Adiponectin levels and some risk factors for atheroscelerosis in rats with experimental hypo-and hyperthyroidism

ABSTRACT

Adiponectin, an adipocyte-derived hormone, has been reported to decrease body weight by increasing thermogenesis and lipid oxidation. Also, has been reported to have anti-inflammatory and anti-atherogenic effects. Its relation to the metabolic changes and some cardiovascular risk factors in thyroid dysfunction states is still unclear. The aim of the present study was to evaluate adiponectin levels and its relation to metabolic and cardiovascular risk factors in rats with thyroid dysfunction. The study was carried out on 32 adult male Wi-star rats that were divided into 4 groups [8 rats each]. Group 1 included normal rats [Euthyroid], group 2 included rats treated with 0.03% methimazole in the drinking water for 28 days [hypothyroid rats], group Ill included rats injected subcutaneously with thyroxine [50 microg/100 g body weight] for 10 days [hyperthyroid rats], group IV included hypothyroid rats injected intraperitoneal with adiponectin [1.5 mg/kg body weight] for 7 days. Blood samples were collected at the end of experiments by decapitating the rats. The following parameters were measured serum adiponectin, serum T3, T4 and TSH levels, insulin level, fasting blood glucose, atherogenic indices [serum cholesterol, serum triglycerides, HDL-C, LDL-C, fibrinogen] and C-reactive protein. Insulin sensitivity was determined using the Homoestasis Model Assessment [HOMA-IR]. Serum adiponectin level in hyperthyroid rats was 2.9 fold higher than that of euthyroid [P<0.0001], while that in hypothyroid rats tended to be lower [20%] but without statistical significance. Serum adiponectin had a positive correlation with serum thyroxine and negative association with serum TSH [P<0.05]. Also, adiponectin levels correlated negatively with body weight. In the hypothyroid group adiponectin level correlated negatively with HOMA-IR [P<0.05]. There was a significant correlation between adiponectin and HDL-C, and CRP in both hypo- and hyperthyroid rats. Adiponectin administration produced significant decrease in cholesterol, triglycerides and low density lipoprotein cholesterol [LDL-C] and significant increase in HDL-C in hypothyroid rats. The results of our study demonstrated that, in rats; thyroid hormone disturbances modified serum adiponectin concentration and there was a significant relationship between adiponectin level and high density lipoprotein-cholesterol. Also, there is a possible role for adiponectin in cardiovascular protection through its effects on low grade inflammation and insulin resistance in cases of thyroid disorders