To determine the localization of endothelin binding sites and immunoreactivity in human synovial tissues.
Quantitative in vitro autoradiographic and immunohistochemical techniques were used to localize and characterize 125I-labeled endothelin-1 (125I-ET-1) binding sites and endothelin-like immunoreactivity in sections of rheumatoid, osteoarthritic, and normal synovium.
Specific 125I-ET-1-binding sites, characteristic of the ETA receptor, were localized to the media of synovial blood vessels in all 3 groups. No difference was found in vascular binding site density in rheumatoid and osteoarthritic synovium. Endothelin-like immunoreactivity was localized to endothelial cells in blood vessels displaying 125I-ET-1 binding sites.
We conclude that endothelin may act locally, modulating synovial perfusion and exacerbating hypoxia in chronic arthritis.