Inhibition of bradykinin‐evoked trigeminal nerve stimulation by the non‐peptide bradykinin B2 receptor antagonist WIN 64338 in vivo and in vitro

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Abstract
1 This study investigated the effect of the recently described non-peptide bradykinin B2 receptor antagonist, WIN 64338 ([[4-[[2-[[bis(cyclohexylamino)methylene]amino]-3-(2-naphthalenyl)-1-oxopropyl] amino]phenyl]methyl]tributylphosphoniumchloride monohydrochloride), in experimental models of bradykinin-evoked sensory nerve stimulation. 2 In the rabbit isolated iris sphincter in vitro, bradykinin-evoked contractile responses are mediated via tachykinins released from peripheral endings of the trigeminal sensory nerve. WIN 64338 (1 – 10 μm) competitively antagonised contractile responses to bradykinin with a pKB estimate of 6.6 ±0.1 (n = 11). The antagonism was selective since WIN 64338 (10 μm) did not significantly inhibit submaximal contractile responses to the direct-acting spasmogens substance P (10 nM), neurokinin A (3 nM), substance P methyl ester (10 nM) or senktide (100 nM); nor by sensory non-adrenergic non-cholinergic nerve stimulation evoked by capsaicin (10 μm), or electrical field-stimulation (3, 10, 30 Hz) (P>0.05; n = 3–11). 3 Topical application of bradykinin to the conjunctiva and to the nasal mucosa of the guinea-pig in vivo causes plasma extravasation predominantly via the release of tachykinins from peripheral endings of the trigeminal nerve. The increases in plasma extravasation (measured by extravasation of Evans blue dye) induced by bradykinin in the guinea-pig conjunctiva (20 nmol) and nasal mucosa (50 nmol) were markedly reduced (by 81 ± 3% and 69 ± 5%, respectively) following pretreatment with WIN 64338 (30 nmol kg−1, i.v.) (n = 5–6; P−1, i.v.; n = 5–6). This inhibition was selective since at 300 nmol kg−1, WIN 64338 did not inhibit plasma extravasation evoked by substance P in the conjunctiva (5 nmol; P0.05; n = 5). 4 This study demonstrates that WIN 64338 is a selective and competitive bradykinin B2 receptor antagonist and can be useful for analysing bradykinin-evoked trigeminal nerve stimulation both in vitro and in vivo.