The establishment of a new biological assay system for simultaneous measurement of bone resorption and bone mineralization in organ cultures of chick embryonic femur.

A biological assay system has been developed for the simultaneous measurement of bone resorption and bone mineralization. In this system we (1) used chick embryonic femur as the biological material because of the easy handling and easy specification of developmental stages compared with rat and mouse, (2) labeled bone with 45Ca in vitro, (3) calculated the biological half life (T1/2) of 45Ca incorporated into bone salts for quantitative estimation of the bone resorbing activity, and (4) investigated bone-mineralizing activity by determining the calcium content before and after cultivation. Eleven-day-old chick embryonic femur was labeled with 45Ca in a chemically defined medium in vitro and thereafter labeled bones were transferred to chase medium. T1/2 was calculated from the sequential release of the label into the medium from the cultured bone. No one heretofore had determined the T1/2 of Ca in bone salts. We first determined in this study that the T1/2 of Ca in the chick embryonic femur is about 50 h. The decrease in T1/2 by parathyroid hormone, prostaglandin E1 and E2 and lipopolysaccharide, well-known stimulators of bone resorption, showed that this system works well in terms of bone resorption. By using this system, we demonstrated that immunomodulators such as Bacillus Calmette Guerin and Corynebacterium paruvum stimulate bone resorption and therefore affect bone metabolism. On the contrary, sodium fluoride (NaF) and hydrocortisone increased T1/2, indicating that they inhibit bone resorption. These agents were also tested to determine if they would alter total calcium in the bone during cultivation.(ABSTRACT TRUNCATED AT 250 WORDS)