Hydroxyproline excretion and collagen catabolism in rats of different age groups

Hydroxyproline as an index of collagen catabolism was studied in 432 urine samples collected from rats of different age groups at 4-hr intervals during the 24-hr period. The results showed statistically significant circadian rhythm in urinary hydroxyproline excretion with a peak between 2200 and 0200. The amount excreted is significantly more during the dark hours which can be correlated with the activity cycle. Total amount of excreted hydroxyproline decreases with age. The present results clearly show the importance of the determination of urinary hydroxyproline over a 24-hr period for clinical purposes