The effects of graded levels of calorie restriction: III. Impact of short term calorie and protein restriction on mean daily body temperature and torpor use in the C57BL/6 mouse

Abstract

A commonly observed response in mammals to calorie restriction (CR) is reduced body temperature (Tb). We explored how the Tb of male C57BL/6 mice responded to graded CR (10 to 40%), compared to the response to equivalent levels of protein restriction (PR) over 3 months. Under CR there was a dynamic change in daily Tb over the first 30–35 days, which stabilized thereafter until day 70 after which a further decline was noted. The time to reach stability was dependent on restriction level. Body mass negatively correlated with Tb under ad libitum feeding and positively correlated under CR. The average Tb over the last 20 days was significantly related to the levels of body fat, structural tissue, leptin and insulin-like growth factor-1. Some mice, particularly those under higher levels of CR, showed periods of daily torpor later in the restriction period. None of the changes in Tb under CR were recapitulated by equivalent levels of PR. We conclude that changes in Tb under CR are a response only to the shortfall in calorie intake. The linear relationship between average Tb and the level of restriction supports the idea that Tb changes are an integral aspect of the lifespan effect.

Effects of Sex, Strain, and Energy Intake on Hallmarks of Aging in Mice

“…One of the primary physiological responses to CR is the reduction in body temperature (Weindruch et al, 1979) in both rodents (Duffy et al, 1989; Mitchell et al, 2015a; Speakman and Mitchell, 2011), non-human primates (Lane et al, 1995) and humans (Soare et al, 2011). We measured rectal body temperature ( T b ) during the dark cycle and found that D2 mice had generally lower T b compared to B6 mice, with a trend toward T b reduction with CR versus AL (Figure 1D).…”

“…The reduction in body temperature ( T b ) has been postulated to play a role in the CR-promoting effects on lifespan in rodents and non-human primates (Duffy et al, 1989; Lane et al, 1995; Mitchell et al, 2015a; Speakman and Mitchell, 2011; Turturro and Hart, 1991). Interestingly, strains of mice that maintain high T b are more likely to have extended lifespan under CR (Speakman and Mitchell, 2011).…”

Calorie restriction in rodents: Caveats to consider

“…We know now that this level of CR may be excessive for some strains of mice. The interaction between the degree of CR and different aspects of physiology has been recently examined (Derous et al, 2016a; Derous et al, 2016b; Lusseau et al, 2015; Mitchell et al, 2015a; Mitchell et al, 2016a; Mitchell et al, 2015b; Mitchell et al, 2015c) and survival (Mitchell et al, 2016b). …”

“…Efforts are now invested to further investigated this interplay between mouse strains, the level of restriction, and their impact on survival. The DBA results of Mitchell et al (2016) and those from John Speakman’s group in which the effects of different grades of CR in B6 mice elicit differential responses (Derous et al, 2016a; Derous et al, 2016b; Lusseau et al, 2015; Mitchell et al, 2015a; Mitchell et al, 2016a; Mitchell et al, 2015b; Mitchell et al, 2015c) open the door for new studies aimed at identify the underlying biological responses. Thus, one could predict that some of the recombinant inbred strains will have a beneficial response to CR if they were tested at a lower level of dietary restriction.…”

The effects of graded levels of calorie restriction: VIII. Impact of short term calorie and protein restriction on basal metabolic rate in the C57BL/6 mouse

“…In some cases these responses have been compared to the equivalent responses to levels of protein restriction (PR) [14, 31, 35, 41]. Here we focus on BMR utilizing an essentially similar approach to that adopted by Selman et al (2005) [40].…”