Procollagen-III peptide serum levels in Paget's disease of the bone.

A commercially available radioimmunoassay kit was used to determine aminoterminal procollagen-III peptide (pNcoll III) serum levels in patients with Paget's disease of the bone and control subjects. In patients with Paget's disease pNcoll III concentrations were significantly elevated. They decreased to varying degrees under chronic therapy with human and salmon calcitonin, disodium ethane 1-hydroxy 1,1-diphosphonate (EHDP), or a combination therapy of EHDP and human calcitonin. The results were compared with the effect on traditional biochemical markers of disease activity: serum alkaline phosphatase and urinary hydroxyproline excretion, both of which reacted more acutely to the various therapies than pNcoll III, although pretreatment correlations were close. The most probable source of pNcoll III is not the Pagetic bone per se, but the vascular, fibrous connective tissue replacing normal bone marrow.