Chilian W M, Layne S M, Eastham C L, Marcus M L
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City.
Circ Res. 1987 Nov;61(5 Pt 2):II47-53.
This study was designed to examine the hypothesis that epinephrine has nonuniform effects on coronary microvascular diameters. Measurements of coronary microvascular diameter were completed in anesthetized, open-chest cat preparations in which the epicardial microcirculation was viewed through an intravital microscope using stroboscopic epi-illumination. Images of coronary microvessels were digitized and analyzed on a video monitor. With arterial pressure controlled, measurements in the absence and presence of beta-adrenergic blockade (propranolol 1 mg/kg) were obtained during epinephrine infusion (1-2 micrograms/kg/min). In the absence of beta-adrenergic blockade, epinephrine produced a 25% increase in myocardial perfusion. Under these conditions, coronary vasodilation was observed in all classes of coronary arterial and arteriolar vessels. In the presence of beta-adrenergic blockade, epinephrine produced a significant decrease in myocardial perfusion (-20%). Nonuniform effects on diameter were observed in arterial and venous segments of the coronary circulation. These data are consistent with the view that in the absence of beta-adrenergic blockade, the functional coronary hyperemia associated with epinephrine administration is produced by uniform coronary arterial and arteriolar dilation. In the presence of beta-adrenergic blockade, with metabolic effects controlled, epinephrine produced a decrease in myocardial perfusion, which is related to a nonuniform decrease in coronary microvascular diameters. Such heterogeneous effects on microvascular diameters result in a redistribution of coronary microvascular resistance.
