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Thermoregulatory, Cardiovascular, and Metabolic Responses to Mild Caloric Restriction in the Brown Norway Rat
Aydin, C. AND C. Gordon. Thermoregulatory, Cardiovascular, and Metabolic Responses to Mild Caloric Restriction in the Brown Norway Rat. Physiological Reports. American Physiological Society, Bethesda, MD, 1(2):e00016, (2013).
Caloric restriction is often used in behavioral toxicological studies where it is necessary to limit food availability such that a test animal will be motivated to perform an operant task. Rats are typically allowed to feed ad libitum but this leads to excessive weight gain. Limiting the amount of food given to a rat, leading to a 10-25% reduction in the ad libitum body weight is a commonly used technique; however, very little is known on the long-term effects of caloric restriction on basic physiological and behavioral processes. The current study addresses the impact of caloric restriction on the cardiovascular and thermoregulatory systems as well as effects on motor activity. The results will lead to a better means of understanding the mechanisms of caloric restriction and shed light into how caloric restriction increases life span.
Caloric restriction (CR) has been demonstrated to prolong the life span of a variety of species. CR-induced reduction in core temperature (Tc) is considered a key mechanism responsible for prolonging life span in rodents; however, little is known on the regulation of CR-induced hypothennia as a function of the circadian cycle. We assessed how mild (10%) CR affected the 24 hour patterns of Tc as well as heart rate (HR) and motor activity (MA) of the Brown Norway rat. Telemetered rats were allowed to feed for 20 weeks ad libitum (AL) or given a CR diet. Tc, HR, and MA of CR rats exhibited nocturnal reductions and diurnal elevations, opposite to that of AL rats. The effects of CR appeared to peak at --4 wk. Metabolic rate (MR) and respiratory quotient (RER) were measured overnight after 6 wk of CR. MR and RER were elevated markedly at the time of feeding in CR rats and then declined during the night. We found that the pattern of Tc was altered with CR, characterized by elimination of high nocturnal Tc’s typically observed in AL animals. In terms of mechanisms to prolong life span in CR animals, we suggest that the shift in pattern of Tc during CR (i.e., elimination of high Tc’s) may be as critical as the overall mean reduction in Tc. Moreover, the timing of feeding will have a marked effect on the thennoregulatory response in calorically restricted rats.