In vivo effects of endothelin A- and B-receptor antagonists in guinea pigs

Endothelin (ET)-1, a novel 21-amino acid constrictor peptide, has been recently reported to have a potential pathophysiological role in asthma. We hypothesized that ET-1 might affect guinea pig lung via different ET receptor subtypes, i.e., ETA and ETB, in vivo. To test this hypothesis, we investigated the effects of ET-1 on airways in anesthetized, open-chest, mechanically ventilated [frequency (f) = 1 Hz; tidal volume (VT) = 9 ml/kg; positive end-expiratory pressure (PEEP) = 4 cmH2O] guinea pigs in the absence or the presence of ETA and ETB selective antagonists, i.e., BQ-123 and BQ-788, respectively. We affixed alveolar capsules to the lungs to measure alveolar pressure and calculated the elastance of lung (EL) and the resistance of lung (RL), tissue (Rti), and airway (R(aw)) under control conditions and after intravenous administration of ET-1 (10(-8) mol/kg). ET-1 induced a concentration-dependent increase in RL, Rti, R(aw), and EL.BQ-123 (2 mg/kg) partially blocks delta RL and delta R(aw) during ET-1 induced constriction, while delta Rti and delta EL were not significantly affected. BQ-788 (2 mg/kg) significantly inhibited delta RL, delta Rti, delta R(aw), and delta EL during ET-1-induced constriction. The combination of BQ-123 and BQ-788 completely ablated the response to ET-1. These data suggest that both ET receptor subtypes, i.e., ETA and ETB, may have physiological roles in guinea pig airways in response to ET-1, a potential mediator of asthma.