High glucose-6-phosphatase activity in osteoblasts in the metaphysis of femur of growing rats

Glucose-6-phosphatase (G6Pase) activity was examined cytochemically in the metaphysis of femurs of 3- and 7-day-old rats. G6Pase and hexokinase activities were also examined biochemically in the femur and tibia of 3-day-old animals. The reaction product for G6Pase activity was seen in the endoplasmic reticulum and nuclear envelope of all cell types composing the metaphysis. The amount of the reaction product was abundant in osteoblasts, moderate in osteocytes, and moderate to scarce in osteoclasts and capillary endothelial cells. Biochemical G6Pase activity in the bones was higher than that in the brain, submandibular gland, or pancreas of the animals. Hexokinase activity in the bones was not different from that in the submandibular gland, pancreas, or kidney. The activity ratio of G6Pase and hexokinase in the bones (0.603) was greater than that in the submandibular gland, pancreas, or brain and smaller than that in the kidney. Possible physiological significances of the higher G6Pase activity in osteoblasts are discussed.