Regulation of atrial natriuretic peptide release in pregnancy: responses to posture.

Abstract

The response of plasma atrial natriuretic peptide to three changes in posture that alter atrial stretch was examined in the late phase of pregnancy: (1) after 20 minutes in lateral recumbency, remaining upright for 2 hours decreased median plasma atrial natriuretic peptide values from 37.8 (25th percentile, 22.9 and 75th percentile; 64.2) to 21.8 (10.1 and 28.4) pg/ml in pregnant women (p less than 0.05) and from 39.2 (27.8 and 51.2) to 24.0 (18.9 and 35.4) pg/ml (p less than 0.001) in age-matched nonpregnant women; (2) prolongation of lateral recumbency from 20 to 80 minutes increased median plasma atrial natriuretic peptide levels from 31.9 (25.6 and 37.3) to 47.8 (33.0 and 74.6) pg/ml in pregnant women (p less than 0.001) and from 36.5 (22 and 58.6) to 54.0 (36.3 and 111.7) pg/ml in nonpregnant women (p less than 0.01); (3) adoption of supine posture during the late phase of normal pregnancy did not alter median plasma atrial natriuretic peptide values significantly [30.4 (26.7 and 42.5) pg/ml during lateral recumbency compared with 34.2 (25.4 and 43.5) pg/ml while supine]. Plasma atrial natriuretic peptide values fell after supine posture in only half the women and supine hypotension occurred in one subject. These studies demonstrate that upright and prolonged lateral recumbent postures significantly influence plasma atrial natriuretic peptide values during pregnancy, as they do in the nonpregnant state, but that supine posture does not alter plasma atrial natriuretic peptide values significantly. Posture must be carefully accounted for in any study of plasma atrial natriuretic peptide in pregnancy.