An Analysis of Factors Determining the Circadian Pattern of Aldosterone Excretion

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Abstract
There is an apparent circadian rhythm in the secretion of aldosterone by normal active subjects which is reflected in the excretion of larger quantities of aldosterone in the forenoon than at other times of the day. The aldosterone rhythm is not abolished by the administration of dexamethasone in doses sufficient to suppress 17-hydroxycorticosteroids to negligible values. The aldosterone rhythm can be suppressed, however, by having the subjects remain recumbent at all times. When normal subjects assume the upright posture at 8 pm rather than at 8 am, their aldosterone values are higher at night than during the day. The increase in aldosterone excretion which occurs after assumption of upright posture at 8 am is followed by a decrease in aldosterone values in the afternoon, despite continued maintenance of upright posture. Under all these circumstances changes in plasma renin activity tend to parallel those in aldosterone excretion. It is concluded that posture is the dominant factor conferring apparent circadian rhythmicity on aldosterone secretion and that the effect of posture is mediated by changes in renin secretion.