CHANGES OF MYOCARDIAL HIGH-ENERGY PHOSPHATES WITH THE CARDIAC CYCLE DURING ACUTE OR CHRONIC MYOCARDIAL STRESS

Whether changes of cardiac high-energy phosphate concentrations occur over the cardiac cycle remains controversial, The hypothesis was that such cyclical changes are accentuated during acute or chronic myocardi al stress, Isolated rat hearts were perfused under four conditions: (1 ) control, (2) inotropic stimulation by doubling of perfusate [Ca2+], (3) acute hypoxia (buffer PO2 similar to 150 torr), and (4) failing, c hronically infarcted hearts, P-31-MR spectra were obtained at seven ti me points of the cardiac cycle, Under control conditions, cyclical cha nges (''cycling'') of ATP (11 +/- 3%, *P < 0.05) and phosphocreatine (9 +/- 2%) were detected, inorganic phosphate cycling did not reach s tatistical significance, At high [Ca2+] perfusion, cycling of phosphoc reatine (9 +/- 5%) was not accentuated, cycling of ATP and inorganic phosphate did not reach significance, During acute hypoxia, cycling of ATP (10 +/- 4%) and inorganic phosphate (11 +/- 4%*) occurred, but c yclical changes of phosphocreatine were not significant. In chronicall y infarcted hearts, the extent of cyclical changes of ATP, phosphocrea tine, and inorganic phosphate was not accentuated, Thus, in perfused r at heart, small oscillations of high-energy phosphates during the card iac cycle are detectable, but such changes are not accentuated during acute or chronic stress. The concentrations of high-energy phosphates over the cardiac cycle are tightly regulated.