Clonidine improves recovery from myocardial stunning in conscious chronically instrumented dogs.

Unlabelled: Clonidine, an alpha2-adrenergic agonist, has been widely used in anesthesia because of its sedative, analgesic, sympatholytic, and specific hemodynamic effects. The use of clonidine in myocardial ischemia is controversial because of its bradycardic and hypotensive effects. In the present study, we tested the hypothesis that clonidine improves recovery from myocardial stunning in conscious dogs. Seven dogs were chronically instrumented to allow measurement of left atrial pressure (LAP), aortic blood pressure (ABP), left ventricular pressure (LVP), maximal rate of increase of LVP (LVdP/dtmax), and myocardial wall thickening fraction (WTF). The myocardial blood flow was measured using colored microspheres. To compensate for any potential interaction between the two ischemic episodes, experiments were performed on separate days in a cross-over fashion (four animals underwent Condition 1, and three underwent Condition 2 as their first experiment). The ischemic episodes involved 1) 10 min of ischemia of the left anterior descending (LAD) coronary artery without any intervention, and 2) 10 min of LAD ischemia 30 min after 10 microg/kg iv clonidine. WTF was measured before the induction of ischemia or the application of clonidine (baseline) and at predetermined time points until complete recovery of myocardial function. WTF recovered faster during the first 2 h of reperfusion when clonidine was administered. The increase in plasma epinephrine was attenuated by clonidine during ischemia, but there was no change during reperfusion. The increase of plasma norepinephrine levels was attenuated during ischemia and reperfusion. The hemodynamic effects of clonidine did not depress myocardial perfusion or impair myocardial function.

Implications: In this study, we investigated the effects of IV clonidine on myocardial stunning in chronically instrumented dogs. Clonidine improved the recovery from myocardial stunning and attenuated increases in catecholamine plasma levels.