Effect of thyroxine injection on bone growth in energy deficient rats.

We investigated the role of thyroxine on bone growth in energy deficient rats. Rats were fed a normal diet and injected with saline, or a low-energy diet and injected with saline or 0.1, 1, or 5 micrograms/100 g BW of thyroxine for 22 days. Thyroxine injections decreased body weight gain but did not affect bone length and width. The epiphyseal growth plate was thinner and the activities of bone alkaline and acid phosphatase in energy deficient and 5 micrograms/100 g BW thyroxine injected animals were lower than that of the other treatment groups. Serum total thyroxine and triiodothyronine concentrations were increased but somatomedin C concentration was decreased by injecting with 5 micrograms/100 g BW of thyroxine in energy deficient rats.