Differential effects of selective beta 1-agonist stimulation on epi- and endocardial oxygen tension in anesthetized...

We investigated the effects of selective beta 1 adrenoceptor stimulation on oxygen tension (pO2) in the myocardium of anesthetized dogs. A beta 1-selective full agonist, T-0509 (0.01-0.05 microgram/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 (10 micrograms/kg), but not by ICI 118551 (30 micrograms/kg). Under control conditions, subepicardial pO2 (pO2 epi) and subendocardial pO2 (pO2endo) were approximately 33 and 27 mmHg, respectively. T-0509 (0.05 microgram/kg) decreased pO2epi in all cases, with a mean decrease of 2.6 +/- 0.5 mmHg, 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 +/- 1.3 mmHg (n = 10). Isoproterenol (0.01-0.05 microgram/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 (0.05 microgram/kg) decreased pO2epi in all cases, with a mean decrease of 2.7 +/- 0.5 mmHg, 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 +/- 1.2 mmHg (n = 10).(ABSTRACT TRUNCATED AT 250 WORDS)