Diurnal variation in concentrations of various markers of bone metabolism in dogs

Objective-To evaluate diurnal variation in concentrations of selected marke rs of bone metabolism in dogs. Animals-Ten 3- to 4-year-old ovariectomized Beagles. Procedure-Blood and urine samples were obtained in the morning before dogs were fed (8 AM) and then at 2-hour intervals for 24 hours. This procedure w as repeated 2 weeks later. Concentrations of osteocalcin (OC) and carboxy t erminal telopeptide of type-I collagen (ICTP) were measured in serum, using a radioimmunoassay; concentrations of hydroxyproline (HYP), pyridinoline ( PYD), and deoxypyridinoline (DPD) were analyzed in urine. Hydroxyproline co ncentration was measured by means of a colorimetric test, whereas PYD and D PD concentrations were quantified by use of high-performance liquid chromat ography. Results-In both parts of the study, HYP concentrations increased significan tly, compared with values before feeding, until 8 hours after feeding; HYP concentrations then returned to prefeeding values. Concentrations of DPD an d PYD decreased from before feeding until 2 PM and then increased until 8 P M. The ICTP concentrations slowly decreased until 4 PM but returned to pref eeding values thereafter. In both parts of the study, concentrations of OC decreased during the day and then increased to reach values similar to thos e obtained before feeding. Conclusions-Changes in the concentrations of bone markers were detected thr oughout the day in the dogs of this study. Increase in HYP concentration mo st likely was related to feeding. As documented for bone resorption and for mation in other species, circadian rhythms were evident for concentrations of DPD, PYD, and OC. Investigators should consider the time of sample colle ction when measuring these markers.