PRECONDITIONING WITH HYPOXIA VERSUS GLOBAL-ISCHEMIA IN THE ISOLATED RAT-HEART - EFFECT ON FUNCTION AND METABOLISM

It has recently been shown that hypoxia and ischemia are equally effec tive to precondition the myocardium of the rat. A comparison of the me tabolic changes caused by transient ischemia and hypoxia has not yet b een made and may help to elucidate the metabolic factors involved in e liciting preconditioning. The aim of this study was to compare the cha nges in tissue high energy phosphates, glycogen and lactate during and after hypoxic and ischemic preconditioning in isolated perfused rat h earts. Isolated rat hearts were subjected to global ischemia of 30 min utes duration, with and without preconditioning consisting of a single episode of 5 minutes global ischemia or hypoxia (PO2 = 12kPa). The po st-ischemic recovery of aortic flow of the nonpreconditioned group was significantly less than that of the two preconditioned groups: 0. 5 /- 0.5 ml/min vs. 23.3 +/- 3.4 and 20. 7 +/- 3.6 ml/min for ischemic a nd hypoxic preconditioning respectively. The only common metabolic fac tor between the two preconditioned groups was the similar extent of gl ycogenolysis after transient ischemia or hypoxia: glycogen decreased f rom 22 +/- 0.8 in non-preconditioned hearts to 16 +/- 0. 5 and 16 +/- 1.5 mumoles glucose per g wet tissue in ischemic and hypoxic precondit ioned hearts respectively. There was also no difference in lactate pro duction between the two groups during the sustained episode of ischemi a. We conclude that oxygen deprivation, rather than other metabolic fa ctors, is the important factor in eliciting preconditioning.