Abstract
Objective
To evaluate diurnal variation in concentrations of selected markers 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 was repeated 2 weeks later. Concentrations of osteocalcin OC and carboxy terminal 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 concentration was measured by means of a colorimetric test, whereas PYD and DPD concentrations were quantified by use of high-performance liquid chromatography.
Results
In both parts of the study, hyp concentrations increased significantly, compared with values before feeding, until 8 hours after feeding; hyp concentrations then returned to prefeeding values. Concentrations of DPD and PYD decreased from before feeding until 2 pm and then increased until 8 pm. The ICTP concentrations slowly decreased until 4 pm but returned to prefeeding values thereafter. In both parts of the study, concentrations of oc decreased during the day and then increased to reach values similar to those obtained before feeding.
Conclusions
Changes in the concentrations of bone markers were detected throughout the day in the dogs of this study. Increase in hyp concentration most likely was related to feeding. As documented for bone resorption and formation in other species, circadian rhythms were evident for concentrations of DPD, PYD, and oc. Investigators should consider the time of sample collection when measuring these markers. (Am J Vet Res 1999;60:949-953)
