Single and combined effects of acute and chronic non-thermal stressors on rat interscapular brown adipose tissue metabolic activity

Abstract

The aim of this study was to examine whether the thermogenic potential of rat interscapular brown adipose tissue (IBAT) changes in response to acute and/or chronic exposure to non-thermal stressors (immobilization and isolation), by measuring the uncoupling protein 1 (UCP-1) content, MAO-A, SOD and CAT activities, as well as the number of IBAT sympathetic noradrenaline-containing nerve fibers. Both acute immobilization (2 h) and chronic isolation (21 days), as well as their combined effects, significantly increased the IBAT UCP-1 content in comparison to non-stressed animals. When applied individually, stressors increased the number of sympathetic fibers in comparison to controls, whereas in combination they decreased it. The activity of IBAT monoamine oxidase-A (MAO-A) decreased under the influence of each stressor independent of its type or duration. SOD activity coincided with MAO-A decrement, whereas CAT activity had an opposite pattern of changes. We conclude that acute and chronic exposure to non-thermal stressors, immobilization and isolation, respectively, affect the metabolic potential of rat IBAT, judging by the increase in UCP-1 content and sympathetic outflow. However, when acute immobilization was applied as a novel stressor to previously chronically isolated animals, an increase in the UCP-1 content was accompanied by a lower IBAT sympathetic outflow, suggesting that IBAT metabolic function under various stress condition is not solely dependent on SNS activity.