Variation of Plasma Renin Concentration During a 24-Hour Period

The present investigation was undertaken to determine the extent to which plasma renin concentration varies during a 24-hr. period of unrestricted activity. Seven healthy male medical students (aged 20–24) were investigated. Five samples (50 ml.) were taken from an arm vein at 6-hourly intervals from each student at the times indicated in Fig. 1. Since repeated sampling might have produced systematic changes in renin concentration (see Brown, Davies, Lever, Robertson & Verniory, 1965), the experiment was started at different times in individual subjects. In two, the first sample was taken at 10.00 a.m.; in three, at 4.00 p.m.; and in the remaining two at 10.00 p.m. Samples were taken with the subjects in the recumbent position. No attempt was made to limit physical activity or dietary intake during the period of the study. All subjects had been sleeping in the hours before the 4.00 a.m. sample. Plasma renin concentration was