EFFECTS OF PROPRANOLOL AND DILTIAZEM ON THE RATE OF HIGH-ENERGY PHOSPHATE-METABOLISM IN REPERFUSED RAT HEARTS - P-31-NMR SATURATION-TRANSFER STUDY

The relationships between pressure rate product (PRP) and flux (PCr--> ATP) or flux (Pi-->ATP) were studied in isolated perfused rat hearts b y the saturation transfer method using P-31-NMR. The effects of propra nolol and diltiazem on phosphate metabolism were also studied. After a 40 min preischemic period, the hearts were subjected to a 15 min peri od of ischemia, followed by 60 min of reperfusion. Propranolol (0.4-1. 2 muM) or diltiazem (3.0-6.0 muM) was infused for 30 min before ischem ia and reinfused after reperfusion for 60 min. The flux (PCr-->ATP)/PR P ratio at reperfusion did not differ from that at preischemia. This v alue was also not affected by propranolol or diltiazem treatment. Howe ver, the flux (Pi-->ATP)/PRP ratio at reperfusion was significantly le ss than that at preischemia. Moreover, this value was significantly im proved by propranolol or diltiazem treatment. This study demonstrates that 1) flux (PCr-->ATP) has a good correlation with cardiac performan ce, 2) stunned myocardium needs less ATP turnover for survival of its depressed contractile activity, and 3) flux (Pi-->ATP) can limit recov ery of postischemic performance. Protective effects of propranolol and diltiazem are exerted on the flux (Pi-->ATP), i.e. ATP derived from g lycolytic flux, in the reperfused heart.