Changes with age in the urinary excretion of lysyl- and hydroxylysylpyridinoline, two new markers of bone collagen turnover.

Two intermolecular cross-linking amino acids, hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP), are promising markers in urine of collagen resorption because their levels in urine should reflect only collagen resorption and, unlike hydroxyproline, should not be influenced by degradation of either newly synthesized collagen molecules or noncollagenous proteins. Changes with age in the urinary excretion of HP and LP were studied in 24 h collections of urine from a group of 22 male and 27 female healthy subjects aged from 2 to 70 years. The pyridinolines were quantitated, utilizing their natural fluorescence, after resolution by reversed-phase HPLC. Levels of both pyridinolines were higher in children than in adults, but in adults no evidence of age or sex variations were observed except in the 20-30 year age group. Mean values of HP/Cr and LP/Cr in 37 adults (21-70 years) were 27.2 +/- 1.9 and 8.8 +/- 0.8 mumols/mol, respectively; in the 12 children (2-15 years) the mean values were 14.4 and 12.4 times higher than the respective adult values. Making certain assumptions, the mean amount of bone resorbed in normal adults was tentatively estimated at 1.9 g per 24 h. The finding that differences between children and adults in these relatively specific markers were greater than with hydroxyproline suggests that hydroxyproline values may considerably underestimate the actual amount of bone turnover occurring in growing children or overestimate the adult turnover rate.

The effect of ruminal phosphate concentration on the absorption of calcium, phosphorus and magnesium from the reticulo-rumen of the sheep.

1. The absorption rates of calcium, inorganic phosphate (Pi) and magnesium were determined from buffered solutions placed in the temporarily isolated and washed reticulo-rumen of conscious sheep. The basic composition of these solutions was similar to that found in supernatant fractions of ultracentrifuged rumen contents. 2. The Pi concentrations studied in these solutions were 2, 8.7, 14, 17.3 and 38 mmol/l. The initial concentration of Ca was 2.0 mmol/l and that of Mg was 2.5 mmol/l in all experiments. 3. Increasing the Pi concentration in the rumen solution from 2 to 38 mmol/l resulted in increases in the net absorption rates of both Ca and Pi, and a decrease in the potential difference across the wall of the rumen. 4. Similarly, increasing the Pi concentration from 2 to 17.3 mmol/l resulted in an increase in the net absorption rate of Mg from the rumen. 5. Mineral analysis of strained rumen fluid or a 30,000 g centrifugate of strained rumen fluid revealed a reduced Pi concentration in sheep fed on frozen spring grass as opposed to the pellet + hay diet. The values obtained were within the range studied.