Different localization of ETA and ETB receptors in the hyperplastic vascular wall

We investigated which subtypes of endothelin-1 (ET-1) receptors are involved in the pathogenesis of angioplasty-induced lesion formation in the rabbit carotid artery. Four weeks after removing endothelial cells (EC), we noted a marked intimal hyperplasia. The Bmax values for [125I]ET-1 and [125I]IRL1620 (an agonist for the ETB receptors) bindings were greater in the hyperplastic artery, without changes in Kd values. [125I]ET-1 binding was completely inhibited by unlabeled ET-1 and Ro 46-2005, a mixed-type antagonist for the ETA and ETB receptors, but partially by BQ123, a selective antagonist for ETA receptors, and IRL1620. The [125I]ET-1 binding sites not inhibited with BQ123 were significantly increased in the hyperplastic artery. The binding study suggested the presence of non-ETA/non-ETB receptors. The rank order of the increasing ratio in the density of receptors was ETB > putative non-ETA/non-ETB > total ET-1 receptors > ETA. The histochemical experiments with biotinylated ET-1 at lysine-9 side chain alone or in combination with unlabeled ET-1, BQ123, Ro 46-2005, or IRL1620, showed the ETA receptors to be localized mainly in the media, whereas the ETB receptors localized mainly in the neointima. These results suggest that the increased ET-1 receptors, especially ETB and/or putative non-ETA/non-ETB, are closely related to the occurrence of the intimal hyperplasia after endothelial removal.