Superior cavopulmonary anastomosis suppresses the activity and expression of pulmonary angiotensin-converting enzyme

Abstract

Background: Superior cavopulmonary anastomosis is widely used for palliation of various forms of univentricular heart defects. However, clinically significant pulmonary arteriovenous malformations develop in 15% to 25% of patients after surgery. Objective: To assess altered regulation of pulmonary vascular tone caused by superior cavopulmonary anastomosis in an ovine model. Methods: Lambs, aged 35 to 45 days, underwent an end-to-end anastomosis of the superior vena cava to the right pulmonary artery. In age-matched controls, a sham operation was performed. Arteriovenous malformations were detectable by contrast echocardiography by 8 weeks after surgery. Animals (n = 24) were studied at various time points after the operations. Expression of angiotensin-converting enzyme messenger RNA, protein levels, and enzyme activity were measured in lung homogenates. Levels of angiotensin II were measured by enzyme-linked immunosorbent assay. Results: Expression of angiotensin-converting enzyme messenger RNA and protein was significantly reduced at 1 to 5 weeks after superior cavopulmonary anastomosis. Angiotensin-converting enzyme activity in the right lung of animals subjected to superior cavopulmonary anastomosis was reduced 86% ± 1% (standard deviation) compared with control values at 1 week ( P = .003) and 77% ± 8.5% at 2 weeks ( P < .001) after surgery. This correlated with a 59% ± 3.5% ( P = .007) reduction in angiotensin II levels up to 5 weeks after cavopulmonary anastomosis. By 15 weeks after the operations, angiotensin II levels were equivalent to control levels ( P = .19). Conclusions: Superior cavopulmonary anastomosis causes an early reversible reduction in activity and expression of angiotensin-converting enzyme, resulting in decreased circulating levels of the vasoconstrictor angiotensin II. These results suggest that the ability of the pulmonary endothelium to regulate vascular tone is inhibited after superior cavopulmonary anastomosis. Dilation of the affected vasculature induced by cavopulmonary anastomosis may contribute to the disordered vascular remodeling observed in this setting.