Circadian Rhythms of Plasma Renin Levels in the Anesthetized Rat

Circadian rhythms of plasma renin activity (PRA) is described in the ether anesthetized rat. PRA values are significantly higher than corresponding values previously reported in the awake rat. Peak activity was observed at 12.00 and 16.00 h, similar to the pattern of diurnal rhythm established in the conscious rat. The reproducibility of PRA in the anesthetized rat is demonstrated by relatively constant values obtained from a separate group of rats bled at the same hour every other week. In addition, each sample was also incubated with excess renin substrate for the determination of relative plasma renin concentration (PRC). The pattern obtained for PRC is similar to that of PRA, indicating that the circadian rhythms result from variations of plasma renin rather than changes in renin substrate. Furthermore, although ether anesthesia raises the basal levels of PRA, it does not interfere with the demonstration of the normal pattern of circadian rhythms.