Studies on Collagen in the Human Uterus

Its Biochemical Changes during Pregnancy, Delivery and Postpartum Involution

Abstract

In order to study the physiological changes in collagen of the human pregnant and postpartum uterine tissue, the hydroxyproline content, the solubility of collagen and the activities of prolyl hydroxylase in the samples obtained from the cervix and the body of the normal human uterus were studied. The results were as follows : 1. Hydroxyproline contents in the uterine cervix during pregnancy and postpartum were slightly less than that of nonpregnant controls. The lowest level was observed immediately after delivery, but, on the fourth day postpartum, it increased to more than that obtained immediately after delivery. In the uterine body, there was no remarkable change in its content during pregnancy, but it decreased remarkably immediately after delivery. 2. Pepsin-soluble collagen in the uterine cervix increased significantly immediately after delivery compared with nonpregnant controls, but, on the fourth day postpartum, it decreased significantly compared with that immediately after delivery. In the uterine body, no significant change in solubility was observed throughout pregnancy. 3. Prolyl hydroxylase activity in the uterine cervix was slightly elevated during pregnancy and at the time of delivery, and the highest level was observed on the fourth day postpartum. On the other hand, in the uterine body the highest activity was observed immediately after delivery. 4. The stimulative or suppressive effects on proliferation of fibroblasts cultured in vitro were observed in two groups administered 17β-estradiol or estriol, respectively. They were considered presumably due to the difference of doses between the two steroids used. Progesterone showed a more suppressive effect on cell proliferation. These findings suggest that there are significant and definite biochemical changes in human uterine collagen during pregnancy, at the time of delivery and the postpartum period under the presumptive effects of female sex steroids. And, from these data, one can also deduce that collagen might play an important role in the enlargement and distention of the uterine body, softening of the cervix and postpartum involution.