1. Adrenomedullin (AM), a potent hypotensive peptide, was originally isolated from human phaeochromocytoma. Plasma AM concentrations are elevated in hypertension, heart failure and renal failure in proportion to the severity of the disease. This study was performed to investigate the pathophysiological significance of AM during cardiac surgery.

2. Serial blood samples were obtained from patients undergoing cardiac surgery and plasma AM concentrations were determined by specific radioimmunoassay.

3. Plasma AM concentrations did not increase with anaesthesia or surgery (n = 9). Plasma AM concentrations gradually increased during cardiopulmonary bypass and after pulmonary reperfusion. After pulmonary reperfusion, plasma AM concentrations increased further. In addition, we measured plasma AM concentrations in the pulmonary vein (n = 8) and coronary sinus (n = 8) to examine the contribution of the lungs and heart to the increase in circulating AM concentrations after cardiopulmonary bypass. However, no significant differences were seen in plasma AM concentrations of the pulmonary vein or the coronary sinus and the aorta. Peak AM concentrations during cardiac surgery correlated with duration of surgery. Elevated plasma AM levels during and after surgery began to decline next day after surgery and returned to normal levels 7 days after surgery.

4. These results demonstrate that plasma AM concentrations increase during cardiac surgery and that the duration of surgery may be related to the changes in AM concentrations. Taken together with recent findings that vascular endothelial cells and vascular smooth muscle cells actively produce AM, these results suggest that plasma AM during cardiac surgery may act as a vasodilatory hormone.

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