BIORHYTHMIC PROFILES IN THE RAT SKELETON

Enzyme activity was studied in different regions of the tibias of ad-lib fed rats sacrificed at intervals of 4 hours throughout a 24 h period. The microchemical profiles revealed that the metabolic activities of the cells in the cartilages and bone have circadian components, but the data implied that the times of most significant linear bone growth and appositional bone growth were not in phase. The cells in the growth apparatus (epiphyseal cartilage and metaphysis) appear to be day-active; they have the highest concentrations of enzymes active in matrix synthesis in the middle of the environmental photofraction, and the greater ability to concentrate radioproline into collagen during the day vs night. By these criteria, the cells in articular cartilage (femur) and diaphyseal bone (tibia) seem metabolically most active during the first 4 hours of darkness. Radiosulfur incorporation (intra-articular injection) into articular cartilage was also sharply increased at night. Lysosomal enzyme and alkaline phosphatase concentrations in epiphyseal cartilage usually showed 2 activity peaks, i.e. in the middle of the day and at night, vs a single peak in articular cartilage and cortical bone at night. Immobilization (2 days) caused significant elevations of most enzymes in night active tissues and abolished the rhythmic growth patterns. © 1979.