1995 Volume 18 Issue 7 Pages 951-956
We investigated the effects of selective β1 adrenoceptor stimulation on oxygen tension (pO2) in the myocardium of anesthetized dogs. A β1-selective full agonist, T-0509 (0.01-0.05μg/kg, i. v.), caused positive inotropic and chronotropic effects, and increased left circumflex blood flow, although it did not change arterial blood pressure. These effects were inhibited by bisoprolol (10μg/kg), but not by ICI 118551 (30μg/kg). Under control conditions, subepicardial pO2 (pO2epi) and subendocardial pO2 (pO2endo) were approximately 33 and 27 mmHg, respectively. T-0509 (0.05μg/kg) decreased pO2epi in all cases, with a mean decrease of 2.6±0.5mmHg, and this was significantly inhibited by bisoprolol. T-0509 caused an increase (7 out of 10 dogs) or a slight decrease (3 out of 10) in the pO2endo; the mean increment was 2.0±1.3mmHg (n=10). Isoproterenol (0.01-0.05μg/kg, i. v.) exerted positive inotropic and chronotropic effects that were sensitive to bisoprolol, and a hypotensive effect that was sensitive to ICI 118551. Isoproterenol caused an increase in blood flow that was sensitive to ICI 118551. Isoproterenol (0.05μg/kg) decreased pO2epi in all cases, with a mean decrease of 2.7±0.5mmHg, which was significantly inhibited by bisoprolol. Isoproterenol caused an increase (5 out of 10) or a slight decrease (5 out of 10) in the pO2endo; the mean increment was 1.1±1.2mmHg (n=10). These results suggest that, while coronary arteries dilate during selective stimulation of β1-adrenoceptors or nonselective stimulation of β-adrenoceptors, the oxygen supply is insufflcient in pO2epi due to a marked increase in oxygen demand. However, pO2endo does not readily decrease under these conditions.