The mechanisms of thermogenesis and thermoregulation were studied in the tr
ee shrew (Tupaia belangeri) and greater vole (Eothenomys miletus) of the su
btropical region, and Brandt's vole (Microtus brandti), Mongolian gerbil (M
eriones unguiculatus), Daurian ground squirrel (Spermophilus dauricus) and
plateau pika (Ochotona curzoniae) of the northern temperate zone. Resting m
etabolic rate (RMR) and non-shivering thermogenesis (NST) increased signifi
cantly in T. belangeri, E miletus, M. brandti and M. unguiculatus after col
d acclimation (4 degreesC) for 4 weeks. In T. belangeri, the increase in RM
R and thermogenesis at liver cellular level were responsible for enhancing
the capacity of enduring cold stress, and homeothermia was simultaneously e
xtended. Stable body temperature in M. brandti, E. miletus, M. unguiculatus
and O. curzoniae was maintained mainly through increase in NST, brown adip
ose tissue (BAT) mass and its mitochondrial protein content? and the upregu
lation of uncoupling protein (UCP1) mRNA, as well as enhancement of the act
ivity of cytochrome C oxidase, ol-glycerophosphate oxidase and T, 5 ' -deio
denase in BAT mitochondria. The RMR in O. curzoniae and euthermic S. dauric
us was not changed, while NST significantly increased during cold exposure;
the former maintained their stable body temperature and mass, while body t
emperature in the latter declined by 4.8 degreesC. The serum T-3 concentrat
ion or ratio of T-3/T-4 in all the species was enhanced after cold acclimat
ion. Results indicated that: (1) the adaptive mechanisms of T. belangeri re
siding in the subtropical region to cold are primarily by increasing RMR an
d secondly by increasing NST, and the mechanisms of thermogenesis are simil
ar to those in tropical mammals; (2) in small mammals residing in northern
regions, the adaptation to cold is chiefly to increase NST: (3) the mechani
sm of cold-induced thermogenesis in E. miletus residing in subtropical and
high mountain regions is similar to that in the north; (4) a low RMR in war
m environments and peak RMR and NST in cold environments enabled M unguicul
atus to tolerate a semi-desert climate; (5) O. curzoniae has unusually high
RMR and high NST, acting mainly via increasing NST to adapt to extreme col
d of the Qinghai-Tibet Plateau; (6) the adaptation of euthermic S. dauricus
to cold is due to an increase in NST and a relaxed homeothermia; and lastl
y (7) the thyroid hormone is involved in the regulation of cold adaptive th
ermogenesis in all the species studied. (C) 2001 Elsevier Science Inc. All
rights reserved.