Efeito do agonista seletivo do receptor β tireoidiano (GC-1) na tolerância ao esforço de ratos wistar submetidos ao hipotireoidismo experimental

Abstract

INTRODUCTION: Thyroid hormone (TH) has a central role in metabolic homeostasis acting on lipolysis and cholesterol control. However, HT has profound effects on the heart by its receptor α1. Thus , selective β thyroid agonists such as GC-1 , that has proven action on the metabolic rate , serum cholesterol levels and lipolysis without affecting heart rate, presented with great therapeutic value to fight diseases such as obesity and dyslipidemia. However, no study to date sought to test the action of this substance in the organism undergone physical effort. AIM: Investigate the effect of GC-1 on tolerance to exercise in rats with experimental hypothyroidism. MATERIALS AND METHODS: Six groups with eight animals were studied: control group (C), hypothyroid group without treatment (HYPO); hypothyroidism treated with T 4 1x (T 4) or 10 times higher (10×T4); hypothyroidism treated with equal molar doses of GC-1 (GC-1) or 10 times higher (10×GC-1). After eight weeks, each animal underwent an exercise tolerance test by measuring the time (seconds), in which the rats were swimming with a load attached to their tails without being submerging for more than 10 sec. After the test, the animals were euthanized, and blood samples were collected for biochemical analysis, and the heart and soleus muscle were removed for weighing and morphometric analysis of the cardiomyocyte. RESULTS: Hypothyroidism significantly reduced tolerance to exercise and, treatment with GC-1 1× or T 4 recover tolerance test to normal parameters. However, high doses of T 4 also decreased tolerance to physical exercise. Conversely, ten times higher doses of GC-1 did not impair tolerance to exercise. Interestingly, hypothyroidism, treated or not with T 4 , GC-1 or even high doses of GC-1 (10x) did not change cardiomyocyte diameter and relative weight of the soleus muscle. In contrast, higher doses of T 4 significantly increased cardiomyocyte diameter and induced atrophy of the soleus muscle. CONCLUSION: Unlike T 4 , GC-1 in high doses did not modify tolerance to physical exercise in the rats with hypothyroidism.