Increased thermogenic capacity of brown adipose tissue under low temperature and its contribution to arousal from hibernation in Syrian hamsters.

Brown adipose tissue (BAT) is thought to play a significant physiological role during arousal when body temperature rises from the extremely low body temperature that occurs during hibernation. The dominant pathway of BAT thermogenesis occurs through the ß(3)-adrenergic receptor. In this study, we investigated the role of the ß(3)-adrenergic system in BAT thermogenesis during arousal from hibernation both in vitro and in vivo. Syrian hamsters in the hibernation group contained BAT that was significantly greater in overall mass, total protein, and thermogenic uncoupling protein-1 than BAT from the warm-acclimated group. Although the ability of the ß(3)-agonist CL316,243 to induce BAT thermogenesis at 36°C was no different between the hibernation and warm-acclimated groups, its maximum ratio over the basal value at 12°C in the hibernation group was significantly larger than that in the warm-acclimated group. Forskolin stimulation at 12°C produced equivalent BAT responses in these two groups. In vivo thermogenesis was assessed with the arousal time determined by the time course of BAT temperature or heart rate. Stimulation of BAT by CL316,243 significantly shortened the time of arousal from hibernation compared with that induced by vehicle alone, and it also induced arousal in deep hibernating animals. The ß(3)-antagonist SR59230A inhibited arousal from hibernation either in part or completely. These results suggest that BAT in hibernating animals has potent thermogenic activity with a highly effective ß(3)-receptor mechanism at lower temperatures.

Seasonality and fasting effect in raccoon dog Nyctereutes procyonoides serum leptin levels determined by canine leptin-specific enzyme-linked immunosorbent assay.

Leptin is an adipocyte-derived peptide hormone that acts on the brain and regulates food intake and energy balance. Several previous reports have suggested that overwintering raccoon dogs Nyctereutes procyonoides are able to control their adiposity efficiently, but the contribution of leptin to weight regulation in these animals remains unclear. To study the seasonality of overwintering raccoon dogs as well as the effects of fasting on them, serum leptin levels were investigated using a newly established canine leptin-specific enzyme-linked immunosorbent assay (ELISA) kit. Of the nine animals studied, five were fed and four were fasted (deprived of food for 2 months in winter). Blood samples and body fat weights were monitored once a month throughout the experimental period (July 2007-March 2008). Leptin concentrations obtained by ELISA were significantly higher than and had a positive correlation with those obtained by previously used multispecies radioimmunoassay (RIA) kits. Moreover, ELISA showed a clearer correlation between the body fat weight and leptin levels compared with RIA, suggesting the efficacy of canine leptin-specific ELISA kit for leptin estimation in raccoon dogs. Autumnal fattening was observed in both groups of animals, but the wintertime loss of adipose tissue was more obvious in the fasted group. Serum leptin concentrations determined by ELISA showed seasonal changes without significant differences between the fed and fasted animals. Therefore, high levels of leptin may be responsible for the suppression of feeding behavior in raccoon dogs before winter.

Overwintering strategy of wild free-ranging and enclosure-housed Japanese raccoon dogs (Nyctereutes procyonoides albus).

The raccoon dog, Nyctereutes procyonoides, is a canid with a passive overwintering strategy in northern Europe. However, the behaviour and physiology of the Japanese subspecies, N. p. albus, which has fewer chromosomes than the other subspecies, remain unknown. We measured body temperature, body composition and blood biochemistry of wild free-ranging and fasted enclosure-housed N. p. albus during boreal winter in Hokkaido, Japan. Body temperature of N. p. albus decreased from 38 degrees C in autumn to 35.9-36.7 degrees C while maintaining a circadian rhythm in late February (n = 3). A transient 18-36% decrease in resting heart rate occurred when body temperature was low (n = 2). Despite a 33-45% decrease in body weight due to winter fasting, circulating glucose, total protein and triglyceride levels were maintained (n = 4). Serum urea nitrogen dropped by 43-45% from autumn to spring, suggesting protein conservation during fasting. The overwintering survival strategy of N. p. albus in central Hokkaido is based upon large changes in seasonal activity patterns, winter denning and communal housing without the large decrease in body temperature that is characteristic of subarctic animals exhibiting hibernation or torpor.

