Effect of gossypol on thyroid hormones in young female rats

The study was designed to examine the effect of gossypol on thyroid function in young female rats. Forty young Sprague-Dawley female rats were randomly assigned to four treatment groups. The dosages of gossypol acetic acid (gossypol) used for this experiment were 1, 5 and 10 mg/kg body weight/day in 0.5 ml potassium phosphate buffer subcutaneously started from day 34 of age for 15 consecutive days. The control group was treated with vehicle alone. Animals were sacrificed 15 days after gossypol treatment. Blood samples and sera were collected and prepared for measurement of thyroid hormones by radioimmunoassay. The levels of free thyroxine (T4), 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (reverse T3, rT3) in control rats at age 49 days averaged 55.90 +/- 7.7, 670 +/- 90, and 71.7 +/- 5.7 pg/ml of serum, respectively. Fifteen days after gossypol treatment at 5 and 10 mg/kg/day, the free T4 levels significantly decreased to 21.96 +/- 2.1 and 11.12 +/- 1.5 pg/ml of serum, the T3 levels significantly decreased to 430 +/- 89, 359 +/- 90 pg/ml of serum and the rT3 levels were significantly decreased to 37.20 +/- 7.3, and 24.20 +/- 6.0 pg/ml of serum, respectively. However, the serum levels of free T4, T3 and rT3 in the 1 mg/kg/day of gossypol-treated animals were not significantly different from the controls. Five to 15 days after initiation of gossypol treatment, both body weight gain and food intake appeared to be significantly reduced at 5 and 10 mg/kg/day of gossypol treatment. This trend continued to the end of the 15-day gossypol treatment. The results provide new evidence that gossypol might have exerted its antithyroid function by an unknown mechanism that triggered an interference in body metabolism, thus causing the loss of food intake and body weight gain in young female animals.