Evidence that cytosolic and ecto 5 '-nucleotidases contribute equally to increased interstitial adenosine concentration during porcine myocardial ischemia

The purpose of this study was to determine the roles of cytosolic and ecto 5'-nucleotidase in myocardial ischemia-induced increases in interstitial fl uid (ISF) adenosine. Pentobarbital anesthetized, open chest pigs were instr umented with two microdialysis fibers in the distally perfused bed of the l eft anterior descending (LAD) coronary artery to estimate ISF metabolites. Fibers in control hearts were perfused with standard Krebs buffer. In two a dditional groups, after collecting one dialysate sample with normal Krebs, fibers were perfused with buffer supplemented with either L-homocysteine th iolactone (5 mM) or the ecto 5'-nucleotidase inhibitor alpha, beta-methylen e adenosine 5'-diphosphate (AOPCP, 5 mM). Hearts were then submitted to 60 minutes LAD occlusion and two hours reperfusion. Dialysate nucleosides and AMP were measured by high performance liquid chromatography The local deliv ery of homocysteine did not alter preischemic dialysate adenosine concentra tion (0.30 +/- 0.04 mu M) compared to pre-homocysteine infusion (0.39 +/- 0 .04 mu M) or control hearts (0.36 +/- 0.04 mu M), but AOPCP significantly d ecreased preischemic dialysate adenosine levels (from 0.36 +/- 0.02 to 0.14 +/- 0.03 mu M). During LAD occlusion both homocysteine and AOPCP reduced d ialysate levels by approximately 50%. At 30 minutes ischemia dialysate aden osine concentrations were 19.47 +/- 2.72, 11.41 +/- 2.44, and 7.93 +/- 1.01 mu M in control, homocysteine, and AOPCP hearts, respectively. AOPCP signi ficantly increased dialysate AMP levels; at 60 minutes ischemia AMP levels were 6.22 +/- 2.97 mu M in control hearts and 38.60 +/- 5.69 mu M in AOPCP treated hearts. These results suggest that both cytosolic and ecto 5'-nucle otidase contribute to ischemia-induced increases in ISF adenosine in porcin e myocardium.