CHANGES IN THE CARBOXYL-TERMINAL PROPEPTIDE OF TYPE-I PROCOLLAGEN ANDOTHER MARKERS OF BONE-FORMATION UPON 5 DAYS OF BED REST

This study was performed in order to investigate the influence of skel etal unloading on the serum concentration of the carboxyl-terminal pro peptide of type I procollagen (sPICP) and other markers of bone format ion. Blood samples were taken every third hour from nine healthy preme nopausal women (22-29 years) in two 24 h studies, before and at the en d of five days of bed rest. Furthermore, a set of samples were taken 1 2 h apart after three days of bed rest. We measured sPICP, the serum c oncentration of intact and N-terminal-Mid fragment osteocalcin (sOC), and the serum concentration of alkaline phosphatase (sAP). During the five days of bed rest a gradual increase in sOC was observed, while sP ICP gradually decreased. sAP was unchanged. Five days of best rest res ulted in the following overall changes in the 24 h mean values: sPICP: -14% (p = 0.002); sOC: +9% (p = 0.009); sAP: -1% (not significant). T he circadian patterns did not change significantly after bed rest. It is puzzling that the changes in the bone formation markers are of diff erent magnitude, and for sPICP and sOC even in opposite directions. Th e increase in sOC may be caused by an increase in OC secretion by the osteoblasts or a release of bone-incorporated OC from resorbing sites; the accompanying decrease in sPICP may indicate that bone formation i s actually transiently decreased after short term bed rest.