[Hypothalamo-pituitary axis: effects of physical training in rats administered with dexamethasone]

To investigate the effects of physical training associated to dexamethasone administration in carbohydrate metabolism and adrenocorticotrophic hormone (ACTH) release.

Young Wistar rats were divided into four groups: sedentary control (CS), sedentary dexamethasone (DxS), trained control (CT) and trained dexamethasone (DxT). The rats were submitted to swimming training associate to administration of dexamethasone for ten weekends. Before sacrifice the rats received subcutaneous insulin to calculate the maximum decreased in blood glucose. Venous blood was sampled obtained at the end experiment period to determine glucose, insulin, free fatty acids (FFA) and ACTH. Gastrocnemius and liver tissue samples were used to determination glycogen, and adipose epididymal tissue was used to measured the weight.

Dexamethasone administration provoke insulin resistance and the physical training reverted this aspect. Training promoted increase in muscle and liver glycogen store and a high utilization of FFA. Moreover, the dexamethasone provoke decreased of ACTH release in response to acute exercise, showing marked differences in the functioning of the hypothalamy-pituitary-adrenal (HPA) axis between groups of rats.

a) Low-dose of dexamethasone promote several side effects in metabolism intermediary and chronic exposure to steroid was associated with insulin resistance; b) The regular swimming exercise promoted increased insulin sensitivity. Therefore, exercise can override the dexamethasone negative feedback of the HPA axis activation in rats.