EARLY TREATMENT OF OBESE (OB/OB) MICE WITH TRIIODOTHYRONINE INCREASES OXYGEN-CONSUMPTION AND TEMPERATURE AND DECREASES BODY-FAT CONTENT

An early abnormality in the ob/ob mouse is a low circulating level of the thyroid hormone, triiodothyronine (T-3). The possibility was explored that early T-3 treatment of ob/ob mice will increase oxidative metabolism and lower body fat content. Doses of T-3, ranging from 0.0 to 25.0 mu g/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 (T-4), T-3, insulin and glucose, oxygen consumption, colonic temperature, and body composition were analyzed. T-3 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. T-3 treatment also increased serum T-3, and decreased serum T-4, insulin, and glucose concentrations in ob/ob mice. Because total body protein did not change as a result of T-3 treatment, the Increased oxidative metabolism due to T-3 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.