The effects of
bleomycin,
elastase and
infection on the tensile strength of rabbit fetal membranes and the structure of the elastic tissue of rabbit amnion were studied. The experimental subjects were rabbits to which
bleomycin (total dose, 20 mg) or
elastase (total dose, 60 mg) was administered from 18 days of pregnancy. In addition to the fetal membranes from these treated animals, fetal membranes with amniotic
infection induced by injection of Escherichia coli into the amniotic fluid (AF) of rabbits at 22 or 23 days of pregnancy were examined, and those from rabbits administered physiological
saline solution were used as controls. The results obtained were as follows. Determination of tensile strength of the fetal membranes revealed that the infected membranes had minimum
rupture pressure (18.67 +/- 6.30 mm Hg), followed by the
elastase administration group (46.67 +/- 3.51 mm Hg). The value in the
bleomycin administration group (99.67 +/- 12.89 mm Hg) was significantly higher than that in the control group (61.80 +/- 6.30 mm Hg). Histological changes in the fibroblast layer of these fetal membranes included elastic
fibrosis due to excessive
collagen production, which was mostly manifested as
fibrosis densa, in the
bleomycin administration group. In the
elastase administration group, the elastic fibers were eliminated or became minute, as in the
infection groups. The above results showed the adverse effects of
elastase and
bleomycin and the destructive effect of
infection on the growth and properties of elastic tissue in the amnion, suggesting their pathophysiological importance.