Early Treatment of Obese (ob/ob) Mice with Triiodothyronine Increases Oxygen Consumption and Temperature and Decreases Body Fat Content

Abstract

An early abnormality in the ob/ob mouse is a low circulating level of the thyroid hormone, triiodothyronine (T₃). The possibility was explored that early T₃ treatment of ob/ob mice will increase oxidative metabolism and lower body fat content. Doses of T₃, ranging from 0.0 to 25.0 μg/100 g body wt were injected, ip, Into ob/ob and non-ob/ob mice daily from 3 weeks until 6 weeks of age. Food intake was equalized across all groups to that consumed by non-ob/ob saline-treated group. At 6 weeks of age, body weight, serum concentrations of thyroxine (T₄), T₃, insulin and glucose, oxygen consumption, colonic temperature, and body composition were analyzed. T₃ treatment decreased body weight, increased body oxygen consumption, increased colonic temperature, and decreased body fat without a significant change in body protein in ob/ob mice. T₃ treatment also increased serum T₃, and decreased serum T₄, insulin, and glucose concentrations in ob/ob mice. Because total body protein did not change as a result of T₃ treatment, the increased oxidative metabolism due to T₃ treatment was probably via the change of metabolic activity of the total lean body mass or the specific metabolically active tissues in the ob/ob mice, such as brown adipose tissue, liver, or muscle.