Renal tubular handling of sodium and familial predisposition to essential hypertension.

Renal clearance of lithium and sodium, glomerular filtration rate, renal plasma flow and certain other parameters of proximal tubular function were determined in 10 normotensive men without, and 13 normotensive men with a family history of essential hypertension after a low- and high-sodium diet. Under low-sodium conditions, the two groups did not differ in mean body weight, exchangeable sodium, plasma renin activity, clearances of inulin, para-aminohippurate (PAH), lithium, sodium, potassium, uric acid or inorganic phosphate, although blood pressure tended to be slightly, but not significantly, higher in those with a family history of hypertension. After changing to the high sodium diet, body weight, exchangeable sodium, and sodium clearance increased and renin decreased significantly (P less than 0.05) and to a similar extent in the two groups; systolic blood pressure increased only in subjects with a family history of hypertension. In both groups renal clearances of inulin, PAH, lithium, potassium, uric acid and inorganic phosphate remained unchanged. These findings do not support the concept that familial predisposition to hypertension is associated with an enhanced proximal reabsorption of sodium. Moreover, the pressor response to a high sodium intake in predisposed subjects is not mediated by an abnormal adaptation of renal sodium metabolism.