Effect of Cardiopulmonary Bypass on Biological Activity of Atrial Natriuretic Peptide

Purpose of study, Hypothermia, exclusion of pulmonary circulation and atrial manipulation during cardiopulmonary bypass (CPB) may influence biological activity of endogenous atrial natriuretic peptide (ANP). To evaluate the effect of CPB on ANP biological activity in patients undergoing cardiac operations, we conducted a prospective study. Methods used. Ten patients undergoing mitral valve surgery were enrolled in this study. Plasma levels of ANP and cyclic guanosine monophosphate (cGMP), hemodynamic variables and renal function parameters were assessed perioperatively. Biological activity of ANP was determined by the molar ratio ofcGMP to ANP. Results. Preoperative biological activity of ANP correlated inversely with pulmonary vascular resistance (r=−0.62, p=0.04). Although plasma ANP levels did not change perioperatively, plasma cGMP levels decreased significantly (at the start of CPB, 7.0 ± 1.7; at the end of CPB, 1.7 ± 0.6, p=0.01) during CPB. Biological activity of ANP, determined by the molar ratio of cGMP to ANP, decreased significantly during CPB (at the start of CPB, 434±166; at the end of CPB, 92±13, p=0.01). Biological activity of ANP at the end of CPB correlated inversely with the duration of CPB (r=−0.85, p=0.002) and correlated with the fractional sodium excretion during the first 6 hours after initiation of CPB (r=0.65, p=0.04). Conclusions. The results suggest that biological activity of endogenous ANP decreases during CPB, despite similar plasma ANP levels. The decrease may be associated with water-sodium retention after CPB.