Study on the renin-angiotensin-aldosterone system. Effects of sodium restriction and postural changes on plasma renin activity and fluctuation in urinary aldosterone

Abstract

Recent observations have demonstrated that the renin-angiotensin system is concerned with the regulation of aldosterone secretion and blood pressure, and measurement of plasma renin activity (PRA) can contribute to a great extent to the evaluation of patients with hypertension. It has been already certified that PRA is significantly and extremely suppressed in patients with primary aldosteronism. The following experiments were studied about the most effective diagnostics of primary aldosteronism, the optimum and convenient conditions for measuring PRA in sodium restriction and upright position and furthermore the incidence of primary aldosteronism among patients with essential hypertension, and evaluation of the renin-angiotensin-aldosterone system in patients with various kinds of hypertension. Materials and Methods. 76 patients with essential hypertension 4 with renovascular hypertension, 10 with primary aldosteronism and 9 normal subjects were examined in these studies. Each subject was fed on a diet containing various amounts of sodium (300mEq, 130mEq, 30-40mEq) for at least three days prior to study. A sample of peripheral venous blood was obtained in the morning after overnight recumbency and after two to four hours of upright position plus thiazide administratoin (Fig. 1). PRA was measured by BOUCHER'S method and urinary aldosterone was determined by blue tetrazolium coloration (or double isotope derivative method) utilizing our new systems of thin layer chromatography instead of paper chromatography because of the economy of time and cost without the sacrifice of accuracy (Fig.2, 3). R Results: Recumbent PRA was a little more increased in a group taking 130 mEq/day sodium than 300 mEq/day sodium and more effectively increased in a severe restriction of sodium intake (30-40 mEq) and most definitely increased on a low sodium diet combined with upright ambulation. Each subject should be fed on a low sodium diet for at least four days to examine PRA (Table I and II). The study on an optimum time for measuring PRA increase in upright ambulation showed a maximum increase after 180-240 min as compared with values obtained after 60 minutes, but usually showed the almost sufficient values after 120 minutes (Fig. 5).