High levels of serum collagenase in premature labor—a potential biochemical marker

An improved sensitive assay for collagenase, which uses [³Hltelopeptide-free collagen as a substrate, was used to measure changes in serum collagenase levels in 96 women and ten men (18-35 years old). Both latent and active forms of collagenase were detected in serum by molecular sieve chromatography; these forms had a relative molecular weight (M_r) of 65,000 and 45,000, respectively. Only latent collagenase was detected in crude serum after destroying inhibitors by treatment with 3 M potassium thiocyanate. Collagenase levels in males were lower than in nongravid females (34 ± 5 versus 53 ± 5 U/dL; mean ± SEM; 1 unit = 1 pg collagen digested per minute at 30C). During pregnancy there was no significant change in serum collagenase levels until the onset of spontaneous labor in full-term pregnancies (37-42 weeks), at which point there was a 66% increase over the nongravid level to a value of 88 ± 5 U/dL. There was a further rise at one day postpartum, and high levels continued for at least four days. Women in premature labor (24-36 weeks) exhibited an eightfold increase in the level of serum collagenase to 405 ± 110 U/dL; 16 of 17 patients in this group had collagenase levels above the 95th percentile for women at 16-40 weeks but not in labor. This evaluation of serum collagenase may provide a key for detecting premature labor. It is suggested that the increase in serum collagenase arises from the lower uterine segment and cervix.