Ischemia/reperfusion and
hypoxia/reoxygenation of the heart both induce shedding of the coronary endothelial glycocalyx. The processes leading from an
oxygen deficit to shedding are unknown. An involvement of resident perivascular cardiac mast cells has been proposed. We hypothesized that either
adenosine or
inosine or both, generated by
nucleotide catabolism, attain the concentrations in the interstitial space sufficient to stimulate A3 receptors of mast cells during both
myocardial ischemia/reperfusion and
hypoxia/reoxygenation. Isolated hearts of guinea pigs were subjected to either normoxic perfusion (
hemoglobin-free
Krebs-Henseleit buffer equilibrated with 95%
oxygen), 20 minutes hypoxic perfusion (
buffer equilibrated with 21%
oxygen) followed by 20 minutes reoxygenation, or 20 minutes stopped-flow
ischemia followed by 20 minutes normoxic reperfusion (n = 7 each). Coronary venous effluent was collected separately from so-called transudate, a mixture of interstitial fluid and lymphatic fluid appearing on the epicardial surface.
Adenosine and
inosine were determined in both fluid compartments using high-performance liquid chromatography. Damage to the glycocalyx was evident after
ischemia/reperfusion and
hypoxia/reoxygenation.
Adenosine concentrations rose to a level of 1 μM in coronary effluent during hypoxic perfusion, but remained one order of magnitude lower in the interstitial fluid. There was only a small rise in the level during postischemic perfusion. In contrast,
inosine peaked at over 10 μM in interstitial fluid during
hypoxia and also during reperfusion, while effluent levels remained relatively unchanged at lower levels. We conclude that only
inosine attains levels in the interstitial fluid of hypoxic and postischemic hearts that are sufficient to explain the activation of mast cells via stimulation of A3-type receptors.