Unusual vascular responses in the umbilical artery, mediated by endothelin-like receptors

Abstract: In this present study the population of endothelin-like receptors in the human umbilical artery was examined in vitro in different parts of the umbilical cord. Immunohistochemistry revealed ETB receptors in the endothelium and an uneven distribution of ETA receptors in the smooth muscle of the arterial wall, when comparing different parts of the umbilical artery. ET-1 induced vasoconstriction was effectively antagonized by BQ123 in the middle portion, but not close to baby. BQ788 had no effect on contracions induced by neither ET-1 nor sarafotoxin S6b in the arterial segments close to baby. High concentrations of PD 142893 markedly decreased the contractions effectuated by ET-1, whilst low concentrations had no effect. PD142893 in lower concentrations increased the contractions caused by sarafotoxin S6b, whereas high concentrations left the contractions unaffected. Destruction of the endothelium abolished this potentiating effect of PD142893. In segments precontracted with 5-HT, did the addition of PD142893 to sarafotoxin S6b in combination with BQ123 lead to deprivation of the otherwise noted small relaxation. Indomethacin and L-NMMA both potentiated the contractions induced by ET-1 whereas the contractions elicited by sarafotoxin S6b were attenuated. L-arginine counteracted the augmentive effects of L-NMMA on the contraction elicited by ET-1. L-arginine did not affect the L-NMMA induced inhibition of the contraction elicited by sarafotoxin S6b, but had an inhibitory effect per se on the contractions induced by both ET-1 and sarafotoxin S6b. The contractions induced by ET-1 were promoted by a higher oxygen tension.