Bilirubin as an antioxidant: Effect on group B streptococci-induced pulmonary hypertension in infant piglets

Bilirubin scavenges toxic oxygen radicals in vitro, but it is not known whether this potential salutary effect can be extended to the intact animal. Accordingly, the present experiments tested the hypothesis that bilirubin protects against oxygen radical-dependent pulmonary hypertension and arterial hypoxemia in piglets infected with group B streptococci (GBS). Piglets ranging in age and weight from 7 to 14 days and 1.5 to 2.0kg, respectively were infused for 60 min with 108 cfu GBS/kg/min. One group of 7 animals was pretreated with a bolus infusion of 15mg/kg of bilirubin followed by a continuous bilirubin infusion. A second group of 7 animals was given the vehicle. While plasma bilirubin levels in control animals were negligible, administration of exogenous bilirubin was associated with plasma levels of 13.0 ± 0.74mg%. Piglets treated with exogenous bilirubin exhibited GBS-induced increases in pulmonary arterial pressure and decreases in PaO₂ of 16.1 ± 2.0 and 46.5 ± 4.3 torr, respectively. In control animals, GBS increased pulmonary arterial pressure and decreased PaO₂ by 17.5 ± 1.6 and 47.9 ± 3.2 torr, respectively. Neither the peak changes in pulmonary arterial pressure or PaO₂ nor the time courses of these alterations differed between treatment groups. These observations indicate that bilirubin fails to prevent GBS-induced pulmonary hypertension and arterial hypoxemia in infant piglets and suggests that in this particular model bilirubin does not exhibit appreciable oxygen radical scavenging activity.