The Effects of Dietary Sodium on the Diurnal Activity of the Renin-Angiotensin-Aldosterone System and the Excretion of Urinary Electrolytes

Diurnal variations of five normal men were tested over three 24 h consecutive periodsThe first experiment began at 0900 h after the subjects had fasted for 12 h and a normal sodium diet of about 70–80 mEq was given at 0900 h, 1200 h, and 1630 h (total of about 220 mEq of Na)Significant variations in the plasma renin activity (PRA), in the plasma aldosterone (PA), and inthe urinary Na and k outputs were found. The second experiment began at 1200 h with the first feeding time at 2100 h after fasting about24 h and the subjects were given a normal sodium diet as inthe first experiment, but with the meals given at 2100 h, 2400 h, and 0430 h. The diurnal variations in PRA, plasma aldosterone, and urinary electrolytes disappeared. From this study, it appears that the diurnal variation in urinary electrolyte excretion is a factor of the diurnal variation inPRA and plasma aldosterone. The diurnal variation in PRA and plasma aldosterone are related to thetiming of sodium ingestion.