ON THE MECHANISM OF RENIN STIMULATION

Abstract

Abstract The correlation between hemoconcentration (expressed by increase in colloid osmotic pressure (ΔCOP)) and plasma renin activity increase (ΔPRA) has been investigated during 1) change of posture from supine to standing position in normals, who were salt‐depleted the three previous days (10 mEq Na + per day, on the third day 100 mg chlortalidone (Hygrotone®)); and 2) in exercise experiments on normals on liberal salt intake in sitting position on bicycle ergometer (medium work load‐terminal pulse rate 120–140). The correlation ΔCOP‐ΔPRA was in 1) linear and significant, r =0.83, p < 0.001. The slope of the line was significantly steeper than in corresponding experiments on liberal salt intake (PRA increase per unit COP increase was greater). Mean supine PRA was significantly higher than on liberal salt intake, but the range overlapped. In 2) a significant PRA increase in all experiments appeared, but no correlation ΔCOP‐ΔPRA. It is concluded that salt depletion of some days' duration (chronic) sensibilizes the renin releasing mechanism for the postural stimulus. The lack of correlation ΔCOP‐ΔPRA for the exercise studies suggests a mechanism for renin stimulation different from the one in postural shift and acute salt depletion.