Phasic production of urinary pyridinium crosslinks in mice: The effect of ovariectomy

Considerable sample to sample variability in deoxypyridinoline crosslink/creatinine (Dpd/CREAT) ratio values was confirmed when twice-weekly sampling for 77 days was performed in C57 mice. Analysis of samples from individual mice indicated that, in the majority of mice in a given group (54–67%), phasic changes occurred with periodic peaks as much as 4–5 times basal values. Alignment of peaks in the individual time courses of mice revealed a clear cyclic crosslink production (periodicity 12–14 days) for the population, although not all mice gave a peak in every case. Ovariectomy (OVX) (compared to sham-operated mice) increased mean values of crosslink production by either C57 or C57 × 129 F1 mice from about 10 days after operation with highest values between 21 and 35 days, and then a decrease in the difference between sham and OVX, particularly in C57 mice. Analysis of both time courses for individual mice and distribution curves of the data from groups of mice indicated that OVX consistently increased basal crosslink values (6–9 ratio units) with phasic peak values superimposed. The peak alignment analysis reinforced this observation. The influence of the background variability was avoided by pooling data over one cycle time and the use of nonparametic statistics, and the effect of OVX was analyzed in several strains of mice. Crosslink levels and phasic production declined with age but were also influenced by manipulation of the mice, suggesting that experimental conditions should be rigorously controlled when this urinary crosslink measure is used as a parameter in mouse models of OVX-induced osteoporosis.