Perichondrial localization of ETA receptor in rat tracheal and xiphoid cartilage and in fetal rat epiphysis.

Autoradiographic studies using 125I-labeled endothelin-1 (ET-1) on sections of rat cartilage tissues, including the trachea, xiphisternum, and fetal rat epiphysis, revealed dense localization of endothelin receptors in the perichondrium. In contrast, the binding of ET-1 was not detected in the chondrocytes, cartilage matrix, and other connective tissues of the cartilage tissues tested. The perichondrial binding of 125I-ET-1 was completely abolished with BQ-123 [an endothelin receptor subtype A (ETA) antagonist] but not with BQ-3020 (an ETB agonist), and we demonstrated the perichondrial localization of ETA receptors. [3H]thymidine incorporation in vitro was significantly increased in rat xiphoid cartilage tissues exposed to ET-1. These findings suggest that the ET-1/ETA receptor system plays an important role in regulating cartilage metabolism and endochondral bone formation.