Thermogenesis associated with spontaneous activity: an important component of thermoregulatory needs in rats.

Abstract

1. Quantification of the energy cost of spontaneous activity in freely moving lean and obeseZucker rats was performed at 28°C and during acute cold exposure (from 28 to 5°C).2. An open-circuit metabolic chamber was supplemented with an ultrasensitive ergometric platform equipped with six unidirectional accelerometers and with an opto-electronic device for location of the rat's centre of mass. 3. Resting and mean metabolic rates during control and cold-exposure periods were similar in both groups of rats. The 'extra thermogenesis' (ET), i.e. the difference between mean and resting metabolic rate, amounted to 1 7 + I 1 and 8 6 + 0 7 % of resting metabolic rate at 28 0C, and 39X7 + 2X9 and 34X1 + 2X9% of resting metabolic rate during cold exposure for lean and obese rats, respectively. 4. During the control period obese rats moved 3-71 + 0-61 m h-1 and lean rats 8X69 + 0 57 m h-, but during cold exposure the distance moved by obese rats increased 3X58 + 0X33-fold whereas that moved by lean rats only increased 1-40 + 0*06-fold. The external work performed during spontaneous activity seldom reached 1I0 % of the increase in metabolic rate. 5. In obese rats, weight was a good predictor of the distance covered, and cold exposure induced the same percentage increase in both distance and ET. Activity-associated thermogenesis of obese rats was the predominant thermogenic source that substituted for their atrophied brown fat thermogenesis whereas in lean rats with active brown fat these correlations were not found.

Neuropeptidergic Mediators of Spontaneous Physical Activity and Non-Exercise Activity Thermogenesis

“…Morrison [27] first demonstrated that SPA in rodents accounted for 25% of total energy expenditure, the magnitude of which was later confirmed by Brown et al [28] and Girardier et al [29]. These findings in rodents parallel data from human studies demonstrating the significant impact of SPA-induced energy expenditure on total energy expenditure [9, 16, 30].…”

“…These SPA differences were maintained independent of diet-induced changes in body weight [36]. Likewise, lean rats have greater SPA and SPA-induced energy expenditure compared to obese Zucker rats [29]. Similar relationships between body weight and SPA have been observed in Wistar versus hypoactive Wistar-Kyoto rats [37].…”

Leptin: At the crossroads of energy balance and systemic inflammation

“…This is evident from the fact that young adult (7-10 week-old) Zucker fa/fa rats are capable of mounting vivid thermogenic responses to short-term cold exposure [127][128][129], in spite of their irresponsiveness to leptin. Only at an older age (> 10 week-old) do Zucker fa/fa rats display attenuation of acute thermogenic responses, but such an attenuation coincides with involution of the brown adipose tissue [130].…”

“…The answer to this question is probably negative for two reasons. First, whereas fever is brought about by acute activation of thermoeffectors [103], leptin appears to be unimportant for acute activation of thermogenesis [127][128][129]. Second, the febrile response to LPS is least manifest [133][134][135][136] under the condition (negative energy balance) that is most propitious for activation of thermogenesis by a rise in circulating leptin [56][57][58]60,62].…”

Adaptive thermogenesis and uncoupling proteins: a reappraisal of their roles in fat metabolism and energy balance

“…The efficiency of muscular contraction during exercise is low (~25%), but that of spontaneous physical activity (SPA) (including fidgeting, muscle tone and posture maintenance, and other low-level physical activities of everyday life) is even lower since these essentially involuntary activities comprise a larger proportion of isometric work which is simply thermogenic. Because actual work done on the environment during SPA is very small compared to the total energy spent on such activities, the energy cost associated with SPA has been referred to as movement-associated thermogenesis or SPA-associated thermogenesis [8]. It can also be argued that since SPA is essentially beyond voluntary control, a change in the level or amount of such involuntary SPA in a direction that defends body weight also constitute autoregulatory changes in energy expenditure.…”