Evidence for Direct Control of Coronary Vascular Tone by Oxygen

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Abstract
The interaction between the effects of oxygen and adenosine on acetylcholine-induced contractile tension was observed in helical coronary arterial strips suspended in physiological salt solution. It was found that (1) steady-state contractile tension was unaffected or depressed 5-20% when oxygen pressure (Po 2 ) was diminished to levels as low as 5-10 mm Hg, (2) contractile tension was markedly depressed at a Po 2 of 0 mm Hg, (3) adenosine-induced relaxation of contractile tension was inversely proportional to Po 2 in the tissue bath, and (4) in the presence of adenosine at a concentration just adequate to inhibit contractile tension at a Po 2 of 10 mm Hg, contractile tension was directly proportional to bath Po 2 . The latter two observations were usually most apparent at a Po 2 between 10 and 40 mm Hg. It is proposed that the vasodilating effect of adenosine on the intact coronary vasculature may be most effective during myocardial hypoxia and that physiological control of coronary vascular tone may be more closely related to variations in local Po 2 than to variations in local concentrations of adenosine.