Effect of short-term immobilization at different times of day on circadian blood glucose and tissue glycogen oscillations in the rat.

Male Wistar rats (body mass 200-250 g) kept under standard vivarium conditions with an artificial illumination regimen (12 h light, 12 h dark) and fed ad libitum were immobilized in boxes 90 min prior to being decapitated at 3-h intervals over a 24-h period. The controls, which were examined at the same times, were deprived of food and water 90 min before being decapitated. The glucose concentration in the animals' blood and the glycogen concentration in their liver, heart, skeletal muscle and white and brown adipose tissue were determined. The experiment was carried out at the end of the autumn; the results were evaluated by an analysis of variance and a cosinor test. The effect of short-term immobilization was manifested in a marked increase in the blood glucose and heart and skeletal muscle glycogen mesor values and in a drop in the liver glycogen mesor value. The main characteristics of circadian oscillations of the liver, heart and white and brown adipose tissue glycogen were the same as in unstressed animals, but marked changes occurred in circadian skeletal muscle glycogen and blood glucose levels. The results indicate that the response of the rat blood glucose and tissue glycogen level to immobilization is differentiated and that the organism's response is correlated to the time of application of the stressor.