Neuropeptide Y inhibits neurogenic inflammation in guinea pig airways

We examined the effect of neuropeptide Y (NPY) on neurogenic airway microvascular leakage. Male Dunkin-Hartley guinea pigs (250-350 g) were anesthetized with urethan (2 g/kg ip). The cervical artery and vein were cannulated for monitoring blood pressure and injecting drugs, respectively. Atropine and propranolol (each 1 mg/kg i.v.) were administered 30 min before the experiment. After pretreatment with saline (vehicle for NPY) or NPY (1-100 micrograms/kg i.v.), Evans blue dye (30 mg/kg iv) was administered. Then, bilateral vagal nerves were electrically stimulated (5 V, 7 Hz, 5-ms duration for 3 min) to induce airway plasma leakage. Airways were divided into four sections [trachea (Tr), main bronchi, central intrapulmonary airways (IPA), and peripheral IPA] and incubated in formamide (37 degrees C for 16 h). The concentration of Evans blue dye was measured by spectrophotometer. Furthermore, we examined the effect of NPY on exogenous substance P- (0.3 microgram/kg i.v.) induced plasma extravasation. Bilateral vagal stimulation significantly increased leakage of dye in Tr to peripheral IPA. NPY did not affect basal leakage but did significantly inhibit neurogenic plasma extravasation in a dose-dependent manner with maximal inhibitions of 42.3 (Tr), 67.7 (main bronchi), 38.2 (central IPA), and 26.3% (peripheral IPA) at 30 micrograms/kg. Exogenous substance P-induced plasma extravasation was not inhibited by NPY. We conclude that NPY inhibits neurogenic inflammation by prejunctional inhibition of neuropeptide release from airway sensory nerve terminals.