Energetic response to repeated restraint stress in rapidly growing mice

There is a cost of stress that may result in the loss of normal biological function (e.g., growth). Repeated, and even single, applications of stressors have been shown to induce negative energy balance in rodents. However, here we addressed whether this energetic response changes during multiple stress exposure and whether there is complete recovery subsequent to the cessation of stress exposure. These questions were addressed in growing C57Bl/6 mice (31 day) by determining at different times the energetic and endocrine responses after the exposure to restraint (R) stress for 4 h applied once (R1), repeatedly over 3 days (R3), or repeatedly over 7 days (R7). Compared with control values, R elevated (P< 0.05) plasma corticosterone and reduced plasma insulinlike growth factor I on all days of exposure to the stressor. Seven days, but not 1 or 3 days of R, decreased the net growth (126%, P< 0.05) and deposition of fat (71%, P< 0.05) and lean (60%, P< 0.05) energy over the 7 days. Only R7 depressed the 7-day metabolizable energy intake (P< 0.05), and R7, but not R1 or R3, increased the overall energy expenditure (10%, P< 0.05). Our results demonstrate that repeated episodes of stress are energetically costly to the rapidly growing animal, but compensatory mechanisms mitigate this cost of repeated stress exposure and permit complete recovery of energy balance after the cessation of stress application.