Diurnal periodicity in the metabolic activity of bone tissue1

SIMMONS, DAVID J., AND GEORGE NICHOLS, JR. Diurnal periodicity in the metabolic activity of bone tissue. Am. J. Physiol. LO(Q): 411-418. 1966. -Studies of the metabolism of bone cells in the metaphyses of the rat femur (distal) and tibia (proximal) have established that collagen synthesis and new bone formation is diurnally regulated. Significantly greater amounts of glycine-Q-Cl4 were initially incorporated by osteogenic cells in vivo during the environmental light period (ELP: og : 00-2 I : 00) than during the environmental dark period (EDP : 2 I : oo-og : 00). “Spot checks” of the metabolism of rat metaphyseal bone chips were made at the hours when the in vivo differences were most marked. The cells in bone incubated in vitro during the ELP (1000) exhibited a significantly greater uptake of glycine-1 -C14, RNA concentrations, and rate of collagen formation than cells incubated during the EDP (0300). Cell DNA concentrations were constant at these hours. Cell lactate production (tibias) and calcium concentrations in the incubation medium (femurs-tibias) were also higher at IO :oo --the hour of peak osteoclast frequency in histologic preparations. It was concluded that the period of most intense metaphyseal bone remodeling in rats occurred early during the ELP.