Coronary alpha-adrenergic stimulation does not alter the heterogeneity of myocardial blood flow and oxygen...

Previous studies have suggested an uneven distribution of alpha-adrenergic receptors within the coronary arterial tree. We hypothesized that stimulation of these receptors would alter the regional and microregional variability of oxygen supply and utilization. Accordingly, we measured the heterogeneity of coronary blood flow to 0.5 g tissue samples and O2 saturation of small cardiac veins during coronary alpha-adrenergic stimulation. In 14 dogs we cannulated and perfused a branch of the left coronary artery. In seven dogs, an intracoronary infusion of the alpha-adrenergic agonist phenylephrine was established after prior beta-adrenergic blockade. Phenylephrine infusion decreased subendocardial venous O2 saturation (41.6 +/- 5.6 vs 45.4 +/- 5.8% saturated, P less than 0.05). It did not change the heterogeneity or distribution of the O2 saturations relative to the normally-perfused region (coefficient of variation = 22.4 +/- 6.7 vs. 19.7 +/- 4.8%, P = 0.20). Regional blood flows were made during control, beta-adrenergic blockade, and phenylephrine infusion conditions in the remaining dogs. The coefficient of variation of blood flow to samples from the perfused region was 27.1 +/- 9.8, 27.8 +/- 10.8, and 24.7 +/- 7.5% (P greater than 0.25), respectively. The results indicate that coronary alpha-adrenergic stimulation does not alter O2 supply/utilization heterogeneity, and suggest a fairly uniform distribution and/or effect of alpha-adrenergic receptors within the coronary resistance vessels.