The proposed research is directed at the definition of coronary infusates which afford optimum metabolic support for the oxygen-deficient heart. It is therefore concerned with the energetic basis of cardiac performance during myocardial ischemia or hypoxia. The mechanism by which pyruvate and possibly other metabolites can improve mechanical function of oxygen-deficient hearts shall be studied. Thus, the influence of pyruvate on glycolysis, PDH flux and fatty acid 8-oxidation will be studied in relation to function and energy state as well as lactate and adenosine release of oxygen-deficient hearts. Using a hemoglobin-free perfused working rat or guinea pig heart preparation, the left ventricle will perform pressure-volume work at defined pre- and afterloads. Hemodynamic and metabolic perameters will be tested in presence of catecholamines, methylxanthines, and cardiac glycosides. High flow oxygen deficiency (hypoxia) will be compared with low flow oxygen deficiency (ischemia). The effects of metabolically inert mannitol will also be tested. Cardiac performance will be measured using strain gages, flow meters, heart rate meters, and a multichannel recorder. Hypoxia will be obtained by reducing the oxygen concentration in the inflow perfusate. Ischemia will be induced by reducing coronary perfusion pressure such that flow autoregulation cannot compensate for the fall in aortic pressure. Oxidative metabolism will be judged by oxygen uptake (platinum O2-electrode) and 14CO2 production from specifically labeled substrates ((1-14C)-pyruvate, (3,4-14C) glucose, (1-14C) fatty acid). Anaerobic metabolism will be evaluated from adenosine plus inosine release, lactate/pyruvate ratios and glycolytic flux, the latter estimated from release of tritiated water in presence of (3-3H)D-glucose. Myocardial energy state, i.e. the ratio (ATP)/(ADP)x(Pi), will be calculated from the creatine kinase equilibrium or (in normoxic hearts) from the concentrations of pyruvate, lactate, glycerinaldehyde phosphate and 3-phosphaglycerate using published reaction constants. Metabolites will be measured in tissue extracts and/or perfusion fluids applying standardized as well as recently established enzymatic analytical procedures. Metabolic rates will be calculated from coronary arterio-venous concentration differences of metabolites and coronary flow.
