The response of bone apposition rate to some nonphysiologic conditions

The response of bone apposition to some nonphysiologic conditions was investigated. In rabbits, the normal osteogenic rhythm was totally abolished shortly following treatment of hydrocortisone at a dose of 2 mg/kg body weight daily. A new rhythm developed after the treatment was continued for 20 1/2--34 days. The rate of bone apposition was significantly depressed compared to normal data reported previously. In rats receiving one U.S.P. unit of parathyroid extract daily for 14 days, the rate of bone apposition was significantly higher than that in control rats. In both sepcies, the response to an exogenous hormone was identified for all skeletal locations. It was concluded that new bone apposition was a function of activated osteoblasts, and that this function responded only to general body control mechanisms.