The concentration of collagen and the collagenolytic activity in the amnion and the chorion.

Fetal membranes obtained from second-trimester abortions, elective Caesarean sections and after normal deliveries were studied. The hydrolytic activity against a DNP-peptide expressing the collagen turn-over was found to be very high in the second trimester and relatively high at term of pregnancy. The activity in the chorion was twice that in the amnion. The concentration of another collagen-degrading enzyme, leukocyte elastase, which is present during inflammatory reactions was high at the site of rupture. The collagen concentration given as micrograms hydroxyproline per mg dry weight was unchanged throughout pregnancy and labour in both fetal membranes. The concentration in amnion was twice that in the chorion. After delivery, the collagen content given as microgram/cm2 in the chorion was decreased at the rupture line. This was due to decreased thickness of the membrane, whereas the hydroxyproline concentration (microgram/mg dry weight) was unchanged. The amnion was thinner than the chorion, but the decreasing collagen content (micrograms/cm2) at the rupture line was less pronounced. The thinning of especially the chorionic membrane might be secondary to the mechanical stress of pregnancy and labour and/or, as our results suggest, due to enhanced catabolism.