Figure 4. Changes in urinary levels of pyridinium cross-links. The amounts of pyridinoline (Pyr) and deoxypyridinoline (Dpyr) in 24-hour urine collections from rats were measured weekly from 5 to 20 wks by use of high-performance liquid chromatography (n = 7). The Pyr/Dpyr ratio was calculated from the results. Significant difference by Student’s t test is indicated by one asterisk (p < 0.05) or two asterisks (p < 0.01). (A) Pyr, (B) Dpyr, (C) Pyr/Dpyr ratio.