Treadmill running produces both positive and negative physiological adaptations in Sprague-Dawley rats

Abstract

Exercise training produces a vast array of physiological adaptations, ranging from changes in metabolism to muscle mitochondrial biogenesis. Researchers studying the physiological effects of exercise often use animal models that employ forced exercise regimens that include aversive motivation, which could activate the stress response. This study examined the effect of forced treadmill running (8 wk) on several physiological systems that are sensitive to training and stress. Forced treadmill running produced both positive and negative physiological adaptations. Indicative of positive training adaptations, exercised male Sprague-Dawley rats had a decrease in body weight gain and an increase in muscle citrate synthase activity compared with sedentary controls. In contrast, treadmill running also resulted in the potentially negative adaptations of adrenal hypertrophy, thymic involution, decreased serum corticosteroid binding globulin, elevated lymphocyte nitrite concentrations, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM. Such alterations in neuroendocrine tissues and immune responses are commonly associated with chronic stress. Thus treadmill running produces both positive training adaptations and potentially negative adaptations that are indicative of chronic stress. Researchers employing forced activity need to be aware that this type of exercise procedure also produces physiological adaptations indicative of chronic stress and that these changes could potentially impact other measures of interest.

Voluntary wheel running initially increases adrenal sensitivity to adrenocorticotrophic hormone, which is attenuated with long-term training

“…Indeed, ACTH upregulates the expression of its own receptors on adrenocortical cells in such a feed-forward manner (21,28). In accordance with this, 2 wk of voluntary wheel running have recently been shown to increase mRNA levels of StAR (25). Alternatively, a recent study has also suggested that enhanced sympathoadrenomedullary activity, found to be associated with exercise training, may positively modulate adrenal sensitivity to ACTH (8).…”

“…In rodents, the effect of exercise on diurnal HPA activity and adrenal sensitivity to ACTH is also unclear. For example, compared with S animals, trained animals have increased resting stress hormones (17,25), while others show similar resting concentrations (14,27) or even decreased resting concentrations (4,7,9,19). It is likely that the variety of training protocols and the varying training durations used, as well as the timing of blood sampling in these rodent studies, contributes to the discrepancies in findings.…”

“…The effects of regular exercise on diurnal GC levels and adrenal sensitivity to ACTH secretion are unclear. Previously, a number of rodent studies investigating the effects of training on the HPA axis have employed forced exercise paradigms for their method of training (1,25,27,36). Such studies have produced findings that are similar to those of investigations employing chronic stress (e.g., repeated restraint stress) as an activator of the axis (17,32), making it difficult to delineate the effects of perceived stress from the exercise itself.…”

Chronic voluntary wheel running facilitates corticosterone response habituation to repeated audiogenic stress exposure in male rats

“…It has been argued that exercise training in and of itself is stressful and therefore caution is advised when interpreting behavioral or endocrine response adaptations (or the lack thereof) to subsequent challenges or stressors, as they could be masked or altered by the chronic stress inherent in the training (Moraska et al 2000;Burghardt et al 2004). Indeed, certain forced exercise training paradigms in controlled animal studies have resulted in physiological adaptations, including adrenal hypertrophy and/or thymic involution, that are typically associated with chronic activation of the HPA-axis system (Selye 1936).…”

Effects of physical exercise and social isolation on anxiety-related behaviors in two inbred rat strains

“…Although the meaning of this behavior is complex, peripheral locomotion is often interpreted as locomotor activity (Ramos et al, 2003;Izídio et al, 2011). Thus, it can be suggested that the PE-induced increase in cardiovascular or muscular capacity of these animals (Moraska et al, 2000) facilitated locomotion in the OF. Alternatively, the increase in general locomotion may be a result of the selection of animals that completed the treadmill training, i.e., rats with baseline increased locomotion.…”