EFFECTS OF POSTURE ON THE PLASMA HORMONAL AND RENAL WATER-ELECTROLYTEEXCRETORY RESPONSES TO ACUTE WATER LOADING IN DIABETIC SUBJECTS WITH HYPOADRENERGIC ORTHOSTATIC HYPOTENSION

The effects of posture on the plasma hormonal and renal water-electrol yte excretory responses to acute water loading (20 mL/kg BW, orally) w ere studied in six non-insulin-dependent diabetes mellitus (NIDDM) sub jects with hypoadrenergic orthostatic hypotension (HOH), eight NIDDM s ubjects without HOW, and seven nondiabetic subjects. The three groups were similar with respect to basal levels of mean blood pressure (MBP) , serum sodium and osmolality, plasma renin activity (PRA), the plasma volume regulatory hormones alpha-atrial natriuretic peptide (ANP), ar ginine vasopressin (AVP) and aldosterone, and urinary water and sodium excretion. In the supine state, while allowing the subjects to stand only to void, water loading resulted in no changes in MBP and similar responses of these plasma and urinary parameters in the three groups. In the standing state, water loading produced responses of MBP, and pl asma and urinary parameters comparable to those in the supine state in the diabetic group without HOH and the nondiabetic group. In the diab etic group with HOH, however, MBP and hourly urinary water and sodium excretion rates were low compared to those in the other two groups. Du ring water loading plasma ANP decreased, and, despite the fall of MBP, plasma AVP remained unchanged, and PRA and plasma aldosterone increas ed normally in the diabetic group with HOH. These results demonstrate that, in NIDDM subjects with HOH, changing from lying to standing indu ces deranged renal water and sodium handling after water loading, acco mpanied by a decrease in plasma ANP, and inadequate responses of plasm a AVP, PRA, and plasma aldosterone to hypotension.