Eight weeks of L-thyroxine treatment in rats following myocardial infarction significantly improved left ventricular +dp/dt and increased total LV tissue area by 34% compared to untreated MI rats.
Does L-thyroxine treatment improve left ventricular remodeling in adult female Sprague-Dawley rats after myocardial infarction?
Eight weeks of L-thyroxine treatment in rats post-myocardial infarction improved left ventricular hemodynamics and cellular remodeling in the non-infarcted area.
Absolute Event Rate: 8862% vs 6768%
p-value: p=<0.05
BACKGROUND: Left ventricular (LV) remodeling following large transmural myocardial infarction (MI) remains a pivotal clinical issue despite the advance of medical treatment over the past few decades. Identification of new medications to improve the remodeling process and prevent progression to heart failure after MI is critical. Thyroid hormones (THs) have been shown to improve LV function and remodeling in animals post-MI and in the human setting. However, changes in underlying cellular remodeling resulting from TH treatment are not clear. METHODS: MI was produced in adult female Sprague-Dawley rats by ligation of the left descending coronary artery. L-thyroxine (T4) pellet (3.3 mg, 60 days sustained release) was used to treat MI rats for 8 weeks. Isolated myocyte shape, arterioles, and collagen deposition in the non-infarcted area were measured at terminal study. RESULTS: T4 treatment improved LV ±dp/dt, normalized TAU, and increased myocyte cross-sectional area without further increasing myocyte length in MI rats. T4 treatment increased the total LV tissue area by 34%, increased the non-infarcted tissue area by 41%, and increased the thickness of non-infarcted area by 36% in MI rats. However, myocyte volume accounted for only ~1/3 of the increase in myocyte mass in the non-infarct area, indicating the presence of more myocytes with treatment. T4 treatment tended to increase the total length of smaller arterioles (5 to 15 μm) proportional to LV weight increase and also decreased collagen deposition in the LV non-infarcted area. A tendency for increased metalloproteinase-2 (MMP-2) expression and tissue inhibitor of metalloproteinases (TIMPs) -1 to -4 expression was also observed in T4 treated MI rats. CONCLUSIONS: These results suggest that long-term T4 treatment after MI has beneficial effects on myocyte, arteriolar, and collagen matrix remodeling in the non-infarcted area. Most importantly, results suggest improved survival of myocytes in the peri-infarct area.
Chen et al. (Thu,) conducted a other in Myocardial Infarction (n=68). L-thyroxine (T4) vs. Placebo pellet was evaluated on Left ventricular maximal rate of pressure development (+dp/dt) (p=<0.05). Eight weeks of L-thyroxine treatment in rats following myocardial infarction significantly improved left ventricular +dp/dt and increased total LV tissue area by 34% compared to untreated MI rats.