Endothelin transfer and endothelin effects on water transfer in human fetal membranes

Although endothelin-1 is synthesized by human amnion, its physiologic role and its ability to be transferred to myometrium for oxytocic action remain unclear. We investigated the transfer of endothelin-1 itself and the effects of endothelin-1 on the transfer of tritiated water across human amnion or amnion/chorion/decidua in vitro with an Ussing chamber technique. Permeability coefficients (mean ± standard error) for ³H₂O across amnion/chorion/decidua in the fetal to maternal direction were 1.26 ± 0.21 and 1.25 ± 0.10 x 10^-4 cm/second (N = 6) and in the maternal to fetal direction 0.90 ± 0.07 and 0.98 ± 0.15 x 10^-4 cm/second (N = 5) in the absence or presence, respectively, of 10^-9 mol/L endothelin-1 in the fetal reservoir. Comparable values were found in either direction with 10^-9 mol/L endothelin-1 in the maternal reservoir. Apparent permeability coefficients for ¹²⁵I endothelin-1 in the fetal to maternal direction were 3.34 ± 0.79 and 2.43 ± 0.68 x 10^-5 cm/second (N = 5) for amnion or amnion/chorion/decidua. However, appreciable trapping of ¹²⁵I endothelin-1 by the fetal membranes was apparent. Endothelin-1 does not appear to affect water movement across the human fetal membranes, and only a small proportion of endothelin-1 itself is transferred across the membranes.