Reactivity to alpha agonists is heightened in immature porcine pulmonary arteries

Background. Pulmonary hypertension after cardiopulmonary bypass is a common problem in pediatric cardiac operations. This study tested the hypothesis that there is a difference between adult and immature pulmonary artery constrictor and dilator responses. Methods. Reactivity of pulmonary artery ring segments from 22 mature (15 to 19 weeks) and 15 immature pigs (4 to 5 weeks) was tested in a vessel myograph. Potassium as s receptor-independent vasoconstrictor and phenylephrine as an α-receptor-mediated vasoconstrictor were used to assess smooth-muscle vasoconstriction. To assess endothelial cell function (nitric oxide production and secretion), we used increasing concentrations of bradykinin or acetylcholine. Sodium nitroprusside was used to produce maximum smooth-muscle relaxation at the end of each experiment. Results. The data demonstrated maturation-independent endothelium and smooth-muscle-mediated vasodilation. Pulmonary artery ring segments from immature pigs had significantly less KCI constriction compared with mature pigs (p < 0.05). In contrast, pulmonary ring segments from immature pigs demonstrated enhanced α-receptor-mediated constriction compared with mature pigs. Conclusions. These data may explain perioperative pulmonary vasoconstriction in pediatric patients.