Plasma release of atrial natriuretic peptide in response to blood volume expansion

The response of plasma atrial natriuretic peptide (ANP) concentration to acute intravascular volume expansion was measured in ten male Wistar rats. An infusion of 3 ml polygelene colloidal solution at 37 degrees C over 45 s produced peak venous pressure rises of 1.5 cm water. A highly significant (P less than 0.001) rise of immunoreactive plasma ANP from 24.4 +/- 2.2 (mean +/- S.E.M.) pmol/l to a peak of 70.0 +/- 10.5 pmol/l occurred within 2.5 min. Plasma ANP concentrations had virtually returned to basal levels (32.7 +/- 2.7 pmol/l) 30 min after this acute volume load. A further infusion of 10 ml polygelene colloidal solution in 2 min produced peak venous pressure rises of 10 cm water and caused a dramatic and significant (P less than 0.001) increase of plasma ANP concentration to a peak of 534.8 +/- 38.5 pmol/l, occurring 7.5 min after infusion. The plasma ANP concentration had fallen but remained above basal levels 30 min later (137.2 +/- 26.4 pmol/l). Similar results were obtained using an identical protocol but with whole rat blood instead of polygelene solution as the volume-expanding agent. Gel column chromatography suggested that the majority of the immunoreactive ANP in rat plasma was of similar molecular size to rat alpha-ANP (1-28). These results support the hypothesis that blood volume expansion is a potent stimulus for the release of ANP into plasma.