Salt-sensitivity testing in patients with borderline hypertension: reproducibility and potential mechanisms

We examined the reproducibility of dietary salt-sensitivity testing by studying the effects on blood pressure (BP) of low sodium intake (20 mmol/day) and high sodium intake (220 mmol/day) in 10 men with borderline hypertension on two separate occasions. A difference in mean arterial pressure of 8 mm Hg between the high salt and the low salt regimen was arbitrarily chosen to define salt sensitivity. In addition, the reproducibility of changes in renal haemodynamics and in humoral factors, such as plasma renin activity, plasma aldosterone, atrial natriuretic peptide and urinary dopa and dopamine excretion, on the alteration in sodium intake were studied. As far as changes in BP are concerned, there was perfect agreement between the two tests, because in the second investigation, all subjects were classified in the same category as before. The salt-induced changes in plasma atrial natriuretic peptide and in renal excretion of dopa (dihydroxyphenylalanine) and dopamine were repeatedly and consistently different between the salt-sensitive and the salt-resistant group. The study revealed no support for a role of renal haemodynamics or the renin-angiotensin-aldosterone system in the pathophysiology of salt-induced elevations of BP in salt-sensitive subjects.