Lack of diurnal rhythm in plasma atrial natriuretic peptide.

The occurrence of a circadian rhythm in the concentration of circulating atrial natriuretic peptide (ANP) is not clearly established. To investigate diurnal changes, plasma levels of ANP were measured at 10-min intervals for 24 hours in six normal volunteers. The subjects were studied once during a normal sleep-wake cycle and once during a cycle with a shifted sleep period. They received continuous enteral nutrition from 8 hours preceding the experiment until the end of the experiment, throughout this time the subjects remained in a supine position. The mean ANP levels did not differ significantly between the sleep periods and the periods spent awake in either of the protocols, which provides evidence of a lack of a sleep-related influence of ANP. A significant linearity of the mean ANP profile was observed, smoothing out the transient and randomly occurring fluctuations in individual ANP concentration. These results lead to the conclusion that ANP secretion is neither under the control of endogenous circadian rhythmicity nor is it affected by sleep-regulatory mechanisms.