Extravascular adenosine influences endothelium-derived nitric oxide release from perfused dog semitendinosus artery

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Abstract
We tested the hypothesis that extravascular adenosine induces the release of vasodilatory products from endothelial cells lining skeletal muscle vessels. Endothelium-intact (n = 35) and -denuded (n = 5) dog semitendinosus intramuscular arteries were isolated, cannulated, and placed in 100-mL baths containing Krebs-Henseleit bicarbonate buffer (Krebs) at 37°C and gassed with 95% O2 - 5% CO2. Each vessel, as well as a parallel tubing segment (avascular control), was perfused at 3.5 ± 0.2 mL/min (inflow pressure 94 ± 2 mmHg; 1 mmHg = 133.3 Pa) with Krebs containing 100 µM phenylephrine, 6% dextran, and 15 units/mL superoxide dismutase. Perfusate from all segments dripped onto endothelium-denuded dog femoral artery rings. The addition of 10 µM acetylcholine to the perfusate to test the functional integrity of endothelium-intact donor segments did not alter resistance in vessel segments or change force in rings. The addition of 100 µM adenosine to the extravascular bath decreased resistance 1.5 ± 0.4 mmHg ·mL-1 ·min-1 in vessel segments but was without effect on downstream rings. When acetylcholine was retested in the presence of extravascular adenosine, a relaxation (16 ± 6%) occurred in rings receiving perfusate from endothelium-intact segments but not endothelium-denuded or tubing segments. This relaxation was eliminated by N omega -nitro-L-arginine (10 µM), a nitric oxide synthase inhibitor, and was attenuated to 4 ± 1% by 8-phenyltheophylline (10 µM), an adenosine receptor antagonist. Thus adenosine, in conjunction with acetylcholine, acting through a receptor-mediated event, resulted in the release of nitric oxide from the endothelium of perfused intramuscular arteries, indicating the potential for extravascular conditions to influence the release of endothelium-derived products.Key words: acetylcholine, adenosine, endothelium-dependent relaxation, nitric oxide, perfused intramuscular artery.

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