THE RENAL CLEARANCE OF FREE AND CONJUGATED PYRIDINIUM CROSS-LINKS OF COLLAGEN

We developed a sensitive reversed-phase high performance liquid chroma tography (HPLC) assay to measure free and total Pyridinoline (Pyr) and Deoxypyridinoline (Dpyr) in serum. The method was used to measure tot al serum levels in seven premenopausal women (ages 52.2 +/- 2.4 years) and to investigate the renal clearance of free and conjugated Pyr and Dpyr in two groups of children (group 1: 13 girls, ages 11-13 years; group 2: 18 older children [2 male, 16 female], ages 13-18 years). Blo od and 24-h urine samples were collected from the younger group to mea sure the renal clearance, and blood and 2-h morning urine samples from the older group were collected to investigate the fractional clearanc e. Total Pyr and Dpyr in the premenopausal women was 4.08 +/- 0.91 and 1.18 +/- 0.39 nmol/l, respectively. Free and total Pyr and Dpyr in se rum and urine was elevated in both groups of children. The free serum levels were 16 and 18% in young and older children, respectively, comp ared with 40 and 46% in the urine, The percentage of free Dpyr in seru m decreased with total urinary Pyr excretion (r = -0.56, p < 0.005, n = 31), The renal clearance of the free cross-link fraction in both gro ups was 4-fold higher than the conjugated fraction. The fractional cle arance of the free fraction was greater than 1 (p < 0.001) and the con jugated fraction less than 1 (p < 0.001), The fractional excretion of free Dpyr increased with total urinary Pyr excretion (r = 0.66, p < 0. 005, n = 13). We conclude that HPLC can be used to measure free and to tal Pyr and Dpyr in serum and that some free Pyr and Dpyr excreted in urine is produced by the kidney.