Raising aortic pressure via methoxamine injection resulted in a significantly smaller peak hyperemic flow increment compared to aortic constriction, due to alpha-stimulated coronary vasoconstriction.
Does raising aortic pressure via alpha-adrenoceptor stimulation reduce coronary flow reserve compared to mechanical aortic constriction in anesthetized dogs?
Coronary flow reserve increases proportionally with a rise in aortic pressure, but this increment is blunted when the pressure rise is mediated by alpha-adrenoceptor stimulation due to concurrent coronary vasoconstriction.
In order to investigate the effect of a rise in aortic pressure on coronary flow reserve and also on the difference of its effect according to the methods used to raise aortic pressure, this experiment was performed. Using 7 anesthetized dogs with heart rate held constant by a pacemaker, both the resting and the peak reactive hyperemic left circumflex coronary flow were measured following raising of the aortic pressure by either descending thoracic aorta constriction or methoxamine injection. The resting and peak reactive hyperemic coronary flows both increased linearly following the rise in aortic pressure. The magnitude of the resting flow increment and the resting coronary vascular resistance following raising aortic pressure did not differ significantly between the two different methods. However, the magnitude of the peak hyperemic flow increment and the peak hyperemic coronary vascular resistance following raising aortic pressure were significantly smaller with methoxamine injection than with aortic constriction. These data indicate that coronary flow reserve increases proportionally with a rise in aortic pressure. However, the magnitude of the increment of coronary flow reserve is smaller following an alpha-adrenoceptor-mediated rise in aortic pressure, because the maximal coronary vasodilation was reduced by alpha-stimulated coronary vasoconstriction.
Ohtsuka et al. (Thu,) conducted a other in Anesthetized dogs (n=7). Raising aortic pressure by methoxamine injection vs. Raising aortic pressure by descending thoracic aorta constriction was evaluated on Resting and peak reactive hyperemic left circumflex coronary flow. Raising aortic pressure via methoxamine injection resulted in a significantly smaller peak hyperemic flow increment compared to aortic constriction, due to alpha-stimulated coronary vasoconstriction.