Effect of Endothelin Receptor Antagonist Bosentan on Chronic Hypoxia-Induced Inflammation and Chemoafferent Neuron Adaptation in Rat Carotid Body

Chronic hypoxia (CH) induces an inflammatory response in rat carotid body that is characterized by immune cell invasion and the expression of pro-inflammatory cytokines. In the present study, we have investigated the role of type-A endothelin (ET-A) receptors in the development of CH-induced inflammation. After 7 days of CH (380 Torr), double-label immunofluorescence studies demonstrated elevated levels of ET-A receptor and tyrosine hydroxylase (TH) in O(2)-sensitive type I cells. Following CH, ET-A receptors were also expressed on resident and invasive CD45+ immune cells distributed in tissue surrounding chemosensory cell lobules. Immnofluorescence and quantitative PCR studies showed that concurrent treatment with the ET-A/B receptor antagonist, bosentan (200 mg/kg/day), blocked CH-induced ED-1+ macrophage invasion and the upregulation of cytokines, including interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor α (TNFα), and monocyte chemoattractant protein-1 (MCP-1). Moreover, bosentan treatment blocked the CH-induced increases in expression of acid-sensitive ion channels (ASICs) in chemoafferent neurons in the petrosal ganglion (PG). Our findings are consistent with the hypothesis that CH-induced inflammation involves the upregulation and release of ET-1 from type I cells. ET-1 may act in an autocrine/paracrine mechanism via ET-A receptors on chemosensory type I cells and immune cells to promote an inflammatory response.