STUDIES OF HYPOXEMIC REOXYGENATION INJURY - WITHOUT AORTIC CLAMPING .6. COUNTERACTION OF OXIDANT DAMAGE BY EXOGENOUS ANTIOXIDANTS - N-(2-MERCAPTOPROPIONYL)-GLYCINE AND CATALASE/

This study tests the hypothesis that antioxidants administered before reoxygenation can reduce oxygen-mediated damage and improve myocardial performance. Of 25 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg) five underwent 60 minutes of cardiopulmonary bypass without hypoxemia (control group), and five others underwent 30 minutes of hypoxemia on cardiopulmonary bypass with a circuit primed with oxygen tension about 25 mm Hg blood followed by reoxygenation on cardiopulmonary bypass (n o treatment). In vitro studies were performed to obtain the optimal do sage of the antioxidants N-(2-mercaptopropionyl)-glycine and and catal ase to be used in subsequent in vivo experimental studies; cardiac hom ogenates were incubated in 0 to 5 mmol/L concentrations of the oxidant t-butylhydroperoxide and malondialdehyde production was measured. Fif teen piglets were made hypoxemic on cardiopulmonary bypass for 30 minu tes, and the antioxidants N-(2-mercaptopropionyl) -glycine at either 3 0 or 80 mg/kg body weight or N-(2-mercaptopropionyl)-glycine, 30 mg/kg body weight, and catalase, 50,000 U/kg body weight, were added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation. Left ventricular contractility, which was expressed as end-systolic elastan ce, was measured by conductance catheter before hypoxemia and after re oxygenation, Myocardial antioxidant reserve capacity was determined af ter reoxygenation by incubating cardiac homogenates in the oxidant t-b utylhydroperoxide and measuring subsequent malondialdehyde elution. Th e in vitro bioassay studies showed a dose-dependent reduction of lipid peroxidation with N-(2-mercaptopropionyl) -glycine, with maximal bene fits of a 40% decrease and malondialdehyde elaboration occurring with N-(2-mercaptopropionyl)-glycine and catalase compared with untreated c ardiac homogenates. Cardiopulmonary bypass (no hypoxemia) caused no ox idant damage or changes in contractile function after cardiopulmonary bypass. Reoxygenation without treatment raised conjugated diene levels 57%, lowered antioxidant reserve capacity 51%,* and was associated w ith only 38% recovery of contractile function (p < 0.05 vs control), In contrast, treatment with antioxidants avoided lipid peroxidation, m aintained antioxidant reserve capacity, and resulted in a dose-depende nt improvement in left ventricular contractility with complete recover y occurring in N-(2-mercaptopropionyl)-glycine and catalase-treated pi glets (p < 0.05 vs no treatment). This study confirms the occurrence of hypoxemic/reoxygenation injury in immature hearts placed on cardiop ulmonary bypass and shows that biochemical and functional damage can b e counteracted by adding antioxidants to the cardiopulmonary bypass pr iming fluid. Contractile function improved in a dose-dependent manner, and oxygen-mediated damage could be avoided by mercaptopropionyl glyc ine/catalase treatment. In vitro studies were helpful to determine dru g dosages to be used in in vivo experiments and may be useful to reduc e the number of whole animal experiments required to develop optimal d osage regimens.