Using Wistar male rats, the effects of thyroxine (T4) on the levels of bone γ-carboxyglutamic acid-containing protein (BGP) in bone, serum, and urine were observed in relation to those of calcium metabolism. T4-treatment increased serum and bone BGP levels in 2 weeks with the increase of bone-origin serum alkaline phosphatase activity indicative of the activity of bone formation. After 7 weeks treatment of T4, no significant change was observed in these levels, however a significant loss of travecular bone was observed in T4-treated tibia. Moreover, the excretion of urinary calcium and inorganic phosphorus was stimulated by T4-treatment with the increase of urine BGP excretion. These results suggest that BGP level in urine, as well as in serum, reflects bone metabolism.
