Proceedings of The Physiological Society

University of Bristol (2005) J Physiol 567P, PC64

Poster Communications

Hypothalamic-pituitary-adrenocortical axis changes evoked by long-term voluntary exercise in rats

Droste, Susanne Katrin; Chandramohan, Yalini; Reul, Johannes MHM;

1. Henry Wellcome LINE, University of Bristol, Bristol, United Kingdom.

Studies in rats and mice have shown that voluntary exercise has positive effects on various physiological, metabolic and neurobiological processes. There is evidence that voluntary exercise results in an improved coping with stressful challenges of which the underlying neurobiological mechanisms are, however, still unclear. We studied changes in physical parameters and the hypothalamic-pituitary-adrenocortical (HPA) axis in male Sprague Dawley rats (n=12 per group) after giving them access to a running wheel in their home cage for 4 weeks. The rats used the wheel immediately and ran approximately 6 km per night. All animals were humanely killed at the end of the experiment. In general, the exercising rats showed less weight gain (ANOVA with repeated measures: interaction of time and wheel: F(1,22)=8.5, p<0.05; overall effect of wheel: F(1,22)=12.5, p<0.05) and substantially less abdominal fat tissue (2.0 ± 0.1 g) than control rats (2.8 ± 0.1 g; p<0.05, Student's t test). The thymus weight was reduced in the exercising rats (351 ± 21 mg vs. 474 ± 20 mg; p<0.05, Student's t test) and the adrenal weight was unchanged (50.2 ± 1.4 mg vs. 50.2 ± 1.4 mg; n.s., Student's t test). The early morning baseline and forced swimming-induced levels of plasma corticosterone were increased in the exercising rats as compared to the controls (baseline: 29 ± 6.5 ng/ml vs. 13.63 ± 1.8 ng/ml; p<0.05, Student's t test; forced swim: 631.4 ± 89.4 ng/ml vs. 314.3 ± 51.7 ng/ml; p<0.05, Student's t test) whereas ACTH levels were similar (baseline: 76.73 ± 6.79 pg/ml vs. 81.8 ± 6.4 pg/ml; n.s., Student's t test; forced swim: 600.4 ± 49.1 pg/ml vs. 577.2 ± 56.1 pg/ml; p<0.05, Student's t test) measured by radioimmunoassay. Tyrosine hydroxylase (TH) mRNA in the adrenal medulla was measured as an index for the sympathoadrenomedullary activity in these rats. Exercising rats showed higher TH mRNA levels in the right adrenal gland compared to control rats (7715 ± 701 vs. 5581 ± 551 area (square pixel/1000)); two-way ANOVA followed by post-hoc test with contrasts. Furthermore, corticotropin-releasing hormone and arginine-vasopressin mRNA levels were determined in the paraventricular nucleus of snap-frozen brain tissue sections. So far our results indicate that long-term voluntary exercise evokes distinct changes in HPA axis regulation and body composition in rats.

Where applicable, experiments conform with Society ethical requirements