暑熱感作(34°)がラットの骨成長と甲状腺ホルモンに与える影響

抄録

The experiment was to investigate the changes of physical traits and enzyme activities in the femur and the change of thyroid hormones in blood serum after heat exposure in growing rats. Wistar strain male rats aged 6 weeks were divided into two groups and placed in temperature controlled rooms; ambient temperature 24° (group C) and 34° (group H). On days 6, 12 and 18 from the beginning of experiment, blood and femur samples were collected from every rat. The blood samples were analyzed thyroid hormone concentrations and the femur samples were measured alkaline and acid phosphatase activities and physical traits. The elongation of the femur was not affected but the growth in width was retarded at high ambient temperature. Bone alkaline phosphatase activity dropped substantially at the beginning of heat exposure and then became stable, while bone acid phosphatase activities were lower in group H than in group C throughout the experimental period. The changes of bone enzyme activities indicate that the retardation of bone growth in width might be related to the reduction of mineralization at the beginning of heat exposure and the following bone resorption. Thyroxine (T₄), riiodothyronine (T₃) and free thyroxine concentrations in blood serum were lower in group H than in group C. The ratio of T₃ to T₄ was not changed by heat exposure.