Biological activity of endogenous atrial natriuretic peptide during cardiopulmonary bypass

To evaluate the effect of cardiopulmonary bypass (CPB) on atrial natriuretic peptide (ANP) biological activity in patients undergoing cardiac operations, we conducted a prospective study. Ten patients undergoing mitral valve surgery were enrolled. Plasma levels of ANP and cyclic guanosine monophosphate (cGMP), hemodynamic variables, and renal function parameters were assessed perioperatively. The molar ratio of cGMP to ANP (as a marker for ANP biological activity) decreased significantly (p < 0.05) during CPB despite similar plasma ANP levels. The ratio correlated inversely with the duration of CPB (r = -0.85, p = 0.002). The ratio also correlated with fractional sodium excretion (r = 0.65, p = 0.04) and correlated inversely with pulmonary vascular resistance (r = -0.79, p = 0.009) and atrial filling pressure (r = -0.84, p= 0.003) postoperatively. CPB decreased the molar ratio of cGMP to ANP, which may represent ANP biological activity, such as vasodilation and natriuresis. The phenomenon may contribute to water-sodium retention and pulmonary hypertension after cardiac surgery.