The purpose of this study was to determine the roles of cytosolic and ecto
5'-nucleotidase in
myocardial ischemia-induced increases in interstitial fluid (ISF)
adenosine.
Pentobarbital anesthetized, open chest pigs were instrumented with two microdialysis fibers in the distally perfused bed of the left anterior descending (LAD) coronary artery to estimate ISF metabolites. Fibers in control hearts were perfused with standard Krebs
buffer. In two additional groups, after collecting one
dialysate sample with normal Krebs, fibers were perfused with
buffer supplemented with either L-
homocysteine thiolactone (5 mM) or the ecto
5'-nucleotidase inhibitor
alpha, beta-methylene 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 delivery of
homocysteine did not alter preischemic
dialysate adenosine concentration (0.30 +/- 0.04 microM) compared to pre-
homocysteine infusion (0.39 +/- 0.04 microM) or control hearts (0.36 +/- 0.04 microM), but
AOPCP significantly decreased preischemic
dialysate adenosine levels (from 0.36 +/- 0.02 to 0.14 +/- 0.03 microM). During LAD occlusion both
homocysteine and
AOPCP reduced
dialysate levels by approximately 50%. At 30 minutes
ischemia dialysate adenosine concentrations were 19.47 +/- 2.72, 11.41 +/- 2.44, and 7.93 +/- 1.01 microM in control,
homocysteine, and
AOPCP hearts, respectively.
AOPCP significantly increased
dialysate AMP levels; at 60 minutes
ischemia AMP levels were 6.22 +/- 2.97 microM in control hearts and 38.60 +/- 5.69 microM in
AOPCP treated hearts. These results suggest that both cytosolic and ecto
5'-nucleotidase contribute to
ischemia-induced increases in ISF
adenosine in porcine myocardium.