MINERALIZATION OF ALKALINE PHOSPHATASE-COMPLEXED COLLAGEN IMPLANTS INTHE RAT IN RELATION TO SERUM INORGANIC-PHOSPHATE

The present study was designed to determine the relationship between m ineralization of collagenous matrices and serum levels of calcium and inorganic phosphate. Collagen slices were prepared from bovine dentin or cortical bone and complexed with varying amounts of intestinal alka line phosphatase (ALP). The enzyme nas added to induce de novo mineral ization. The ALP-complexed slices were implanted subcutaneously over t he skull and in the dorsolateral aspect of the abdominal wall in femal e Wistar rats of various ages (5-, 10-, 20-, or 35-week-old) and in yo ung male rats fed on a low-P diet. After 1-4 weeks, the implants were removed and analyzed for calcium and phosphate content. In addition, s erum levels of calcium and phosphate (total and inorganic) were determ ined. It was shown that the highest mineral influx occurred in the you nger rats (which were also highest in serum P-i), whereas almost no mi neral uptake occurred in the older ones. Also in rats fed on a low-P d iet (which were low in serum P-i), a strongly decreased mineral influx was noted. In all animal groups a positive correlation was found betw een the degree of mineralization and serum P-i. No distinct relationsh ip was found between serum Ca/organic phosphate levels and mineral inf lux in the implants. In vitro incubation of ALP-collagen conjugates in serum from younger and older rats confirmed our view that serum P-i, besides local levels of ALP, is important in de novo mineral depositio n. For accretion of mineral in partially remineralized collagenous car riers, ALP activity was not required.