Objective: A diurnal variation in urine output has been described in humans, whereby it is lowest at night. Fluid balance hormones such as vasopressin and aldosterone as well as urine output have a diurnal variation. Although the diurnal variation of vasopressin results in part from a circadian rhythm, the variation in aldosterone has until recently been reported to be due to the sleep/wake cycle. The present study used a specialized protocol to explore whether aldosterone has an underlying circadian rhythm.
Methods: Ten healthy participants (average age 23.1) were enrolled in the 57.3-hour protocol that included an 8-hour baseline sleep episode, 40 hours in constant routine conditions (wakefulness, food and fluid intake, posture, and dim light), and a 9.3-hour recovery sleep. Blood samples for aldosterone were taken every 4 hours. Cosinor analysis was performed on the constant routine data to test the effect of the sleep/wake cycle on overall aldosterone secretion.
Results: There was a significant circadian rhythm during the 40-hour constant routine, independent of sleep, with aldosterone higher at the end of the biological night and lower at the end of the biological day. When analyzing data from the entire 57.3-hour protocol and controlling for this circadian rhythm, aldosterone concentration was significantly higher during the recovery night following the 40-hour sleep deprivation compared to the night spent awake.
Conclusion: We found a significant endogenous circadian rhythm in the secretion of aldosterone, independent of sleep. In addition, as shown previously, there was a significant effect of the sleep/wake cycle on aldosterone secretion.
Keywords: Circadian; Constant routine; Nocturia; Urine output.
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