Enhancement of Calorigenic Response to Cold and to Norepinephrine in Physically Trained Rats

Abstract

Calorigenic response to cold and to norepinephrine (NE : 4μg •kg-1•min-1) in physically fit (SW) rats was compared with control (CT) and cold-acclimated (CA) rats. Physical fitness was obtained by daily 3-hr swimming in water at 36°C for 6-8 weeks. Resting heart rate (HR) was significantly less in SW rats. Cold immersion (in water at 18°C up to the neck) increased oxygen consumption (VO2) significantly in CA and SW compared to CT rats (p<0.01). Cold immersion decreased colonic temperature (Teo1) in all groups. Despite the increased calorigenic response, SW rats cooled as quickly as CT rats in cold water. Body weight and skinfold thickness were significantly less in SW than in CT rats (p<0.01). Compared with CT rats, average weight of the interscapular BAT was significantly less in SW rats (p<0.05). Infusion of NE significantly increased VO2, Teo1, HR and mean aortic pressure in anesthetized rats. The increase in VO2 was significantly greater in CA (p<0.01) and SW (p<0.05) than in CT rats. Teo1 increased significantly in CA (p< 0.05) and slightly in SW compared to CT animals. © 1981, PHYSIOLOGICAL SOCIETY OF JAPAN. All rights reserved.