The impact of dietary fat and thyroid function on adipose conversion in male Sprague Dawley rats (1160.10)

Abstract

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.