Postural Augmentation of Plasma Renin Activity and Aldosterone Excretion in Normal People*

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Abstract
Peripheral plasma renin activity and aldosterone excretion rates have been measured in normal people during recumbency, recumbent exercise, tilting, and continuous ambulation. Upright posture induces a prompt elevation in peripheral plasma renin activity beginning in 15 minutes and peaking between 60 and 120 minutes. Aldosterone excretion is increased during 120 minutes of upright posture and correlates directly with the elevation in renin activity. Upright posture induces increased plasma renin activity regardless of the level of sodium intake in the preparatory diet. Concomitant measurements of endogenous creatinine clearance and the rates of excretion of sodium and potassium suggest that a fall in renal arterial perfusion resulting from upright posture induces increased release of renin and the subsequent secondary stimulation of aldosterone secretion. Our data indicate that the changes in plasma renin activity are due to changes in the amount of the enzyme rather than to changes in other elements of the reninangiotensin systm. This report discusses the physiologic importance of postural augmentation of renin production, emphasizing that for proper interpretation of values of plasma renin activity, posture as well as dietary factors must be considered and controlled.