Abstract
Recent studies have demonstrated that thyroid hormone improves hemodynamics following open-heart surgery, through unknown mechanisms. The effect of triiodothyronine on myocardial metabolism was studied in dogs undergoing normothermic crystalloid cardioplegic arrest. Seven animals in group 0 served as controls, 8 in group 1 received 0.1μg·kg−1·min−1 triiodothyronine intravenously after aortic cross-clamping, and 3 dogs in group 2 received triiodothyronine 150 μg per day orally for 7 days preoperatively and intravenously (0.1 μg·kg−1·min−1) after aortic cross-clamping. Myocardial carbon dioxide production and the uptake of oxygen, lactate, glucose, and free fatty acids were determined before aortic cross-clamping and at 10, 30, 60, and 120 minutes after declamping. After aortic cross-clamping, increased myocardial uptake of oxygen, lactate, and glucose were observed in group 1 compared with group 0. Myocardial free fatty acid uptake decreased in all groups. Carbon dioxide production correlated with myocardial oxygen uptake. These findings suggest that intraoperative triiodothyronine supplementation improves myocardial metabolism but preoperative administration is ineffective.
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