Investigating the Effect of Experimental Hypothyroidism on Insulin/Thyroid Hormones and Hepatic Steatosis

The close physiological and biochemical relationships between insulin/thyroid hormones and intermediary metabolism, as well as hepatic homeostasis, are well documented. Apart from significant changes in thyroid hormones levels and altered insulin secretion or resistance, there is no consistency regarding the presence of hepatic storage diseases and fatty liver in hypothyroid patients. The main objective of the current study was to evaluate the effect of experimental hypothyroidism on insulin level and histological alterations in the liver such as changes in lipid and glycogen reservoirs. In this study, 20 adult male Wistar rats were assigned to two similar groups including control and hypothyroid. Experimental hypothyroidism was induced by 0.02% propylthiouracil (PTU) administered to rats via drinking water for two months. The rates were then killed and blood samples were assayed for TSH, T4, T3, insulin hormones, and lipid profile. The left lobes of rats’ livers were also used for the histological study. Our results indicated that the two-month administration of 0.02% PTU induced mild hypothyroidism associated with about a 50% reduction in the insulin level. The examination of liver samples showed that there were no significant changes in the overall architecture of liver tissue as compared to normal controls; that is, hepatocytes morphology, appearance, and position of the core, as well as glycogen content, were the same. The main finding of the current work was that in the hypothyroid group, the mild steatosis was accompanied by dyslipidemia. Based on our findings, a two-month administration of 0.02% PTU induces mild hypothyroidism in rates associated with a 50% decrease in the insulin level and mild steatosis in liver hepatocytes. This condition in long period may predispose hypothyroid individuals to develop diabetes mellitus and fatty liver simultaneously.