Vasodilatation of intrapulmonary arteries to P2-receptor nucleotides in normal and pulmonary hypertensive newborn piglets.

1. The vasodilator responses of isolated intrapulmonary arteries (IPA) to P2-receptor agonists were investigated during adaptation to extrauterine life in the piglet. The effect of pulmonary hypertension on the normal response was determined after exposing newborn animals to chronic hypobaric hypoxia (51 kPa) for 3 days. 2. Adenosine 5'-triphosphate (ATP), 2-methylthioATP (2-meSATP), adenosine 5-O-(2-thiodiphos-phate) (ADPbetaS) and uridine 5'-triphosphate (UTP) induced a relaxation in normal newborn piglet IPA pre-contracted with prostaglandin F2alpha (PGF2alpha). The relaxations were not affected by removal of the endothelium. The responses to ATP and ADPbetaS increased significantly with age. 3. The relaxation responses of IPA to ATP, 2-meSATP and ADPbetaS continued to increase normally after birth in an hypoxic environment. 4. The results of the study show that vasodilatation of porcine intrapulmonary vessels to nucleotides increased during development from foetus to adult; that the vasodilatation to purines was mediated by P2Y-receptors on the vascular smooth muscle rather than on the endothelium; and that the P2Y-receptor mediated relaxation of IPA remained normal in the pulmonary hypertensive neonate.