Single-housing conditions result in higher running distance than per capita running distance in pair-housing conditions, without affecting cortisol and inflammatory indices in female rats

Objective: Voluntary exercise is frequently used in experimental exercise studies, but it is not known whether isolating animals in this method affects stress. The aim of this study was to compare voluntary physical activity and stress-related factors between single and pair-housed female rats. Materials and Methods: Rats were divided into control single (C-S) and control double (C-D), physically active-single (PAS), and physically active-double (PA-D) groups, and voluntary physical activity was recorded for eight weeks. Cortisol in serum, interleukin 1β (IL-1β), and tumor necrosis factor α (TNFα) in serum and left ventricle were determined to evaluate the stress. Cardiomyocyte morphology was assessed to understand activity-induced cardiac hypertrophy. Results: The mean weekly voluntary activities of the PA-S group were higher than those of the PA-D group from week 3 to week 8 (p<0.05 for all). Cortisol, IL-1β, and TNFα levels were similar in the PA-S and PA-D groups (p>0.05). Cardiomyocyte diameters were similar in the PA-S and PA-D groups (p>0.05), and the data of both groups were higher than the control group (P<0.001 for all). Conclusion: Female rats subjected to voluntary physical activity under single-housing conditions may exhibit higher activity levels than pair-housing rats, but single-housing and pair-housing conditions were similarly effective in terms of stress and exercise-induced cardiac hypertrophy.