Effects of iodine deficiency and iodine excess on rat myocardial histology and electrical activity

    LIU Guiª²Zhi1, ZHANG Zhao2, WU Yiª²Ming1, YE Zhenª²Kun3, CHEN Zuª²Pei3, YAN Yuª²Qin3

    1Department of Toxicology, College of Public Health,2Departª²ment of Physiology£¬Medical School, Zhengzhou University, Zhengzhou 450052, China, 3Institute of Endocrinology, Tianjin Medical University£¬Tianjin 300070, China

    ¡¾Abstract¡¿ AIM: To observe the effects of iodine deficiency and iodine excess on rat myocardial histology and electrical activity. METHODS: Ninety Wistar rats were divided into 6 groups at random: low iodine (LI), normal iodine (NI), 5ª²fold iodine (5HI), 10ª²fold iodine (10HI), 50ª²fold iodine (50HI) and 100ª²fold iodine group (100HI) respectively and all fed with water containing various concentrations of KIO3. At 3 and 6 months after iodine administration, the median of urinary iodine was measured. At 6 months after iodine administration, the level of thyroid hormone (TH) in serum was measured by means of chemoluminescence. The electrocardiogram (ECG), the heart weight to body weight ratio (H/B ratio) were recorded. The histopathological changes of left ventricular myocardium were observed with light microscope. RESULTS: As compared with NI groups, the median of urinary iodine and the level of serum TH were decreased (P<0.001) whereas H/B ratio was increased in LI group (P<0.001). The pathological changes of left ventricle were the increased inner diameter of left ventricular cavity, the decreased thickness of left ventricular free wall and the local necrosis. In response to various iodine treatment, the level of urinary iodine rose significantly with increasing concentration of iodine. Although the level of serum TH was not significantly changed in each iodine treatment group, there was a strong decreasing trend for serum TH among HI groups. The levels of TT3 declined in 10HI [(1.10¡À0.15) nmol/L], 50HI [(1.10¡À0.15) nmol/L] and 100HI [(1.18¡À0.15) nmol/L] groups compared with NI [(1.34¡À0.27) nmol/L] group (P<0.01, P<0.01 and P<0.05, respectively). The levels of TT4 went down only in 10HI [(45.60¡À9.85) nmol/L] and 50HI [(45.86¡À9.79) nmol/L] groups compared with NI group [(54.97¡À11.21) nmol/L] (P<0.05). In addition, wave patterns, intervals of ECG, H/B ratio and the histopathological changes of left ventricle were not significantly different among any HI groups (P>0.05). Only in 5HI and 100HI groups, local myocardial fibrosis of left ventricle was found. CONCLUSION: Iodine deficiency and iodine excess could induce hypothyroidism in normal rats and affect their myocardial histology and electrical activity. ......