Thermoregulatory responses in exercising rats: methodological aspects and relevance to human physiology

Abstract

Rats are used worldwide in experiments that aim to investigate the physiological responses induced by a physical exercise session. Changes in body temperature regulation, which may affect both the performance and the health of exercising rats, are evident among these physiological responses. Despite the universal use of rats in biomedical research involving exercise, investigators often overlook important methodological issues that hamper the accurate measurement of clear thermoregulatory responses. Moreover, much debate exists regarding whether the outcome of rat experiments can be extrapolated to human physiology, including thermal physiology. Herein, we described the impact of different exercise intensities, durations and protocols and environmental conditions on running-induced thermoregulatory changes. We focused on treadmill running because this type of exercise allows for precise control of the exercise intensity and the measurement of autonomic thermoeffectors associated with heat production and loss. Some methodological issues regarding rat experiments, such as the sites for body temperature measurements and the time of day at which experiments are performed, were also discussed. In addition, we analyzed the influence of a high body surface area-to-mass ratio and limited evaporative cooling on the exercise-induced thermoregulatory responses of running rats and then compared these responses in rats to those observed in humans. Collectively, the data presented in this review represent a reference source for investigators interested in studying exercise thermoregulation in rats. In addition, the present data indicate that the thermoregulatory responses of exercising rats can be extrapolated, with some important limitations, to human thermal physiology.

Leptin, adiponectin, and ghrelin responses to endurance exercise in different ambient conditions

“…Specifically, high body surface area-to-mass ratio and differences in metabolism and thermal tolerance of rats may explain changes in hormone responses compared with those observed in humans. 44,45 Lack of differences in hormone concentrations between temperatures in the current study may be due to the relatively short exposure times incorporated into the current design. In non-human models exposures were 8 to 24 times longer 37,38 and more intense, [37][38][39]43 than in the current study.…”

Pre-exercise exposure to the treadmill setup changes the cardiovascular and thermoregulatory responses induced by subsequent treadmill running in rats

“…Laboratory rodents, including rats, are commonly used to investigate the mechanisms underlying physical exercise-induced physiological responses, such as cardiovascular and thermoregulatory responses, [1][2][3][4][5][6] particularly in experiments involving invasive procedures. 7 Such studies provide important contributions to our understanding of the central mechanisms involved in the regulation of core body temperature (T CORE ) [8][9][10] and mean arterial pressure (MAP) 11,12 during physical exercise.…”

“…Treadmill running is frequently used by researchers because it allows exercise intensity to be precisely controlled and T CORE , tailskin temperature (T SKIN ) and MAP to be continuously measured while the rat is running. 6 Different methodological approaches have been used to conduct experiments aimed at evaluating thermoregulatory and cardiovascular responses during treadmill running. Some experimenters expose rats to the treadmill setup before initiating exercise (i.e., rats are placed on the treadmill belt until their T CORE and/ or MAP stabilize) 10,[13][14][15] to minimize the influence of handling and being placed into an anxiety-inducing environment on physiological responses to subsequent running.…”

“…A recent study reported that, in some cases, the T CORE of rats did not return to baseline values even after 2-3 h of treadmill exposure. 6 Using this protocol, experimenters have frequently observed initial T CORE values (measured in the abdomen) above 37.5 C. 10,[13][14][15] In contrast, when exercise is initiated immediately after transfer from the home cage to the treadmill, which involves animal handling, the rats usually present initial abdominal temperatures near 37.0 C. 8,17,18 These studies show that the T CORE of rats at the beginning of exercise is higher under experimental protocols in which the rats are exposed to the treadmill prior to exercise than in protocols in which they are not previously exposed to the treadmill. This difference in initial T CORE may affect thermoregulatory responses during exercise and ultimately affect aerobic performance.…”

Brazil: What country is this?

“…The Brazilian diversity can also be noticed when looking at the topics of the manuscripts published in this special issue, with papers focusing on behavioral thermoregulation, 19 brown adipose tissue thermogenesis, 20 circadian rhythms of body temperature, 21 heat acclimation, 22 exercise thermoregulation, 23 mediators of thermoregulatory manifestations induced by systemic inflammation, 24,25 motion sickness-induced hypothermia, 26 and temperature and Alzheimer disease 27 …”