AJP - Heart and Circulatory Physiology, Vol 251, Issue 3 554-H561, Copyright © 1986 by American Physiological Society
Reactive dilation and late-hyperemic constriction of epicardial coronary artery after short coronary occlusion
H. Yamamoto, H. Tomoike, K. Hisano, T. Inoue, M. Mohri and M. Nakamura
Coronary blood flow and epicardial coronary artery diameter were
simultaneously measured by an electromagnetic or Doppler flow probe and a
pair of ultrasonic crystals, respectively, during reactive hyperemia in
conscious dogs. Reactive dilation appeared after the full appearance of
reactive hyperemia and lasted for a period of 4-20 times the duration of
the coronary occlusion. beta-Receptor blockade (propranolol, 1 mg/kg iv)
attenuated both the reactive hyperemia in volume by 21-22% (P less than
0.01) and dilative responses of the epicardial coronary diameter by 27-28%
(P less than 0.01), despite a nonsignificant attenuation of the resting or
peak hyperemic coronary blood flow. When coronary blood flow was held
constant during reperfusion, by an occluder distal to the ultrasonic
crystals, the reactive dilation disappeared. A peculiar reactive
constriction was noted when coronary occlusion was performed proximal to
the site of the ultrasonic crystals. Appearance of this constriction was at
149 and 385 s after the release of 5 and 60 s of coronary occlusion,
respectively. This late reactive constriction disappeared after
pretreatment with alpha- (phentolamine, 1 mg/kg iv) and/or alpha- +
beta-blockade, but not with beta-blockade alone, and it was not observed
when the coronary diameter was measured proximal to the occluder. Thus
reactive dilation of the epicardial coronary artery derives from an
increase in coronary flow and is reduced by propranolol via a reduction in
the hyperemic flow, suggesting a flow-dependent change in the diameter of
the epicardial coronary artery. Reactive constriction is a local phenomenon
following marked reduction in the coronary diameter and is abolished by
alpha-adrenergic blockade with phentolamine.
