14 November 2008
A number of cardiac metabolic intermediates, namely, adenosine triphosphate (ATP), H+, phosphocreatine (PCr), inorganic phosphate (Pi), adenosine diphosphate (ADP), and related functions of these intermediates, Gibbs’ free energy of ATP hydrolysis (ΔG) and phosphorylation ratio [ATP/(ADP·Pi)], are thought to adjust mitochondrial oxidative phosphorylation rates to conform to mechanical demand. The effects of hypothermia and altered perfusion pressure on these parameters were evaluated in 12 hearts from Sprague-Dawley rats perfused in the Langendorff mode. <sup>31</sup>P-nuclear magnetic resonance (NMR) spectra were obtained at cardiac temperatures between 20 and 37 °C, and coronary perfusion pressures between 20 and 145 cm H<sub>2</sub>O. Coronary flow varied between 0.5 and 15ml/min throughout this range of intervention. Heart rate (HR), left ventricular systolic pressure (LVSP), and specific volumetric coronary flow (SCF) were determined for each temperature and perfusion pressure. The product HR × LVSP directly correlated with perfusion pressure at all temperatures. The temperature dependence could be represented by an overall activation energy of 72.7 kJ/M. In the constant temperature experiment, SCF and HR × LVSP fell linearly with decreasing perfusion pressure. Quantitative evaluation of the relationship between cardiac function and the metabolic intermediates described above defined these intermediates as nonregulatory with the possible exception of H+.