Effect of Short-Term Upright Posture on Plasma Angiotensin II in Man

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Abstract
The effect of upright posture on radioimmunologically measured venous plasma angiotensin II was studied in healthy volunteers, using active (continuous walking) and passive (head-up tilting) types of upright posture. Blood samples were drawn 1, 3, 10, 30 and 90 minutes after assumption of an upright posture. Significantly increased concentrations of angiotensin II were found 10 minutes after the change of posture. In the active test the initial rise was more marked, whereas at 90 minutes significantly more angiotensin II was found in the passive test. The initial rise in the active test was slightly slower in subjects over 60 years of age. During the conditions used the diurnal variation of angiotensin II was not found to affect markedly the response of angiotensin II to upright posture. The present data suggest that angiotensin II does not play any significant role in the maintenance of blood pressure right after the change of posture from supine to upright. Later, angiotensin II is obviously linked to the maintenance of adequate circulating blood volume, but its significance in the maintenance of blood pressure remains obscure.