Age-related changes in endocrine and renal function in patients with essential hypertension

Endocrine and renal functions were studied in 149 patients with essential hypertension by measuring plasma electrolytes, renin activity, creatinine and aldoserone, as well as the urinary excretion of creatinine and sodium chloride, before and during treatment for hypertension. Half of the patients responded to trichlormethiazide (thiazide-responsive group) but the other half did not (thiazide-unresponsive group). Systolic and diastolic blood pressures increased progressively uith age in the thiazide-unresponsive group, but were lower and did not progress with age in the thiazide-responsive group. There was no consistent difference in plasma renin activity between the thiazide-responsive and the thiazide-unresponsive groups. The fluctuation of plasma renin activity in response to an excess of sodium chloride or to thiazide treatment was reduced progressively with age. Creatinine clearance decreased and the blood urea nitrogen level increased with age. The age-related decrease of plasma renin activity is discussed on the light of the age-related impairment in the ability of the kidney to excrete sodium and water.