Effects of dietary sodium restriction and posture on plasma levels of atrial natriuretic peptide, aldosterone and free aldosterone in normal human pregnancy.

The effects of dietary sodium restriction and posture on plasma concentrations of atrial natriuretic peptide (ANP), aldosterone and free aldosterone were investigated in ten women between weeks 29 and 33 of normal pregnancy. Hormone levels were studied during unrestricted sodium intake and on day 6 of a low sodium diet. On both occasions venous blood was obtained in the sitting as well as in the left lateral tilt position. Plasma concentrations of ANP during the unrestricted sodium intake were not raised compared with control values in healthy non-pregnant females. Recovery experiments showed no differences in the degradation of ANP in blood from pregnant and non-pregnant women. Plasma concentrations of ANP significantly decreased (by 32%) in response to the low sodium regime in both positions. Concentrations of aldosterone and free aldosterone (in women in the sitting position) increased twofold after sodium restriction. Mean values of ANP were higher in women in the left lateral tilt position that in those in the sitting position, but the difference was not significant. Concentrations of aldosterone and free aldosterone were significantly lower (by around 30%) in women in the left lateral tilt position compared with those in the sitting posture.