INORGANIC-PHOSPHATE CONTENT AND FREE-ENERGY CHANGE OF ATP HYDROLYSIS IN REGIONAL SHORT-TERM HIBERNATING MYOCARDIUM

Objective: Short-term myocardial hibernation is characterized by an ad aptation of contractile function to the reduced blood flow, the recove ry of creatine phosphate content and lactate balance back towards norm al, whereas ATP content remains reduced at a constant level. We examin ed the hypothesis that, despite: the absence of ATP recovery, the shor t-term hibernating myocardium regains an energetic balance. Methods: A n enzymatic method was modified for the measurement of inorganic phosp hate (P-i) in transmural myocardial drill biopsies (about 5 mg). In 12 anaesthetized swine, moderate ischemia was induced by reduction of co ronary inflow into the cannulated left anterior descending coronary ar tery to decrease regional myocardial function (sonomicrometry) by 50%. Results: The development of short-term hibernation was verified by th e recovery of creatine phosphate content, the persistence of inotropic reserve in response to dobutamine and the absence of necrosis (triphe nyl tetrazolium chloride). At 5-min ischemia, P-i was increased from 3 .6 +/- 0.3 (SD) to 8.1 +/- 1.1 mu mol/g(wet wt) (p < 0.05). The free e nergy of ATP hydrolysis (Delta G(ATP)) was decreased from -57.8 +/- 0. 8 to -52.21 +/- 1.4 kJ/mol (p < 0.05). The relationships between funct ion and P-i (r = -0.81) and Delta G(ATP) (r = -0.83), respectively, du ring control and at 5-min ischemia became invalid at 90-min ischemia, as myocardial blood flow and function remained reduced at a constant l evel, but P-i decreased back to 4.9 +/- 0.9 mu mol/g (p < 0.05 vs, con trol and 5-min ischemia): and Delta G(ATP) fully recovered back to -57 .2 +/- 1.3 kJ/mol (p < 0.05 vs. 5-min ischemia). Conclusions: In short -term hibernating myocardium, myocardial inorganic phosphate content r ecovers partially and the free energy change of ATP hydrolysis returns to control values. Contractile function remains reduced by mechanisms other than an energetic deficit. (C) 1998 Elsevier Science B.V. All r ights reserved.