothesis that defects in sympathetic innervation of the kidney might cause reduced plasma renin activity (PRA) which could, in turn, underlie the hypovolemia encountered in many such patients. Sixteen patients (14F, 2M) ranging in age from 16 to 44 years were studied. Patients were enrolled in the study if they had orthostatic tachycardia or syncope together with raised circulating plasma norepinephrine levels 0 600 pg/ml). Patients underwent a battery of tests including hemodynamic variables, blood volume (TBV), PRA, and plasma catecholamines. There was a strong positive correlation between the change in blood volume and PUA (r=0. 8, 0. 80, and p=0-000, 0. 0006 for supine and upright PRA, respectively). PRA also correlated with plasma aldosterone levels. These data indicate that in patients with orthostatic intolerance, there is a close correlation between the blood volume and PRA. This may indicate an important role for the inappropriately low PRA in mediating hypovolemia.