POSITRON-EMISSION-TOMOGRAPHY ANALYSIS OF [1-C-11]ACETATE KINETICS IN SHORT-TERM HIBERNATING MYOCARDIUM

Background-Modeling of the time-[1-C-11]acetate activity curve assumes constant concentration of labeled tricarboxylic acid cycle intermedia tes and associated metabolites, such as glutamate and aspartate, which may, however, decrease in short-term hibernating myocardium. Methods and Results-In 12 anesthetized pigs, [1-C-11]acetate was injected as a bolus into the cannulated left anterior descending coronary artery du ring normoperfusion, inotropic stimulation, ard early (5 to 45 minutes ) and prolonged ischemia (60 to 90 minutes). Regional myocardial oxyge n consumption (M(V) over dot O-2, microliters per minute per gram) was measured, and the absence of necrosis was verified by triphenyl tetra zolium chloride staining. Inotropic stimulation increased M(V) over do t O-2 from 52.5 +/- 7.4 to 195.4 +/- 36.2 (mean+/-SD) and the rate con stant (k(mono), minutes(-1)) of [1-C-11]acetates clearance from 0.094 +/- 0.018 to 0.322 +/- 0.076. During early ischemia, M(V) over dot O-2 and k(mono) were decreased to 24.3 +/- 8.5 and 0.061 +/- 0.011, respe ctively. K-mono closely correlated to M(V) over dot O-2 during normope rfusion, inotropic stimulation, and early ischemia. In short-term hibe rnating myocardium, however, at an unchanged M(V) over dot O-2, k(mono ) increased toward control values (0.080 +/- 0.014). Myocardial glutam ate and aspartate concentrations (biopsies) decreased to 47 +/- 26% an d 77 +/- 18%; the peak count rate decreased to 66 +/- 22% of its respe ctive control value. After correction for the decreases in glutamate a nd aspartate or in peak count rate, k(mono) was again decreased (0.050 +/- 0.016 or 0.052 +/- 0.014, respectively), and a close relationship to M(V) over dot O-2 was restored. Conclusions-K-mono correlates to M (V) over dot O-2 in short-term hibernating myocardium when the decreas es in aspartate and glutamate or in peak count rate are considered.