Body sodium in normal subjects predisposed to hypertension

Exchangeable sodium is lower than normal in young male patients with essential hypertension. This may reflect a primary or secondary abnormality. To investigate this question, exchangeable body sodium was measured in 31 normotensive men with positive and 31 normotensive men with negative family history of essential hypertension on a normal sodium intake (150 mmol/day). Blood pressure (BP) tended to be higher in the former group (p less than 0.005) but age, urinary sodium excretion, plasma renin activity, and aldosterone levels or creatinine clearance were comparable. Exchangeable sodium averaged 100.8 +/- 7.1% in subjects with positive and 100.2 +/- 6% in those with negative family history. In both groups, exchangeable sodium was unrelated to arterial pressure. The response of exchangeable sodium to variations in dietary sodium intake was further investigated in 13 subjects with and 10 subjects without family history. The change from a low (17 mmol/day) to a high (270 mmol/day) sodium diet elevated exchangeable body sodium to a comparable extent, despite a greater increase in BP in subjects with positive family history. Sodium-dependent suppression of renin, angiotension II, aldosterone, and plasma catecholamines was comparable between the two groups. These findings suggest that body sodium is normal and adapts normally to variations in dietary sodium intake in normotensive subjects with familial predisposition to hypertension. Body sodium depletion in early hypertension appears to be a secondary rather than a primary event.