Thyroid Hormone and Myocardial Metabolism after Heart Surgery in Dogs

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 myocardi...