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ATP Precursor Depletion and Postischemic Myocardial Recovery' JOURNAL OF SURGICAL RESEARCH 50,629-633 (19%) ATP Precursor Depletion and Postischemic Myocardial Recovery’ STEVENF. BOLLING, M.D.,2 EDWARDL. BOVE, M.D., AND KIM P. GALLAGHER,PH.D. Thoracic Surgery Research Laboratory, Departments of Surgery (Section of Thoracic Surgery) and Physiology, Uniuersity of Michigan Medical School, Ann Arbor, Michigan 48109 Presented at the Annual Meeting of the Association for Academic Surgery, Houston, Texas, November 14-17, 1990 lized routinely. Despite these protective techniques, how- Although cardioplegia reduces myocardial metabo- ever, adenosine triphosphate (ATP) depletion may oc- lism during ischemia, adenosine triphosphate (ATP) cur during ischemia. The slow recovery of the depleted depletion occurs, which may contribute to poor func- nucleotides, especially ATP, following ischemia is well tional recovery after reperfusion. Augmenting myo- recognized. Since intracellular ATP is essential for myo- cardial adenosine during ischemia is successful in im- cardial contraction and relaxation, ATP depletion may proving ATP repletion and myocardial recovery follow- be an important factor contributing to the incomplete ing ischemia. If adenosine is an important determinant recovery of ventricular function following ischemia and of ischemic tolerance, then depletion or elimination of reperfusion. The decrease in ATP during ischemia is not myocardial adenosine should lead to poor functional accompanied by a rise in ADP, as ADP is quickly trans- and metabolic recovery after ischemia. To test this hy- formed to AMP. The dephosphorylation of AMP by pothesis, isolated, perfused rabbit hearts were sub- 5’-nucleotidase results in formulation of adenosine jected to 120 min of 34°C ischemia. Hearts received St. which is deaminated to inosine by adenosine deaminase. Thomas cardioplegia alone or cardioplegia containing Since the nucleosides can exit the myocyte, they are 200 FM adenosine, or cardioplegia containing 15, 5, 2.5, or 0.025 pg/ml adenosine deaminase (ADA), which washed out of the interstitial space during reflow and are catalyzes the breakdown of adenosine to inosine, mak- unavailable for the nucleotide salvage pathway. ing adenosine unavailable as an ATP precursor. Func- Previous studies [l-5] have demonstrated that adeno- tional recovery was determined and myocardial nu- sine-supplemented cardioplegia was associated with ac- cleotide levels were measured before, during, and after celerated repletion of ATP and improved functional re- ischemia. Following ischemia and reperfusion, control covery after reperfusion. Two-deoxycoformycin, an hearts recovered to 51 * 3% of preischemic developed agent that inhibits adenosine deaminase, was also pressure (DP). There was significantly better recovery shown to be beneficial [3], supporting the view that in adenosine-augmented hearts (68 * 7%), while ADA adenosine availability during and after global ischemia hearts had significantly worse recovery. Hearts may be an important determinant of postischemic meta- treated with 0.025 pg/ml ADA recovered to only 29 bolic and functional recovery. If this hypothesis is -+ 5% of DP and higher dose ADA hearts failed to dem- correct, then depletion or elimination of myocardial onstrate any recovery of systolic function. Further- adenosine should lead to poor functional and metabolic more, adenosine enhanced metabolic recovery, recovery after ischemia. whereas ADA resulted in greatly depleted ATP and Cardioplegia containing adenosine deaminase was ad- precursor reserves. Postischemic developed pressure ministered to isolated, perfused rabbit hearts subjected closely paralleled the availability of myocardial adeno- to global ischemia. Adenosine deaminase was used to sine, consistent with the hypothesis that myocardial accelerate the breakdown of adenosine, limiting its avail- adenosine levels at end ischemia and early reperfusion ability as an ATP precursor. The effects of adenosine are important determinants of functional recovery depletion on functional and metabolic recovery were after global ischemia. 0 1991 Academic Press, Inc. compared with the results obtained when adenosine lev- els were augmented and with a control group of isolated INTRODUCTION hearts treated with cardioplegia alone. To provide myocardial protection during cardiac sur- gery, cardioplegia and myocardial hypothermia are uti- MATERIAL AND METHODS Studies were performed in isolated, perfused rabbit ’ Supported in part by NIH Grant R01 HL32043; and by the Ameri- hearts. Male New Zealand White rabbits (3 to 4 kg) were can Heart Association of Michigan. ’ To whom reprint requests should be addressed at the University of anesthetized and cardiectomy was performed. The beat- Michigan Hospital, Section of Thoracic Surgery, 2120D Taubman ing heart was suspended from a perfusion column by Center, Box 0344, Ann Arbor, MI 48109. aortic cannulation and coronary perfusion was estab- 629 0022-4804/91 $1.50 Copyright 0 1991 by Academic Press, Inc. All rights of reproductionin any form reserved. 