Decrease of ciliary beat frequency by platelet activating factor: protective effect of ketotifen

The ciliary beat frequency (CBF) of the tracheal epithelial cells controls in part the respiratory tract mucociliary transport efficiency. We investigated the effects on CBF of PAF-acether (PAF) and its metabolite/precursor lyso-PAF. Guinea-pig tracheal rings were incubated for 3 to 6h with 1 microM PAF (C16, C18, C16/C18: 80/20%), lyso-PAF C16 or lyso-phosphatidylcholine (LPC). CBF changes were assessed by microphotooscillography (mean number of measures per ring = 14). We also examined the effect on PAF-induced CBF changes of the PAF receptor-antagonist WEB 2086, the anti-asthmatic/anti-anaphylactic drug ketotifen and the anti-histamine H1 pyribenzamine. CBF of control rings exposed to vehicle only from 0 to 6h showed no significant statistical variations (hertz, mean +/- SEM): 10.8 +/- 0.1 (n of measures = 890). By contrast, 1 microM C16, C18, and C16/C18 PAF significantly inhibited CBF after 3 to 6h incubation. C16 and C16/C18 PAF were more potent than C18 PAF (8.8 +/- 0.2, n = 112, 8.7 +/- 0.2, n = 64, and 9.6 +/- 0.1, n = 537 respectively; ANOVA analysis, p < 0.001 from control). At the same concentration, lyso-PAF also inhibited CBF, 9.5 +/- 0.1 (n = 197, p < 0.001) but not LPC, 10.5 +/- 0.2 (n = 127). WEB 2086 inhibited lyso-PAF and C16/18 PAF-induced CBF decrease. Preincubation (20 min) with ketotifen but not with pyribenzamine (1 microM) also suppressed the CBF inhibitory effect of PAF and lyso-PAF. Incubation of [3H]PAF with tracheal rings from 10 min to 6h resulted in its partial metabolism (25%) into [3H]lyso-PAF and a compound with a short retention time (10 min). [3H]lyso-PAF incubated for 3h with tracheal rings was partially metabolized (10%) into [3H]PAF and a compound with a short retention time. The PAF-induced decrease of CBF is congruent with its influence on pulmonary clearance, possibly via a specific receptor, since WEB 2086 abolished the effect of PAF. The inhibition of the PAF-induced CBF decrease by ketotifen may contribute to the therapeutic properties of this antiallergic drug.