Influence of light regimens on circadian changes in the blood glucose and tissue glycogen concentration in the rat.

Adult male Wistar rats allowed food and drinking water ad libitum were kept 2- 5 weeks under standard conditions, but with a different artificial light regimens. The standard regimen was 12:12 h light and dark (LD) and the other variants were 12:12 h dark and light (DL), continuous darkness (DD) and continuous light (LL). The blood glucose level and the liver, skeletal muscle, heart and brown and white adipose tissue glycogen concentration were tested during the day at 3-hour intervals. The experiments were carried out during the winter and were evaluated by an analysis of variance and the cosinor test. Circadian variation of the blood glucose level and the liver and both the adipose tissue glycogen concentrations was only slightly affected by changes in the light regimen. Conversely, the oscillations of the skeletal muscle and heart glycogen concentration reacted markedly to the variants of the light regimen, their reaction being manifested in the localization of the acrophases in different parts of the day, especially when comparing the DD and LD regimens.