Stretching of fetal membranes increases the concentration of interleukin-8 and collagenase activity.

Objective: The aim of this study was to determine whether stretching of fetal membranes can increase interleukin-8 concentration and collagenase activity.
Study Design: Strips of whole fetal membranes, amnion, or muscles of the lower uterine segment were stretched for 2 or 4 hours. Interleukin-8 and collagenase activity were measured in homogenized control and stretched samples. Immunohistochemical staining for interleukin-8 was carried out.
Results: The interleukin-8 concentration increased significantly after the whole fetal membranes were stretched for 2 and 4 hours (p <0.0007 and 0.001, respectively). Also, stretching of amnion and muscles of the lower uterine segment for 2 and 4 hours increased the concentration of interleukin-8 significantly (p <0.0007 after 2 and 4 hours, respectively). Collagenase activity was significantly increased after stretching of amnion, amniochorion, and muscles of the lower uterine segment for 4 hours (p <0.0007, 0.006, and 0.0007, respectively). After stretching, samples were darkly stained for interleukin-8 compared with control nonstretched samples.
Conclusion: Stretching of amnion, amniochorion, and muscles of the lower uterine segment increased interleukin-8 production and collagenase activity.