CIRCADIAN-RHYTHM IN TYPE-I COLLAGEN FORMATION IN POSTMENOPAUSAL WOMENWITH AND WITHOUT OSTEOPENIA

A circadian rhythm in the serum concentration of the procollagen type I carboxyl-terminal propeptide (sPICP) has previously been demonstrate d in premenopausal women. This study was performed to investigate the circadian rhythm in sPICP in healthy and osteopenic postmenopausal wom en. Blood samples were taken every third hour for 27 h from three grou ps of women: 12 early postmenopausal women (aged 55 +/- 2 years; mean +/- SD); 12 late postmenopausal women (aged 73 +/- 1 years); and 12 os teopenic but otherwise healthy late postmenopausal women (aged 73 +/- 1 years). A circadian rhythm in sPICP was found in all three groups, a s shown by cosinor analysis (p = 0.000003-0.03). The circadian rhythm in sPICP was significantly different between the osteopenic group and the age-matched healthy group (p <0.008). The amplitude of the circadi an rhythm in sPICP was about twice as high in the osteopenic group, an d the time of the maximum tended to be about 3 h later, as compared wi th the age-matched healthy group. The plasma concentration of osteocal cin, as measured by a recently developed two-site enzyme-linked immuno sorbent assay, also showed a circadian rhythm in all three groups (p = 0.0001-0.05), with no significant differences between groups. In conc lusion, we have found a significant circadian rhythm in sPICP in both early and late postmenopausal women. In osteopenic women the nightly p eak in sPICP is larger and persists later into the night as compared w ith non-osteopenic women.