Increase in urinary desmosine and pyridinoline during postpartum involution of the uterus in humans.

One of the most rapid changes in collagen and elastin content of a tissue occurs in the uterus following postpartum involution. We measured the urinary excretion of specific amino acid markers for mature elastin (desmosine [DES] and isodesmosine [IDES]) and fibrillar collagen (hydroxylysyl pyridinoline [HP] and lysyl pyridinoline [LP]) before and after parturition in three gravid subjects. For that purpose, we used an isotope dilution method coupled with gel filtration and HPLC. The highest DES values were found 2-5 weeks postpartum and were 18-45 micrograms/g creatinine or two to six times those found for healthy neversmoking nongravid females (7.7 +/- 0.3 micrograms/g creatinine, mean +/- SE). The highest levels of urinary HP for each subject were found 2-3 weeks after parturition and were 115-607 nmol/mmol creatinine or 4-21 times those found for healthy neversmoking nongravid females (28.1 +/- 1.3 nmol/mmol creatinine). For the gravid subjects as a group and also for each subject, the mean values for urinary DES, IDES, HP, and HP/LP during the first 6 weeks postpartum were significantly greater than the mean baseline values beginning 27 weeks postpartum. For the gravid subjects as a group, the mean value for urinary HP/LP during the first 6 weeks postpartum was significantly greater than the value during the 20 weeks preceding parturition. This suggested that the tissue(s) of origin of the excess HP, during the 6 weeks following parturition, was not bony and was consistent with a uterine origin.