Effect of hypothalamic administration of 17-β estradiol on body temperature during cold exposure in the ovariectomized rats

 

Yuki Uchida, Madoka Tohi, Ken Tokizawa, and Kei Nagashima

Laboratory of Integrative Physiology, Faculty of Human Sciences, Waseda University, Tokorozawa, Saitama, Japan

 

BACKGROUND We reported that ovariectomized rats could not maintain body temperature (T_core) well in the cold; however, local administration of 17-β estradiol (E₂) in the medial preoptic area (MPO) restored the cold tolerance.  The E₂ had no effect on UCP1 mRNA level in the interscapular brown adipose tissues, suggesting less influence on metabolic heat production. AIM To test the hypothesis that the local E₂ administration in the MPO affects heat dissipation, the tail surface temperature was assessed.  METHODS After ovariectomy for 9-wk old rats, a stainless steel pipe was placed in the MPO for local administration of E₂ or cholesterol. A rat was placed at 10 or 25°C for 2h, 48 h after the administration E₂ or cholesterol. T_core and tail temperature (T_tail) were measured by telemetry and thermography.  RESULTS Both the groups showed decrease in T_tail at 10°C; however the reduction was greater in the estrogen group than in the cholesterol group. CONCLUSION Without estrogen in the MPO, heat dissipation from the tail in ovariectomized rats may not be fully suppressed in the cold, resulting in reduction of T_core.

 

Key words: female hormone, tail temperature, medial preoptic area