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Effect of administration of physiological doses of thyroid hormone on cardiac remodeling in rats with myocardial infarction

Thyroid hormones modulate cardiovascular function in physiological and pathological conditions. In heart failure (HF), there is a decrease in serum levels of triiodothyronine (T3). The aim of this study was to determine whether delayed treatment with physiological dose of T3 attenuates cardiac remodeling in rats with chronic heart failure. HF was induced by myocardial infarction (MI). Animals subjected to simulated surgery were used as controls (Sham, n=12). Four months after surgery, infarcted rats were divided into two groups: untreated MI (n=11) and MI/T3 (MI treated with triiodothyronine, 0.5 μg/100 g body weight, n=11). Four and six months after surgery, rats were subjected to echocardiogram. There was no difference in echocardiographic variables between MI and MI/T3 groups before treatment. Infarct size was similar between groups (p>0.05, t test). Left atrial diameter was higher in MI than Sham group (Sham 12.0±1.54; MI 15.0±3.46; MI/T3 13.6±2.53 mm/kg; p<0.05). Isovolumic relaxation time normalized to heart rate was higher in MI (Sham 59.4±10.0; MI 73.2±9.7; MI/T3 60.9±9.1; p<0.05) and E‐wave deceleration time was lower in MI (Sham 48.6±4.86; MI 28.7±4.24; MI/T3 44.9±9.53 ms; p<0.05) than the other groups. In conclusion, late administration of triiodothyronine attenuates cardiac remodeling and preserves diastolic function in rats with myocardial infarction.