Effect of long-term L-thyroxine treatment on the activity of NO-synthases in tissues of rats with obesity induced by high-fat diet

Abstract

Under obesity, a component of metabolic syndrome (MS), macro- and microcirculation are attenuated, which is associated with abnormalities of NO-dependent cascades and leads to pathology of the cardiovascular system. Among the activators of NO-synthases (NOS), the enzymes catalyzing NO synthesis, are thyroid hormones. Since obesity and MS are characterized by reduced functions, of the thyroid gland, the replacement therapy with thyroid hormones, possessing the properties of vasodilators, is one of approached to restore functioning of the cardiovascular system. However, data on influence of thyroid hormones on NOS activity in obesity are not currently available. The aim of this work was to study the effect of four-week treatment of rats with obesity induced by high-fat diet with L-thyroxine (at a daily dose of 20 mg-kg) on functional activity of total NOS, as well as one endothelial (eNOS) and neuronal (nNOS) isoforms of the enzyme in the brain, myocardium and skeletal muscles of animals. In obese rats the decrease of thyroid hormones level, impaired glucose toleranse, and dyslipidemia were detected. In the myocardium and skeletal muscles of obese rats the activity of total NOS and eNOS was strongly decreased, whereas in the brain the activity of these enzymes was not significantly changed. Long-term treatment of obese rats with thyroxine led to a significant increase in activity of total NOS and eNOS in the myocardium and skeletal muscles and to an increase in activity of total NOS and nNOS in the brain, with the enzyme activity exceeding that in control. In healthy animals treated with thyroxine a significant increase in activity of total NOS and eNOS in the myocardium and skeletal muscles and in activity of total NOS in the brain was also eNOS in the myocardium and skeletal muscles and in activity of total NOS in the brain was also found. A significant contribution to the increasing activity of total NOS in obese rats and healthy animals treated with thyroxine belonged to the inducible isoform of the enzyme whose activity was found by calculation. Thus, the four-week thyroxine treatment of obese rats with deficiency of thyroid hormones led to a complete restoration of activity of total NOS and eNOS, reduced in obesity, in the myocardium and skeletal muscles which indicated the prospects of thyroxine therapy for treatment of vascular pathology in obesity and MS.