Localization and role of endothelin-1 and endothelin receptors in the human Fallopian tube

The present experiments were designed to investigate the localization and role of endothelin-1 (ET-1) and endothelin receptors (ETA and ETB) in human Fallopian tubes obtained from patients in the follicular phase. Immunohistochemical studies revealed the predominant localization of ET-1 and of ETB receptors in the tubal epithelium and also within the muscle layer to a lesser degree. ETA receptors were dominant within the muscle layer. Scatchard plot analysis of the [(1I5)1]ET-1 binding also revealed the localization of ETA and ETB receptors on the Fallopian tubal membrane. A dissociation equilibrium constant of 34.6 +/- 3.3 pmol/l and a maximum binding site concentration of 1137.0 +/- 239.1 fmol/mg protein were obtained from the Scatchard plot analysis. Treatment of Fallopian tubal strips with ET-1 produced a tonic contraction which was inhibited by an ETA antagonist but not by an ETB antagonist. However, the increase in frequency and decrease in amplitude of rhythmic contractions caused by ET-1 were modulated by the ETB antagonist but remained unaffected by the ETA antagonist. These results suggest that ET-1 modulates the motility of the Fallopian tube through excitation of ETA and/or ETB receptors and possibly plays some role in oocyte capture.