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 (ET(A) and ET(B)) in human Fallopian tubes obtained from patients in the follicular phase. Immunohistochemical studies revealed the predominant localization of ET-1 and of ET(B) receptors in the tubal epithelium and also within the muscle layer to a lesser degree. ET(A) receptors were dominant within the muscle layer. Scatchard plot analysis of the [(125)I]ET-1 binding also revealed the localization of ET(A) and ET(B) 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 ET(A) antagonist but not by an ET(B) antagonist. However, the increase in frequency and decrease in amplitude of rhythmic contractions caused by ET-1 were modulated by the ET(B) antagonist but remained unaffected by the ET(A) antagonist. These results suggest that ET-1 modulates the motility of the Fallopian tube through excitation of ET(A) and/or ET(B) receptors and possibly plays some role in oocyte capture.