ECTO-5'-NUCLEOTIDASE MEDIATES INFARCT SIZE-LIMITING EFFECT BY ISCHEMIC PRECONDITIONING IN THE RABBIT HEART

We examined whether ecto-5'-nucleotidase mediates infarct limitation b y ischemic preconditioning in the rabbit heart. Ecto-5'-nucleotidase a ctivity in ischemic region after ischemic preconditioning, was greater than that in nonischemic regions (23.6 +/- 2.5 vs. 13.6 +/- 1.0 nmol/ mg protein/min; p < 0.01). With an inhibitor of 5'-nucleotidase, alpha ,beta-methylene adenosine 5'-diphosphate (AMP-CP), ecto-5'-nucleotidas e activity in the ischemic region was comparable to that in the nonisc hemic region. Mean blood pressure was reduced from 73 +/-: 2 to 62 +/- +/- 3 mm Hg with intravenous AMP, whereas it did not change with cope rfusion of AMP and AMP-CP, suggesting effective inhibition of ecto-5'- nucleotidase. Separately, myocardial infarction was created by 30-min coronary occlusion and 3 h of reperfusion. Infarct size expressed as p ercentage volume in risk area was reduced by ischemic preconditioning compared with that in the control (7.8 +/- 2.5% vs. 38.1 +/- 4.0%; p < 0.01), However, infarct size in the group given AMP-CP plus ischemic preconditioning was similar to that in the control (36.2 +/- 2.8% vs. 38.1 +/-: 4.0%; NS), suggesting that ecto-5'-nucleotidase mediates inf arct limitation by ischemic preconditioning in the rabbit.