THE EFFECTS OF INTRAVENOUS CLONIDINE ON REGIONAL MYOCARDIAL-FUNCTION IN A CANINE MODEL OF REGIONAL MYOCARDIAL-ISCHEMIA

This study was performed to investigate the effects of clonidine on re gional myocardial function in a canine model of regional myocardial is chemia. Myocardial systolic shortening (%SS) was used as an index of r egional myocardial function. In eight dogs after thoracotomy, the left circumflex coronary artery (LCX) was occluded by screw clamp until re gional myocardial function became impaired. After partial occlusion of the LCX, cumulative doses of clonidine (1.25, 2.5, and 5.0 mu g/kg) w ere administered intravenously. After administration of clonidine, hea rt rate, mean arterial blood pressure (MAP), and norepinephrine concen tration decreased in a dose-dependent manner. At a dose of 5.0 mu g/kg of clonidine, the LCX flow and systolic shortening of the LCX area de creased to 76% and 81% of the poststenotic values (P < 0.05, respectiv ely), whereas no significant changes were observed at a dose of 1.25 a nd 2.5 mu g/kg. These results suggest that clonidine administration an d an associated decrease in arterial blood pressure deteriorates regio nal myocardial function of the ischemic myocardium.