Biological activity of endogenous atrial natriuretic peptide during cardiopulmonary bypass

To evaluate the effect of cardiopulmonary bypass (CPB) on atrial natriureti c peptide (ANP) biological activity in patients undergoing cardiac operatio ns, we conducted a prospective study. Ten patients undergoing mitral valve surgery were enrolled. Plasma levels of ANP and cyclic guanosine monophosph ate (cGMP), hemodynamic variables, and renal function parameters were asses sed perioperatively. The molar ratio of cGMP to ANP las a marker for ANP bi ological activity) decreased significantly (p < 0.05) during CPB despite si milar plasma ANP levels. The ratio correlated inversely with the duration o f CPB (r = -0.85, p = 0.002). The ratio also correlated with fractional sod ium 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 t o ANP, which may represent ANP biological activity, such as vasodilation an d natriuresis. The phenomenon may contribute to water-sodium retention and pulmonary hypertension after cardiac surgery.