The association of adverse health with high fat intake has long been recognized. However, the lack of research focusing on the interrelationship of thyroid and liver function, and the pathogenesis of a high fat diet leaves these topics poorly understood. The objective of this study was to evaluate and compare the physiological changes in euthyroid and thyroid altered animal model fed saturated and unsaturated high fat diets. To achieve this objective adult male Sprague Dawley rats (n = 100) were fed one of five diets; a control or one of four test diets containing 25% saturated or unsaturated, and 37% saturated or unsaturated fats for a period of eight weeks. Each experimental group consisted of ten euthyroid and ten thyroid altered animals. An altered thyroid state was chemically induced with the addition of 0.05% propylthiouracil (PTU) in the drinking water. Euthyroid animals fed high fat diets increased in body weights and body lengths, compared to thyroid altered animals (P < 0.05). Alanine aminotransferase (ALT) and asparte aminotransferase (AST) levels increased across all experimental groups. HbA1C values and urinary glucose values were within normal range for all animals. Liver morphology showed increased hepatic stellate (ito) and vacuole cells in thyroid altered animals. These findings suggest that altered thyroid status negatively impacts growth and weight gain, and simultaneously affected lipid metabolism, resulting in abnormal liver morphology.

The thyroid hormones (THs) play critical roles in differentiation, growth and metabolism and are critical for the normal function of nearly all tissues, with major roles in regulating energy balance, metabolism of glucose, and lipids and metabolic rate. The two functionally different types of fat in mammals are: brown adipose tissue (BAT), containing specialized thermogenic brown adipocytes, and white adipose tissue (WAT), containing white adipocytes specialized in triglyceride metabolism. Both tissues are strongly involved in energy balance. The objective of this study was to evaluate and compare physiological and histological effects of saturated and unsaturated fats in periadrenal BAT and thyroid gland of euthyroid and thyroid altered rats. Adult male Sprague Dawley rats (n=100) were exposed to a control or one of four test diets; 25% and 27% (saturated or unsaturated) for 8 weeks. A chemically reduced thyroid state was obtained through the addition of .05% propylthioracil (PTU) in drinking water. The body weights of the normal animals were significantly higher than in the altered thyroid groups. Histopathological evaluations confirmed damage to thyroid tissue in the altered thyroid groups and revealed an increase in BAT to WAT conversion in the thyroid gland and periadrenal BAT. Gene expression of FABP and LXR was generally higher in thyroid altered animals compared to the euthyroid group. In conclusion, chemically induced hypothyroidism negatively impacted fat metabolism, which contributed to increased BAT to WAT conversion and increased expression of FABP and LXR.