Effects of norepinephrine infusion on myocardial high-energy phosphate content and turnover in the living rat

Abstract

Using 31P-nuclear magnetic resonance, we studied the relationship between myocardial high-energy phosphate content and flux values for the creatine kinase reaction in the living rat under inotropic states achieved during norepinephrine infusion and halothane anesthesia. Under 2% halothane anesthesia (n = 4), 1% halothane anesthesia (n = 5) and norepinephrine infusion (n = 4), rats developed rate-pressure products of 19.5±1.6, 32.0±3.5, and 48.5±2.0 x 1,000 mmHg/min, respectively. Adenosine triphosphate content was not affected by inotropic state, ranging from 24.3±1.1 to 25.6±1.1 μmol/g dry weight, but creatine phosphate content varied inversely and reversibly with cardiac performance from 45.6±6.0 under 2% halothane to 26.0±6.5 μmol/g dry weight during norepinephrine infusion. The flux values for the creatine kinase reaction were 15.4±4.6, 20.5±2.0, and 30.1±7.9 μmol/g dry weight per s under 2% halothane, 1% halothane, and 1% halothane with norepinephrine, respectively. These results suggest that the turnover of myocardial high-energy phosphate compounds, not their tissue contents, matches cardiac performance during inotropic stimulation.