Mechanism of hyperoxia-induced pulmonary vascular paralysis: effect of antioxidant pretreatment.

We designed experiments using isolated rabbit lungs to determine the effect of hyperoxia on the pulmonary vasoconstriction caused by the infusion of the lipid peroxide tert-butyl hydroperoxide (t-bu-OOH), which produces vasoconstriction by stimulating the pulmonary synthesis of thromboxane. Exposure to 48-60 h of 100% O2 at 1 ATA markedly reduced the increase in pulmonary artery pressure caused by t-bu-OOH infusion. We also investigated whether the mechanism for the attenuated vasoconstriction was due to altered production of arachidonate mediators or oxidant-induced damage to the contractile mechanism. In addition to infusing t-bu-OOH, which selectively stimulates thromboxane production, we also infused Intralipid, an esterified fatty acid emulsion that stimulates production of both thromboxane and prostacyclin. These experiments were done to study the effect of hyperoxia on prostacyclin synthesis. To determine if antioxidant therapy would prevent the changes in mediator production and vascular reactivity caused by hyperoxia, we pretreated animals with the antioxidants butylated hydroxyanisole (BHA) or vitamin E. The lack of vascular reactivity to t-bu-OOH was not due to a decrease in thromboxane synthesis or an increase in prostacyclin synthesis. Hyperoxia did not affect thromboxane synthesis during basal conditions or after stimulation of synthesis by t-bu-OOH. 100% O2 also did not effect the basal synthesis of prostacyclin by the lung. Hyperoxia did, however, markedly reduce prostacyclin synthesis when it was stimulated by Intralipid infusion. Antioxidant pretreatment did not reverse the inhibition of prostacyclin synthesis but did prevent the loss of vascular reactivity caused by hyperoxia. Thus hyperoxia causes vascular paralysis through oxidant-induced injury to the pulmonary vasculature.