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1 Internal Medicine, Research Centre for Endocrinology and Metabolism (RCEM), Gothenburg, Sweden; Internal Medicine, Wallenberg Laboratory, Sahlgrenska University Hospital, Gothenburg, Sweden
2 Department of Clinical Physiology, Goteborg University, Gothenburg, Sweden; AstraZeneca, Molndal, Sweden
3 Department of Clinical Physiology, Goteborg University, Gothenburg, Sweden
* To whom correspondence should be addressed. E-mail: ingrid.wernstedt{at}medic.gu.se.
Interleukin-6 (IL-6) deficient (-/-) mice develop mature onset obesity. Pharmacological studies have shown that IL-6 has direct lipolytic effects and when administered centrally increases sympathetic outflow. However, the metabolic functions of endogenous IL-6 are not fully elucidated. We aimed to investigate the effect of IL-6 deficiency with respect to cold exposure and cage-switch stress, i.e. situations that normally increase sympathetic outflow. Energy metabolism, core temperature, heart rate and activity were investigated in young pre-obese IL-6 -/- mice by indirect calorimetry together with telemetry. Baseline measurements and the effect of cage-switch stress were investigated at thermoneutrality (30 °C) and at room temperature (20 °C). The effect of cold exposure was investigated at 4 °C. At 30 °C, the basal core temperature was 0.6 ± 0.24 °C lower in IL-6 -/- compared to wild type mice, while the oxygen consumption did not differ significantly. The respiratory exchange ratio at 20 °C was significantly higher and the calculated fat utilization rate was lower in IL-6 -/- mice. In response to cage-switch stress, the increase in oxygen consumption at both 30 and 20 °C was lower in IL-6 -/- than in wild type mice. The increase in heart rate was lower in IL-6 -/- mice at 30 °C. At 4 °C, both the oxygen consumption and core temperature were lower in IL-6 -/- compared to wild type mice, suggesting a lower cold induced thermogenesis in IL-6 -/- mice. The present results indicate that endogenous IL-6 is of importance for stress- and cold-induced energy expenditure in mice.
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