Direct Vasomotor Effects of Isoflurane in Subepicardial Resistance Vessels from Collateral-dependent and Normal Coronary Circulation of Pigs

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Abstract
Background: The purpose of the current investigation was to determine and compare the direct effect of isoflurane on normal resistance coronary arteries and similarly sized coronary arteries in collateral-dependent (CD) circulation. A differential vasomotor effect of isoflurane might contribute to flow redistribution, either adverse or favorable, between normal and CD regions. Methods: The authors used a swine model of chronic coronary occlusion. Six weeks after ameroid occluder placement around the left circumflex artery, the heart was removed. Myocardial blood flow, measured in vivo before the removal, was lower during rapid atrial pacing in the CD region than in the normally perfused region. These in vivo studies established the existence and location of CD circulation. Subepicardial microvessels, measuring approximately 100 microns, were dissected from both the CD region and the normal region. Either with or without preconstriction of the vessels with the thromboxane analogue U46619 1 microM, direct vasomotor effect of isoflurane was examined in vitro by video microscopy. In addition, vasomotor responses to endothelin-1, the endothelium-dependent dilator adenosine 5' diphosphate, and the endothelium-independent dilator sodium nitroprusside were compared between CD and normal resistance vessels. Results: Isoflurane caused greater concentration-dependent constriction of the normal vessels than of the CD vessels (P < 0.05); this constrictive effect was masked by preconstriction of the vessels. Vasodilation of ADP was less in CD vessels than in normal vessels (P < 0.001), but vasodilation to sodium nitroprusside was not significantly different (P = 0.45). Vasoconstriction to endothelin-1 was greater in CD vessels than in normal vessels (P < 0.01). Conclusions: The vasoconstrictive effect of isoflurane normally observed in coronary resistance vessels is impaired in resistance vessels that supply a CD area. The basis of this may be related to endothelial dysfunction.