Changes in the Activities of Plasma Acid and Alkaline Phosphatases 185 



increasing osteoclast activity in the medullary bone reported by Bloom et al. (1958) 

 and Stringer (1962). 



The presence of acid phosphatase in regions of osteoclastic resorption has been 

 demonstrated histochemically by Schajowicz and Cabrini (1958) and since bone 

 trabeculae which are undergoing active ossification are rich in alkaline phosphatase 

 (SiFFERT, 1951; Heller-Steinberg, 1951; Pritchard, 1952), it may be inferred that 

 osteoblasts liberate this enzyme. It is not known, however, whether bone cells secrete 

 phosphatases when they are actively carrying out their normal metabolic functions, 

 whether these enzymes leak passively out of the cells or whether they are liberated 

 only when the cells degenerate. 



There is no direct evidence that the phosphatases studied in this experiment 

 originated in the bone but the fact that the changes in the plasma levels observed 

 during shell calcification did not occur in the absence of shell formation (Taylor 

 et al., 1965), point to the skeleton as the most likely source, and the remarkable 

 manner in which changes in the cell population of the medullary bone during shell 

 calcification were reflected in changes in the levels of plasma acid and alkaline phos- 

 phatase suggests that the osteoclasts and osteoblasts release their respective phos- 

 phatases during their active metabolic phases. 



Acid phosphatase is one of the most active of the enzymes found in the lysosomes 

 and a study of other lysosomal enzymes in the plasma of laying hens might be 

 expected to shed light on the possible role of these enzymes in the activity of the 

 osteoclast. Mr. K. M. L. Morris working in this Department has recently shown that 

 there is a sharp fall in the level of /^-glucuronidase following oviposition in the fowl. 



References 



Bell, D.J. : Tissue components of the domestic fowl. 4. Plasma alkaline phosphatase activity. 



Biochem. J. 75, 224 (1960). 

 — , and W. G. Siller: Cage layer fatigue in Brown Leghorns. Res. Vet. Sci. 3, 219 (1962). 

 Bloom, M. A., L. V. Domm, A. V. Nalbandov, and W. Bloom: Medullary bone of laying 



chidcens. Amer. J. Anat. 102, 411 (1958). 

 Heller-Steinberg, M.: Ground substance, bone salts and cellular activity in bone formation 



and destruction. Amer. J. Anat. 89, 347 (1951). 

 Pritchard, J. J.: A cytological and histochemical study of bone and cartilage formation in 



the rat. J. Anat. 86, 259 (1952). 

 Schajowicz, F., and R. L. Cabrini: Histochemical localization of acid phosphatase in bone 



tissue. Science 127, 1447 (1958). 

 SiFFERT, R. S.: The role of alkaline phosphatase in osteogenesis. J. exp. Med. 93, 415 (1951). 

 Stringer, D. A.: The chemistry and physiology of bone, with special reference to medullary 



bone in the fowl. Thesis. University of Reading 1962. 

 Taylor, T. G., A. Williams, and J. Kirkley: Cyclic changes in the activities of plasma 



acid and alkaline phosphatases during eggshell calcification in the domestic fowl. Canad. 



J. Biochem. 43, 451 (1965). 



