CIRCADIAN-RHYTHM OF GLYCOGEN IN THE HAMSTER DIAPHRAGM

The purpose of this study was to determine the diurnal fluctuation of glycogen stores for the whole hemidiaphragm and within a specific myof ibrillar ATPase (M-ATPase) fibre type and diaphragmatic region. Fifty- six golden Syrian hamsters were randomly divided into six groups accor ding to the time of sampling biopsies from the diaphragm: 03:00, 07:00 , 11:00, 15:00, 19:00, and 23:00. The right hemidiaphragm was quick fr ozen and biochemically assayed for glycogen levels. Biopsies from the left hemidiaphragm of the same animal were cut from the anterior costa l and crural regions, and stained with periodic acid - Schiff(PAS) and for M-ATPase. Optical density measures of PAS-stained fibres were det ermined to quantitate glycogen in different M-ATPase fibre types and d iaphragmatic regions. Biochemical assay of the entire hemidiaphragm sh owed slightly greater glycogen content of biopsies taken at 11:00 and 15:00 than at 03:00, 19:00, and 23:00 (range of differences: 6.4-10.0% ). However, glycogen levels within a specific M-ATPase fibre type and diaphragm region were not different in biopsies sampled at different t imes. Because the hamster has a small diurnal variation of glycogen in the diaphragm, which is similar to the small diurnal variation of gly cogen in human skeletal muscle, this species may be a good animal mode l for metabolic studies of the diaphragm that could be affected by diu rnal glycogen variability.