CIRCADIAN VARIATION IN BONE-RESORPTION IS NOT RELATED TO SERUM CORTISOL

Serum osteocalcin, serum procollagen type I carboxyterminal propeptide (sPICP), and the urinary excretion of pyridinium crosslinks (biochemi cal markers of bone formation and resorption) all exhibit a circadian variation with a peak during the night, This study was performed to in vestigate the influence of the endogenous circadian rhythm in cortisol on the biochemical markers of bone turnover, Participants included II patients substituted with hydrocortisone due to either hypopituitaris m (n = 7) or bilateral adrenalectomy (n = 4), Their daily tablet intak e of hydrocortisone was divided in four equal doses in order to abroga te the known circadian variation in cortisol, 24 healthy postmenopausa l women served as controls, The study design was performed over 24 h, with blood samples taken every 3 h, and urine collected in 3 h aliquot s, Urinary pyridinium crosslinks (Pyr/Cr, D-Pyr/Cr), serum osteocalcin (sOC), and serum PICP were measured, Patients without a circadian var iation in cortisol had normal circadian variation in the urinary excre tion of pyridinium crosslinks and sPICP, but no circadian rhythm in se rum osteocalcin, We conclude that the etiology of the circadian rhythm in the biochemical markers of bone turnover is still unknown, This st udy indicates that the circadian variation in sOC can be controlled by the endogenous circadian variation in serum cortisol, whereas this ho rmone does not control the circadian variation in either the serum PIC P or the urinary excretion in pyridinium crosslinks. (C) 1997 by Elsev ier Science Inc. All rights reserved.