RELAXIN (HRLX-2)-INDUCED WEAKENING OF HUMAN FETAL MEMBRANES IN-VITRO

We examined the effect of human relaxin (hRLX-2) on the biomechanical properties of human fetal membranes in vitro. Intact chorioamniotic me mbranes were obtained from twelve elective cesarean sections before th e onset of labor. Membrane strips with a fixed width were biomechanica lly tested after incubation for 20 h with hRLX-2 in concentrations of 10(-7) mol/l and 10(-9) mol/l. Incubation with hRLX-2 (10(-9) mol/l) c hanged the load-strain values as the membrane stiffness was decreased by 19% when compared with controls: median 2.45 N (range, 0.81-4.31) v ersus 3.03 N (1.28-5.46), P = 0.02 (Mann-Whitney test). For descriptio n of the membrane material as such, the stress-strain values were calc ulated by dividing the load-strain values with the cross sectional are a of the membranes. Incubation with hRLX-2 (10-9 mol/l) decreased the tensile strength of the membranes by 30%-0.817 N/mm(2) (0.282-1.139) v s. 0.575 N/mm(2) (0.101-1.150), P = 0.03 - and reduced the elastic mod ulus by 31%-2.26 N/mm(2) (0.82-5.08) versus 1.57 N/mm(2) (0.51-3.71), P = 0.002. Less pronounced effects were found after incubation with hR LX (10(-7) mol/l). No quantitative or qualitative changes of the membr ane collagen were found after relaxin incubation. Although the mechani sm for rupture of the fetal membranes remains unknown, the present res ults suggest that relaxin might be involved in the process leading to rupture of the membranes.