Effect of exercise in the heat on plasma renin and aldosterone with either water or a potassium-rich electrolyte solution.

Information concerning the renin-angiotension-aldosterone system during physical exercise in the heat with adequate fluid and/or electrolyte supplement is lacking. The present study was intended to describe the changes in renin activity and serum aldosterone, serum sodium, and serum potassium in subjects receiving water or a potassium-rich electrolyte solution while exercising (50% VO2 max) for 120 min in a warm environment (32 degrees C, 50% relative humidity). This study shows that, in subjects receiving the electrolyte supplement, serum potassium is elevated slightly during the exercise period whereas serum sodium is unchanged from preexercise levels without the electrolyte supplement. Plasma renin and aldosterone levels were significantly reduced in the subjects receiving the electrolyte supplement compared to subjects receiving only water. The ingestion of the electrolyte supplement replaced 42% of the sodium and 100% of the potassium lost by way of sweat and urine while exercising in the heat.