Effects of age on renal sodium homeostasis and its relevance to sodium sensitivity.

Age-related changes in blood pressure, renal function, and sodium homeostasis suggest that sodium sensitivity of blood pressure may also be influenced by age. Blood pressure was measured in 378 normal volunteers and 198 patients with essential hypertension after an intravenous infusion of normal saline and after sodium and volume depletion. Those whose mean arterial blood pressure decreased more than 10 mm Hg after sodium and volume depletion were considered sodium-sensitive, whereas those with a decrease of less than 5 mm Hg were considered sodium resistant. The normal and hypertensive subjects were divided into groups of those above and those below 40 years of age. The blood pressure responses of both older and younger groups were normally distributed, indicating that blood pressure could either decrease or increase following volume depletion. Older hypertensive and normotensive subjects are more likely to be sodium sensitive. They usually have lower renin values than do younger subjects, but substantial heterogeneity is found. Age and renin status do not reliably predict sodium sensitivity. Volume contraction and dietary sodium restriction are more likely to decrease blood pressure in older than in younger subjects, but regimens must be tailored individually.