Effects of B-aminopropionitrile on mineralization during endochondral ossification in chick tibia.

Two-week-old white leghorn chicks were fed a diet containing BAPN (0.05%) for three weeks. Thirty-six hours before sacrifice, the controls and BAPN fed chicks were dosed with 35S. The zone of provisional calcification was isolated, and 35S incorporation was estimated by liquid scintillation counting. Alkaline phosphatase and Ca+2-ATPase were biochemically analyzed. Microdensitometry, to assess the level of mineralization, was done on epiphysis and the metaphysis. Morphometry was performed on the various zones of growth plate. 35S incorporation was significantly lower in the bones of BAPN treated chicks as compared to the controls. The enzymatic studies showed a significant inhibition of alkaline phosphatase and Ca+2-ATPase. The microdensitometric studies showed a smaller area of highly mineralized bone in the zones of provisional calcification of the BAPN treated chicks as compared to the controls. Morphometry showed a reduction in the width of the zone of calcification in BAPN treated chicks as compared to the controls. On the basis of the above data, it is suggested that BAPN induced inhibition of mineralization during endochondral ossification may be the result of a lower synthesis of sulfur containing GAG's, the inhibition of enzymes alkaline phosphatase and Ca+2-ATPase and the derangement of cellular zones of the growth plate. The implications of these results lie in the fact that mineralization is dependent on multifactorial control of the microenvironment of bone and cartilage.