Skeletal alkaline phosphatase activity as a bone formation index in vitro.

These studies were intended to examine the relationship between skeletal collagen formation and skeletal alkaline phosphatase (ALP) activity in vitro. Embryonic chick calvaria were exposed to skeletal effectors (including high and low pH, a range of [pi] and [Ca], PTH, NaF, etc), and collagen formation was assessed by the incorporation of 3[H]-proline as 3[H]-hydroxyproline (3[H]-hyp). ALP activity was measured in the serum-free conditioned medium and in 20% butanol extracts of the bones. We found that ALP activity and 3[H]-hyp incorporation were coordinately increased from pH 5.5 to pH 7.2 (r = .99, P less than 0.001). Calvarial ALP was not increased in response to low [Pi], but low [Ca] increased ALP and coordinately decreased collagen formation (r = -.81, P less than 0.05). Although calvarial ALP and 3[H]-hyp incorporation were coordinately increased by NaF, vanadate, PGE2, calcitonin, and insulin, the slopes of the correlations were not the same for all effectors (eg, NaF: r = .97, P less than 0.01, slope = 0.90; vanadate, r = .95, P less than 0.005, slope = 0.20), indicating differential actions on ALP and 3[H]-hyp incorporation. When a variety of effectors, including low [Ca], were used to treat different groups of calvaria, ALP activity was not correlated with 3[H]-hyp incorporation (r = .35), but when the exposure to effectors was limited to a preincubation, or when the low [Ca] data were excluded, a correlation was observed (r = .87, P less than 0.001, and r = .64, P less than 0.02, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)