Calorie restricted rats do not increase metabolic rate post-LPS, but do seek out warmer ambient temperatures to behaviourally induce a fever Academic Article uri icon

abstract

  • Due to previous work where we have demonstrated attenuated febrile responses post-lipopolysaccharide (LPS) in calorie restricted (CR) rodents we aimed to explore metabolic rate and behavioral thermoregulation in these CR animals post-LPS. Male Sprague-Dawley rats fed ad libitum (AL) or restricted to 50% (CR50%) of the AL animals' food intake for 28 days were injected on the 29th day with 50 μg/kg of LPS. Core body temperature (T(b)), self-selected self-selected ambient temperature (T(a)), indirect calorimetry [to determine energy expenditure (EE) and respiratory quotient (RQ)] were measured in AL and CR animals for 8 hours post-LPS. The CR rats chose to sit at a higher T(a) (28.1±0.4°C) compared to the AL rats (23.7±1.4°C) at baseline and the AL rats chose to sit at a warmer T(a) from 30 min until 420 min post-LPS; however, the CR rats selected a warmer T(a) only at 270 min post-LPS. AL rats demonstrated a higher T(b) compared to baseline at 120, 150, and from 240 until 480 min post-LPS. In contrast to our previous findings the CR rats also demonstrated a higher T(b) compared to baseline for most of the time between 270 and 420 min post-LPS. When allowed to select a warmer T(a) the CR rats do so and thereby mount a febrile response, although significantly delayed and shorter-lived. In the indirect calorimetry experiment the AL rats demonstrated an elevated T(b) from 150 until 480 min post-LPS; however, the CR rats fever profile was attenuated, with the only increase occurring at 270 min post-LPS. Indirect calorimetry indicated that the CR rats demonstrated significantly reduced EE (-17.9%±1.3) compared to the AL rats at baseline. After LPS, the AL rats demonstrated an increase in EE at multiple time points between 90 and 420 min, whereas no change was observed in the CR rats. The AL and CR rats demonstrated similar profiles of RQ at baseline and after LPS the AL rats demonstrated a decrease in their RQ at 360, 450, and 480 min, whereas the CR rats demonstrated no difference. The metabolic cost for rats to mount a fever during a period of low food availability may outweigh the benefits of producing a febrile response to a relatively small dose of LPS.

authors

publication date

  • December 2012