ACETYLCHOLINE-INDUCED BRONCHOCONSTRICTION MODIFIED BY NOISE EXPOSURE IN NORMAL BUT NOT IN SENSITIZED GUINEA-PIGS

1 The acute (6 h) exposure of guinea-pigs to white noise (110 dB) as a stress stimulus, reduced bronchial reactivity to acetylcholine (Ach) (3 - 1000 mu g kg(-1) i.v.) in anaesthetized animals. 2 The hyporespon siveness to Ach in stressed animals was not confirmed in vitro on trac heal preparations (Ach 1x10(-9)-1x10(-4)g ml(-1)) and disappeared in v ivo when the animals were sensitized with ovalbumin (OA, 100 mg kg(-1) i.p.+100 mg kg(-1) s.c.). The hyporesponsiveness was also absent in o valbumin sensitized guinea-pigs exposed to an aerosol of ovalbumin 60 min before testing with Ach. 3 In non-sensitized guinea-pigs, pretreat ment with butoxamine (1 mg kg(-1)i.v.) or with theophylline (25 mg kg( -1) i.v.), completely abolished the effect of noise-exposure. In contr ast, pretreatment with L-N-G-nitro-arginine methyl ester (L-NAME, 10 m g kg(-1) i.v.), alpha-chymotrypsin (2 U kg(-1) i.v.) or with enprofyll ine (10 mg kg(-1) i.v.), did not affect it. 4 In conclusion, our exper iments reveal inhibitory mechanisms upon Ach-induced bronchoconstricti on activated by a stress stimulus and this is absent in sensitized ani mals. These mechanisms seem to be linked to the adrenergic beta 2-rece ptors and a role for the purinergic system (via A-receptors) may also be present.