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RAPID EFFECT OF PROGESTERONE ON TRANSEPITHELIAL RESISTANCE OF HUMAN FETAL MEMBRANES: EVIDENCE FOR NON‐GENOMIC ACTION

1 The factors that regulate human fetal membrane transport mechanisms are unknown. The aim of the present study was to investigate the effect of progesterone on transepithelial electrical resistance (RTE) in the human amniochorion. 2 Fetal membranes from uncomplicated term pregnancies were obtained immediately after vaginal or Caesarean deliveries. Intact pieces were mounted as planar sheets separating an Ussing chamber. Progesterone (10−4 to 10−7 mol/L), mifepristone (10−4 to 10−8 mol/L) and combinations of progesterone plus mifepristone were applied to the chambers facing the fetal or maternal sides of the membrane. The RTE was measured before and 1, 5, 10, 15, 20, 25, 30, 45 and 60 min after each solution was added (at 37°C). The RTE was calculated in Ω.cm2, according to Ohm's law. 3 The mean (±SEM) basal value of RTE before the application of any substance in all experiments was 29.1 ± 0.4 Ω.cm2.  The net change in the RTE (ΔRTE) in relation to the basal value was calculated in each experiment. Progesterone, mifepristone and the combination of progesterone and mifepristone induced a rapid, surge‐type increase in RTE during the 1st min on both sides of the membrane. The combination of progesterone plus mifepristone exerted a synergistic action. The effect was stronger on the fetal side than on the maternal side for all substances tested (P < 0.05). The highest ΔRTE during the 1st min on the fetal side was seen with the combination of progesterone plus mifepristone (4.0 ± 0.3 Ω.cm2) and the lowest ΔRTE occurred with mifepristone (1.5 ± 0.1 Ω.cm2). 4 The present results demonstrated that the RTE of human fetal membranes increases rapidly in response to progesterone. It is possible that changes in RTE play a role in the control of membrane permeability during pregnancy.