Evidence for the coupling of bone formation to bone resorption in vitro

An in vitro organ culture system of embryonic chick tibiae was used to examine bone formation and bone resorption under conditions of stimulation with 10^-12 M parathyroid extract. The bones were cultured in a serum-free medium to alleviate any potential interference by serum growth factors. Evidence is presented showing that this bone culture system responds to parathyroid extract with an increase in both bone resorption and bone formation. Although initially there was a decrease in formation, this was followed after 12-16 h by an increase in formation which was correlated with resorption (r = .96, p < .05). These results suggest that the increase in formation was some consequence of the increase in resorption, and as such are consistent with the interpretation that coupling can occur in vitro.