PHENYLISOPROPYL ADENOSINE (PIA) PREVENTS INCREASE IN PULMONARY ARTERY PRESSURE DURING HYPOXIA IN NEWBORN LAMBS

Abstract

Adenosine analogs are potent vasodilators. In newborn lambs we tested the hypothesis that PIA would decrease the pulmonary artery pressure (PAP) without significant decrease in aortic pressure (AoP). Catheters were placed in the pulmonary artery, aorta and inferior vena cava. After 48 hr. the following variables were measured: PAP, AoP, heart rate (HR), respiratory rate (RR), and arterial blood gases. Five sets of experiments were performed in 3 animals: 1) hypoxia (9% FiO2), 2) PIA, 3) PIA+hypoxia. A dose-response curve for PIA (5 to 60 mcg/kg IV bolus) was established. Mean PAP increased with hypoxia (from 12±3 to 27±2 torr p<0.001, PaO2 18±3 torr). After PIA pre-treatment, hypoxia (PaO2 24±3 torr) did not change the mean PAP (13±4 to 13±6 NS). The AoP did not change with hypoxia, nor with PIA + hypoxia (85±4 to 88±12 and 87±11 to 74±20 torr, NS). HR increased with hypoxia (from 165±21 to 320±39 p <0.004) and decreased with PIA (191±18 to 145±21/min., p<0.007). RR increased with hypoxia (38±7 to 56±8/min. p<0.03). PaO2 decreased during hypoxia and PIA+hypoxia (79±11 to 18±3, p<0.008, and 79±4 to 24±3 torr, p<0.001). PCO2 and pH did not change. These results suggest that PIA prevents increase in PAP during severe hypoxia without decreasing the AoP.