A Study On The Relationship Between Thyroid Hormone And Remodeing Of Atrium And Ventricle

Objective: To investigate the relationship between thyroid hormone and remodeling of atrium and ventricle, and to explore the pathogenesis of hyperthyroid cardiopathy.Methods: Twenty New Zealand rabbits were randomly divided into control group and experimental group, and the number of each group was ten. Hyperthyroid cardiopathy animal model was established by peritoneal injection of Levothyroxine (L-Thy). All rabbits were followed up for 4 weeks. Heart rate, body weight, body temperature and blood samples were obtained at baseline and 7 days interval. The levels of serum TT3 and TT4 were measured with radioimmunoassays (RIAs). All rabbits underwent echocardiography, and LAD, LVD, thickness of IVS and LVPW were measured at baseline and the end of the 4th weeks. The ventricle, pulmonary vein muscle sleeves and posterior wall of atrium tissues were collected at the end of the 4th weeks. Cardiac weight index and cardiocyte diameter were measured. Cardiocyte was observed under light microscope. Myocardial fibrosis was displayed by VG stain, and collagen volume fraction(CVF) was measured using pathological image analytic system. Protein of Fas, FasL, MMP-2, MMP-9, TIMP-2, NGF in ventricle and protein of Fas, TH, GAP-43 in atrium and pulmonary vein muscle sleeves were localized by immunohistochemistry, and were semi-quantified with pathological image analytic system. mRNA expression of GAP-43 and TH in atrium and pulmonary vein muscle sleeves was semi-quantified with RT-PCR. Results: In experimental group, heart rate and body temperature increased, and body weight decreased. UCG showed that LAD, LVD, thickness of IVS and LVPW increased. Histological examination revealed remarkable myocardial hypertrophy, irregular array of cardiocyte and myocardium interstitial fibrosis. Protein expression of Fas, MMP-2, MMP-9, NGF in ventricular and that of Fas, TH, GAP-43 in atrium and pulmonary vein muscle sleeves increased, and that of TIMP-2 in ventricular decreased. mRNA expression of GAP-43 and TH in atrium and pulmonary vein muscle sleeves increased(P<0.05).Conclusions: L-Thy could induce myocardial hypertrophy, irregular array of cadiocyte, cadiocyte apoptosis, myocardium interstitial fibrosis and sympathetic nerve hyperplasia of atrium and pulmonary vein muscle sleeves. The system of Fas/FasL and matrix metalloproteinase may correlate with the onset of the hyperthyroid cardiopathy. The histological remodeling, sympathetic nerve remodeling and cell apoptosis of atrium and pulmonary vein muscle sleeves may be correlate with the onset of the hyperthyroid cardiopathy.