Abstract
For the quantitative analysis of the effect of sodium balance on renin secretion, plasma renin activity (PRA) was measured in 9 healthy young males in the respective 3- or 4-day periods of sodium repletion, mild sodium restriction, moderate and severe sodium depletion. In the latter 2 periods, sodium balance was made negative by low salt diet and furosemide administration (120mg/day, p.o.) for 1 or 3 days. Blood samples for PRA determination were obtained at supine position (8:00 a.m.) and after 1-, 2-, and 4-hour's upright posture. PRA was also measured after furosemide stimulation (80mg, p.o.) plus 2-hour's upright posture in the period of sodium repletion.
Change in the supine PRA was directly correlated with that in hematocrit (r=0.81) and inversely with that in body weight (r=-0.64). The PRA rose significantly from 1- to 2- and 4-hour's upright posture in the period of mild sodium restriction, whereas it reached the maximum level at 1-hour's upright posture and remained unchanged thereafter in either period of negative sodium balance. The upright PRA after furosemide stimulation in the period of sodium repletion was almost identical to 2- and 4-hour's upright PRA in the period of mild sodiom restriction, and less than 1-hour's upright PRA in either period of negative sodium balance.
These data suggest that 1-hour's upright posture is enough to evaluate PRA when sodium balance is negative.