Molecular cloning and tissue distribution of uncoupling protein 1 (UCP1) in plateau pika (Ochotona dauurica).

Uncoupling protein 1 (UCP1) is present exclusively in brown adipose tissue, and contributes to body temperature control during cold exposure. We cloned UCP1 cDNA of plateau pika (Ochotona dauurica), a small, non-hibernating, diurnal lagomorph that inhabits in relatively cold climates and at high altitudes in Mongolia and in northern China. The nucleotide sequence of pika UCP1 was highly homologous to UCP1 of other species, and the deduced amino acid sequence had some common domains for UCP, including six mitochondrial carrier protein motifs and a putative purine-nucleotide binding site. RT-PCR and Western blot analyses revealed that both UCP1 mRNA and protein were expressed exclusively in the interscapular adipose tissue. These results suggest that pika UCP1 contributes to heat production in brown adipose tissue, as do those in other species.

Brown fat UCP1 is not involved in the febrile and thermogenic responses to IL-1beta in mice.

The activity of brown adipose tissue (BAT), a site of nonshivering metabolic thermogenesis, has been reported to increase after interleukin (IL)-1beta/lipopolysaccharide injection. To clarify the possible contribution of BAT thermogenesis to whole body febrile response, we investigated febrile and thermogenic response to IL-1beta using mice deficient in uncoupling protein-1 (UCP1), a key molecule for BAT thermogenesis. In wild-type (WT) mice, IL-1beta injection (5 microg/kg ip) increased body temperature (+1.82 degrees C at 20 min), decreased physical activity (-37% at 1 h), and produced a slight and insignificant rise (+15% at 1 h) in oxygen consumption (Vo(2)). Vo(2) dependent on metabolic thermogenesis (DeltaVO2 thermogenesis) calculated by correcting the effect of physical activity was increased after IL-1beta injection (726 +/- 200 ml x h(-1) x kg(-1) at 1 h). Almost the same responses were observed in UCP1-deficient mice, showing 638 +/- 87 ml x h(-1) x kg(-1) of DeltaVO2 thermogenesis at 1 h. In contrast, CL316,243, a selective activator of BAT thermogenesis, increased body temperature, decreased physical activity, and produced a significant rise in Vo2 in WT mice, showing 1,229 +/- 35 ml x h(-1) x kg(-1) of DeltaVO2 thermogenesis at 1 h. These changes were not observed in UCP1-deficient mice. These results, conflicting with a previously proposed idea of a role of BAT in fever, suggest a minor contribution of BAT thermogenesis to IL-1beta-induced fever. In support of this, we found no effect of IL-1beta on triglyceride content and UCP1 mRNA level in BAT, in contrast with apparent effects of CL316,243.

Day-night difference in ß3-adrenoceptor agonist-induced energy expenditure: Contribution of brown fat thermogenesis and physical activity.

SUMMARY: ß3-adrenergic receptor (ß3-AR) agonist, a drug that reduces body fat, stimulates lipomobilization from white adipose tissue (WAT) and thermogenesis in brown adipose tissue (BAT). To test the day-night difference in the effects of ß3-AR agonist, in the present study, we examined the responses of lipomobilization and energy expenditure to CL316,243 (CL) during the daytime at 10:00 and nighttime at 22:00 in mice kept in a 12 h light-dark cycle with lights on from 07:00. CL injection increased plasma free fatty acid to the same extent at 10:00 and 22:00. In contrast, CL injection increased total oxygen consumption more markedly at 10:00 than 22:00. Physical activity was suppressed by CL injection especially at 22:00. Correcting total oxygen consumption by the suppressive effect on physical activity, oxygen consumption dependent on BAT thermogenesis was estimated. This revealed that the effect of CL on BAT thermogenesis was not different between 10:00 and 22:00. Thus, we concluded that there is no day-night difference in the CL effects on lipomobilization from WAT and thermogenesis in BAT. The stronger effect of CL on total energy expenditure in the daytime was largely due to a more suppressive effect on physical activity in the nighttime.: