CYCLIC CHANGES IN THE ACTIVITIES OF PLASMA ACID AND ALKALINE PHOSPHATASES DURING EGGSHELL CALCIFICATION IN THE DOMESTIC FOWL
Acid and alkaline phosphatases were assayed in 240 samples of plasma taken from laying hens at various stages of the laying cycle. The activity of both enzymes was minimal shortly after oviposition. Acid phosphatase values increased rapidly during the first 10 hours of shell formation and then more slowly, reaching a peak when shell calcification was completed. A precipitous fall occurred about the time of oviposition. The activity of alkaline phosphatase increased rapidly after oviposition, reaching a maximum 8–9 hours later when calcification of the next egg had been in progress 4–5 hours, and thereafter falling steadily throughout the main period of shell formation. No systematic changes were observed in the levels of either enzyme at successive bleedings when shell calcification was not in progress. Striking relations were observed between the cyclic changes in the levels of phosphatase activity in the plasma and the changes known to occur in the cell population of the medullary bone, the level of acid phosphatase paralleling the osteoclast activity and the alkaline phosphatase paralleling the osteoblast activity. It is suggested that the osteoclasts and osteoblasts release their respective phosphatase during their active metabolic phases.