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Mejia-Hernandez, Kevyn.
The combined effects of chronic glucocorticoids and exercise training in peripheral tissues of male Sprague Dawley rats.
M. Sc. -- York University, 2009
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2010]
2 microfiches
Includes bibliographical references.
Although acute elevations in glucocorticoids (GC) are beneficial, prolonged exposure causes detrimental effects including muscle wasting and increased fat. We developed an animal model with an abolished diurnal GC rhythm by elevating basal (AM) levels of GC. We assessed the effects of elevated GC and regular volitional exercise on anthropometric measurements and markers of energy metabolism. Male sprague dawley rats were divided into exercise and sedentary groups and further divided into SHAM controls and corticosterone (CORT) groups. Exercisers had 24-h access to running wheels for 6 weeks while sedentary groups remained in standard rodent cages. All subgroups had free access to food and water. CORT rats received two 150mg corticosterone pellets implanted subcutaneously while SHAM rats received wax pellets. Nadir corticosterone (07 00-08 00 h) was at least 2-fold higher in CORT groups than SHAMs eliminating the diurnal pattern. Relative to body weight, CORT groups had ~30% more epididymal fat compared with SHAM groups. The visceral fat deposition in sedentary groups was ~50% greater than exercised groups (main effect of exercise, P<0.05). Expression of hornione sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) in epididymal fat was elevated in exercised groups (main effect of exercise, p<=0.05) depicting a protective mechanism for reducing visceral adiposity. Bone strength was decreased in CORT treated groups (main effect of CORT, p<=0.05) while the mixed gastrocnemius muscle of CORT groups, had a 70% increase in glucocorticoid receptor a/b isoforms (GRa/b) (main effect of CORT p<=0.05) and an increase of 40% in 11 beta-hydroxysteroid dehydrogenase 1 (11[beta]HSD1) (main effect of CORT p<=0.05) content. This study proposes a new animal model of chronic GC overexposure (similar to chronic stress or glucocorticoid therapy) and reveals that anthropometric measures are negatively affected by chronically high basal GC levels. Changes occur in the face of chronic GC treatment by altering GR isoform and 11[beta]HSD1 content in muscle; findings which mimic observations in metabolic syndrome patients. We show that regular exercise attenuates visceral fat mass gain associated with chronically elevated basal GC exposure. These findings suggest a therapeutic role for exercise in conditions associated with chronic elevations in GC.