24-HOUR PROFILES OF PLASMA-RENIN ACTIVITY IN RELATION TO THE SLEEP-WAKE CYCLE

Objective: To evaluate the relative contribution of sleep and the endo genous circadian rhythmicity in producing the 24-h variations in the p lasma renin activity. Methods: Ten normal young men were studied, unde r basal conditions with normal nocturnal sleep from 2300-0700 h and on ce after a night of total sleep deprivation followed by 8 h daytime sl eep from 0700 to 1500 h. Plasma renin activity was measured every 10 m in for 24 h and the profiles were analysed using the pulse detection p rogram ULTRA. Results: During the 8 h night-time sleep a significant i ncrease in the mean plasma renin activity levels occurred compared wit h the subsequent 8-h waking periods. After the shift in the sleep peri od, a sleep-associated increase was clearly apparent during the daytim e hours. The number and the amplitude of the oscillations, linked to t he non-rapid eye movement-rapid eye movement sleep cycles, increased d uring sleep (at whatever time it occurred), and were dependent on the regularity and the length of the sleep cycles. In awake subjects the p lasma renin activity generally fluctuated in a more damped and irregul ar manner, but occasionally the plasma renin activity oscillated at a regular periodicity with two dominant peaks centred around 100 and 50 min. Conclusion: These results demonstrate that the 24-h plasma renin activity variations are not circadian in nature but are related to sle ep processes, which create the nycthemeral rhythm by increasing both t he frequency and the amplitude oi the oscillations.