Rate of pyridine nucleotide oxidation and cytochrome oxidase interaction with intracellular oxygen in hearts from rats with compensated volume overload.

Abstract

Volume overload was created in rats by means of an aortocaval fistula. The animals were sacrificed after the fistula had been in place for 1 month, at which time most of the animals were in the compensated stage of cardiac hypertrophy. Their hearts were excised and used for in vitro perfusions. Their ability to oxidize an excess of reduced pyridine nucleotide (state 5 to state 3 transition) was tested fluorometrically during recovery from a short period of anoxic perfusion. In a parallel series of experiments, the kinetics of myoglobin reoxygenation and cytochromeaa3 reoxidation were studied by means of double wave length recordings of myoglobin (581–621 nm) and cytochromeaa3 (606–626 nm) absorption changes. The sequential analysis of a series of reflectance spectra was also used to assess the range of mean intracellular oxygen concentrations (myoglobin O2-saturation) compatible with unlimited respiration (full oxidation of cytochromeaa3). Normoxic and anoxic patterns of adenine nucleotide phosphorylation, as well as the patterns of coenzyme A esterification were determined biochemically in order to assess the state of respiratory control at the level of the initial span of the respiratory chain. The results are as follows: (1) hearts from animals with compensated volume overload reoxidized an anoxia induced excess of NADH more rapidly than those of controls. (2) The improved oxidation of reduced pyridine nucleotide was not related to changes in coronary perfusion, since coronary flow rate (ml/min gdw) as well as the rate of myoglobin reoxydation were unchanged. Total tissue phosphocreatine contents and total tissue ATP/ADP·Pi ratio were comparable in control and overloaded hearts, both under normoxic conditions, and after 2 min of anoxia. (3) On the other hand, anoxic patterns of coenzyme A esterification differed significantly: while in control hearts, there was an accumulation of long chain acyl-CoA during anoxia, no such change was observed in overloaded hearts. (4) During recovery from anoxia, the preanoxic reduction degree of cytochromeaa3 appeared at lower level of intracellular meanpO2 in overloaded hearts, as compared with controls. This was suggested by the degree of myoglobin O2-saturation that was simultaneously detected.