630 JOURNAL OF SURGICAL RESEARCH: VOL. 50, NO. 6, JUNE 1991 lished at 80 mm Hg. The perfusate used was a modified, received modified St. Thomas cardioplegia with the ad- oxygenated Krebs-Ringer bicarbonate solution (pH 7.44 dition of 200 PM adenosine (n = 4) or adenosine deami- to 7.48, 37”C, 300 to 310 mOsm/liter), with an oxygen nase 15, 5, 2.5, or 0.025 /*g/ml of cardioplegia (n = 4 tension of 550 and 650 torr. The perfusion solution was each). Specimens were taken from the left ventricle with filtered and was not recirculated. a biopsy gun during the control period, prior to reflow (at While the heart was perfused on the column, a portion end ischemia), and 1 and 15 min during reperfusion. The of the mitral valve with its chordae was excised and a biopsy specimens were frozen in liquid nitrogen immedi- latex balloon, connected to saline-filled tubing, was in- ately after they were obtained. troduced into the left ventricle (LV) through the mitral The specimens were assayed by the high performance orifice. The balloon was sewn in place in such a way to liquid chromatography (HPLC) method for myocardial allow for passive venting of the LV cavity. The balloon cellular ATP, ADP, AMP, adenosine, and phosphocre- was connected through a catheter to a pressure trans- atine levels and values are expressed as micromoles of ducer, and LV pressure was recorded continuously. Out- nucleotide per milligram of protein. Statistical analysis put from the pressure transducer was electronically dif- was performed with analysis of variance and Student’s ferentiated to enable continuous recording of dP/dt. two-tailed t test, where appropriate. A P value of less During the preischemic control period, a volume of than 0.05 was considered significant. All results are ex- saline was introduced into the LV balloon to produce an pressed as means f SEM. All animals received humane end-diastolic pressure (EDP) of 10 mm Hg. The same care in compliance with the Principles of Laboratory An- volume was used to evaluate ventricular systolic perfor- imal Care formulated by the National Society for Medi- mance during reperfusion. Coronary flow was measured cal Research. volumetrically. A thermistor needle was inserted into the midmyocardium to record myocardial temperature. After a 30-min stabilization period, control measure- RESULTS ments of end-diastolic pressure (EDP), developed pres- sure (DP, peak systolic pressure minus end-diastolic Left Ventricular Function pressure), peak positive dP/dt, and coronary flow were made in each heart. Hearts were then rendered globally There were no significant differences in the prearrest ischemic. The intraventricular balloon was deflated and DP, dP/dt, or heart rates between control hearts and 60 ml of cardioplegia was administered. All hearts were those receiving adenosine or adenosine deaminase for maintained at 34°C by means of a circulating water any group. Left ventricular systolic functional measure- jacket during 120 min of total ischemia. All hearts re- ments of DP and + dP/dt were made after 15,30, and 45 ceived 15 ml of cardioplegia every 30 min during isch- min of reperfusion. Left ventricular EDP was also mea- emia. Control hearts (n = 9) received modified St. sured in 15-min intervals following reperfusion and was Thomas cardioplegia alone, while experimental hearts expressed as an increase in EDP over the preischemic received modified St. Thomas cardioplegia plus 200 PM control EDP value of 10 mm Hg. adenosine (n = 9) or adenosine deaminase 15,5,2.5, or After 120 min of hypothermic ischemia and 45 min of 0.025 pg/ml of cardioplegia (n = 5, 5, 5, and 4, respec- reperfusion control hearts recovered to 51 f 3% of the tively) . preischemic DP. There was significantly better recovery Reperfusion was performed with perfusate tempera- of LV function in the adenosine-augmented hearts with ture at 37°C and delivered with pressure at 80 mm Hg. 68 + 7% recovery of DP in the hearts treated with 200 Defibrillation was performed as needed. During the ini- PM exogenous adenosine (P < 0.05 vs control hearts). tial 15 min of reperfusion, the intraventricular balloon However, the adenosine deaminase (ADA)-treated was kept deflated to simulate the beating, nonworking hearts had significantly worse recovery of function than condition. After the initial 15 min of reperfusion, the LV those of the control hearts. Hearts treated with 0.025 balloon was refilled to the preischemic control volume pg/ml ADA recovered to only 29 f 5% of preischemic DP and measurements of
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