CORONARY VASCULAR EFFECTS OF DEXMEDETOMIDINE DURING REACTIVE HYPEREMIA IN THE ANESTHETIZED DOG

Objective: The central sympatholytic effects of alpha(2)-adrenergic ag onists are believed to be beneficial during myocardial ischemia, but t he peripheral vasoconstrictive effects are controversial. The aim of t his study was to investigate the coronary vascular effects of dexmedet omidine (DM) during reactive hyperemia. Design: The study had a prospe ctive, randomized, open-comparative design. Setting: University animal laboratory. Participants: Nine mongrel dogs. Interventions: Coronary artery occlusions lasting 2 minutes were induced five times at 40-minu te intervals. DM, 0.1, 1, and 10 mu g/kg was administered 15 minutes b efore the second, third, and fourth coronary occlusion, respectively. The alpha(2)-antagonist atipamezole was administered before the fifth coronary occlusion. Measurements and Main Results: DM, 1 mu g/kg, sign ificantly decreased heart rate (from 128 +/- 13 to 96 +/- 21 beats/min ); 10 mu g/kg of DM also significantly decreased cardiac output (from 3.4 +/- 1.1 to 1.4 +/- 0.4 L/min). DM decreased myocardial blood flow in all layers of normally perfused myocardium. In hyperemic myocardium , DM significantly decreased epicardial blood flow (from 3.30 +/- 1.43 to 1.44 +/- 0.49 mL/min/g after DM 10 mu g/kg), whereas endocardial b lood flow did not change, hereby significantly increasing the endo/epi blood flow ratio (from 0.99 +/- 0.54 to 2.28 +/- 0.78). Conclusions: In the postischemic hyperemic subendocardial layer, coronary blood flo w was preserved after DM. DM reduced primary determinants of myocardia l oxygen demand. These effects of DM may be beneficial in conditions o f temporary coronary artery occlusion and subsequent reperfusion. Copy right (C) 1996 by WB. Saunders Company