Interaction of methoxamine with compensatory vasodilation distal to coronary stenoses.

The interaction of alpha 1-receptor mediated vasoconstriction with the compensatory vasodilation distal to coronary stenoses was examined in 9 open-chest dogs. Stenoses on proximal circumflex artery were produced by a circumferential wire snare; an intermediate stenosis was defined by reduction of the reactive hyperemia repayment to 70%, a critical stenosis by prevention of any repayment following a 15-s occlusion. Methoxamine (Vasoxine), 500 micrograms, was infused via a small catheter distal to the stenosis under a constant coronary perfusion pressure of 80 mmHg and a constant heart rate of 160 bpm. The vasoconstrictive response to methoxamine correlated with the degree of reactive hyperemia repayment after 15 s occlusion (r = 0.74) and the preexisting level of poststenotic resistance (r = 0.62). At increasing peripheral coronary pressure distal to the stenosis the resistance of the stenosis was reduced (r = -0.84). Thus, alpha 1-adrenergic vasoconstriction is less marked with increasing compensatory vasodilation distal to coronary stenosis. The severity of the stenosis is reduced at increased intraluminal pressure, probably by distention of its luminal area. Methoxamine might induce a redistribution of coronary blood flow towards ischemic regions and reduce ischemic injury.