TAKAHATA Toshinari KANAZAWA INST. TECHNOLOGY, ASSOCIATE PROF., 助教授 (90159004)
NAGASAKA Tetsuo KANAZAWA UNIV., SCH. MED., PROFESSOR, 医学部, 教授 (80023646)
TANABE Minoru KANAZAWA UNIV., SCH. MED., INSTRUCTOR, 医学部, 助手 (20217110)
|Budget Amount *help
¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1992 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1991 : ¥1,100,000 (Direct Cost : ¥1,100,000)
After the rats were exposed to heat loaded for about 5 h during the last half of the dark phase for 10 consecutive days, body temperature of the rats significantly decreased during the period corresponding to that of the previous heat exposure time (Shido et al., 1991). The objective of this project was to clarify the mechanism of characteristic fall in body temperature. The heat-exposed (HE) rats were subjected to 33.0ﾟC for about 5 h in the last half of the dark phase for more than 2 weeks and control (CN) rats were kept at 24ﾟC. After the completion of the schedule, the levels of hypothalamic temperature (Thy), heat loss, heat production, feeding activity (FA) and body movement were significantly lower in the HE than in the CN during the period when the HE rats had been exposed to heat. Even in fasting condition from 6 h before the start of the experiment, significant difference in Thy still existed. These results suggest that the characteristic fall in Thy is partly mediated by the decrease in FA, however, there are also another contributors. To investigate the contribution of plasma levels of thyroid hormones and energy substrates, plasma levels of triiodothyronine (T3), free T3 (FT3), thyroxin (T4), free T4 (FT4), triglyceride, non esterified fatty acid, total protein and glucose were measured at 3 h interval between 0000 and 1800 h (dark phase, 0300-1500 h). Plasma levels of T3 and FT3 during the previous heat exposure period were significantly higher in the HE than in the CN. Similar differences were observed in T4 and FT4 levels. Plasma levels of energy substrates did not differ between 2 groups. These results suggest minimum contributions of thyroid hormones to the characteristic falls in Thy in the HE rats. Farther studies are required to clarify the mechanisms of the characteristic fall in Thy.