Adaptive changes in the thermogenesis of rats by cold acclimation and deacclimation

Adaptive characters of energy metabolism, thermogenesis and body mass in Eothenomys miletus during cold exposure and rewarming

Environmental cues play important roles in the regulation of an animal’s physiology and behavior. The purpose of the present study was to test the hypothesis that ambient temperature was a cue to induce adjustments in body mass, energy intake and thermogenic capacity, associated with changes in serum leptin levels inEothenomys miletus. We found thatE. miletusincreased resting metabolic rate (RMR) and energy intake and decreased body mass when exposed to cold while it showed a significant increase in body mass after rewarming. The increase in body mass after rewarming was associated with the higher energy intake compared with the control. Uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT) increased in the cold and reversed after rewarming. Serum leptin levels decreased in the cold while increased after rewarming, associated with the opposite changes in energy intake. Further, serum leptin levels were positively correlated with body mass and body fat mass. Together, these data supported our hypothesis that ambient temperature was a cue to induce changes in body mass and metabolism. Serum leptin, as a starvation signal in the cold and satiety signal in rewarming, was involved in the processes of thermogenesis and body mass regulation inE. miletus.

NO modulates the molecular basis of rat interscapular brown adipose tissue thermogenesis

Molecular mechanisms underlying interscapular brown adipose tissue (IBAT) thermogenesis were elucidated. Namely, gene and/or protein expression of uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor gamma (PPARgamma), PPARgamma-coactivator-1alpha (PGC-1alpha), vascular endothelial growth factor (VEGF) and proliferating cell nuclear antigen (PCNA) - key molecules that regulate thermogenesis-related processes - mitochondriogenesis, angiogenesis and IBAT hyperplasia, in rats subjected to cold (4+/-1 degrees C) for 1, 3, 7, 12, 21 and 45days were investigated. Particularly, to examine influence of nitric oxide (NO) on IBAT thermogenic-program, cold-exposed animals were treated by l-arginine or N(omega)-nitro-l-arginine-methyl ester (L-NAME). Related to control (22+/-1 degrees C), cold induced time-coordinated UCP1, PPARgamma and PGC-1alpha transcriptional activation accompanied by PCNA activation and increased VEGF immunolabeling that correlate with endothelial NO synthase (eNOS) transcriptional activation suggesting NO involvement in these thermogenic-factors activation. Observed molecular changes were translated into increased mitochondrial-remodeling, angiogenesis, and IBAT hyperplasia. l-Arginine augmented and prolonged cold-induced increase of eNOS, inducible NOS and thermogenic-molecules expression, IBAT nerve supply, vascularity, hyperplasia and mitochondrial-remodeling, while L-NAME had an opposite effects. Results show that NO improves thermogenesis-related mitochondriogenesis, angiogenesis and tissue hyperplasia, positively affecting molecular basis of these processes, suggesting that NO is an essential regulator of IBAT thermogenic-program operating, at genes, proteins and tissue structure levels.

Physiological and molecular evidence of heat acclimation memory: a lesson from thermal responses and ischemic cross-tolerance in the heart

Sporadic findings in humans suggest that reinduction of heat acclimation (AC) after its loss occurs markedly faster than that during the initial AC session. Animal studies substantiated that the underlying acclimatory processes are molecular. Here we test the hypothesis that faster reinduction of AC (ReAC) implicates "molecular memory." In vivo measurements of colonic temperature profiles during heat stress and ex vivo assessment of cross-tolerance to ischemia-reperfusion or anoxia insults in the heart demonstrated that ReAC only needs 2 days vs. the 30 days required for the initial development of AC. Stress gene profiling in the experimental groups highlighted clusters of transcriptionally activated genes (37%), which included heat shock protein (HSP) genes, antiapoptotic genes, and chromatin remodeling genes. Despite a return of the physiological phenotype to its preacclimation state, after a 1 mo deacclimation (DeAC) period, the gene transcripts did not resume their preacclimation levels, suggesting a dichotomy between genotype and phenotype in this system. Individual detection of hsp70 and hsf1 transcripts agreed with these findings. HSP72, HSF1/P-HSF1, and Bcl-xL protein profiles followed the observed dichotomized genomic response. In contrast, HSP90, an essential cytoprotective component mismatched transcriptional activation upon DeAC. The uniform activation of the similarly responding gene clusters upon De-/ReAC implies that reacclimatory phenotypic plasticity is associated with upstream denominators. During AC, DeAC, and ReAC, the maintenance of elevated/phosphorylated HSF1 protein levels and transcriptionally active chromatin remodeling genes implies that chromatin remodeling plays a pivotal role in the transcriptome profile and in preconditioning to rapid cytoprotective acclimatory memory.

Energy metabolism, thermogenesis and body mass regulation in Brandt's voles (Lasiopodomys brandtii) during cold acclimation and rewarming

Environmental cues play important roles in the regulation of an animal's physiology and behavior. The purpose of the present study was to test the hypothesis that ambient temperature was a cue to induce adjustments in body mass, energy intake and thermogenic capacity, associated with changes in serum leptin levels in Brandt's voles (Lasiopodomys brandtii). We found that Brandt's voles increased resting metabolic rate (RMR) and energy intake and kept body mass stable when exposed to the cold while showed a significant increase in body mass after rewarming. The increase in body mass after rewarming was associated with the higher energy intake compared with control. Uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT) increased in the cold and reversed after rewarming. Serum leptin levels decreased in the cold while increased after rewarming, associated with the opposite changes in energy intake. Further, serum leptin levels were positively correlated with body mass and body fat mass. Together, these data supported our hypothesis that ambient temperature was a cue to induce changes in body mass and metabolism. Serum leptin, as a starvation signal in the cold and satiety signal in rewarming, was involved in the processes of thermogenesis and body mass regulation in Brandt's voles.

Effects of long-term cold exposure on contractile muscles of rats

The effects of 20-week cold exposure on contractile properties of soleus and extensor digitorum longus (EDL) muscles and plasma hormone levels were studied in rats. Twenty male Wistar rats (5 week old) were randomly divided into 2 groups (n = 10 each): cage-control and cold-exposed. The rats in the cold-exposed group were immersed in shoulder-deep water (approximately 18 degrees C) for 1 h/d, 5 d/week, for 20 weeks. The temperature and humidity of the animal room with 12:12 h light-dark cycle were maintained at approximately 23 degrees C and 55%, respectively. The rats were pair-fed powdered diets. The electromyogram activities in soleus and EDL were elevated by cold exposure. The body weight and absolute soleus wet weight of the cold-exposed group were significantly less than controls at the end of experiment. The one-half relaxation time and contraction time of EDL were significantly longer in the cold-exposed group than in the control group. The rate of twitch tension development, normalized by the maximum twitch tension, in EDL of the cold-exposed group was less than in the control group. Further, the fatigue resistance of EDL, but not of soleus, in response to train stimulation at 10 Hz was improved by cold exposure. The plasma levels of thyroid hormones, 3,5,3'-triiodothyronine and thyroxine, were significantly greater in cold-exposed group. Similar changes were also seen in the plasma catecholamine levels in the cold-exposed group (p > 0.05). It is suggested that long-term cold exposure causes a shift of the contractile properties of fast-twitch EDL muscle toward the slow-twitch type. The results also indicated that the characteristics of muscles responded more strongly to an increased activity level than to the elevation of plasma hormones.