Involvement of tachykinin NK1 and NK2 receptors in changes in lung mechanics and airway microvascular leakage during the early phase of endotoxemia in Guinea pigs

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Abstract
We investigated the role of tachykinins in airway neurogenic responses occurring in the early phase of endotoxemia. Forty-eight anesthetized guinea pigs were evenly divided into six groups pretreated with either saline vehicle, CP-96,345 (a tachykinin NK1 receptor antagonist), SR-48,968 (a tachykinin NK2 receptor antagonist) or CP-96,345 and SR-48,968 in combination. Animals then received an intravenous injection of either saline (the vehicle for endotoxin) or endotoxin (30 mg/kg). Total lung resistance (RL) and dynamic lung compliance (Cdyn) were continuously measured before and 30 min after administration of saline or endotoxin. Airway microvascular leakage was assessed at the end of the observation period. Endotoxin significantly increased RL and decreased Cdyn 10 min after intravenous endotoxin injection. Plasma extravasation significantly increased in the trachea, main bronchi and intrapulmonary airways with endotoxin administration. These changes in lung mechanics were abolished by SR-48,968, but were unaffected by CP-96,345. The plasma extravasation was largely attenuated by CP-96,345 and/or SR-48,968. We conclude that (1) endogenous tachykinins play an important role in producing changes in lung mechanics and airway microvascular leakage during the early phase of endotoxemia and (2) activation of tachykinin NK2 receptors is responsible for the former response, while activation of both tachykinin NK1 and NK2 receptors is involved in the latter response.