ENDOTHELIUM-DEPENDENT RELAXATIONS OF RAT AORTA TO ACETYLCHOLINE ARE NOT INHIBITED BY PERTUSSIS TOXIN

1 We have investigated the effects of pretreatment with pertussis toxi n (20 mug kg-1, i.v., 3-4 days) on endothelium-dependent relaxations o f rat aorta to acetylcholine (ACh). 2 Pertussis toxin pretreatment fai led to affect the contraction to noradrenaline (NA) (I mum), but signi ficantly reduced the contraction to KCl (40 mm) (vehicle: 0.79 +/- 0.5 9; pertussis toxin treated: 0.63 +/- 0.03 g; P<0.05). 3 Relaxations to ACh in aortic rings contracted with NA were unaffected by pertussis t oxin, but relaxations in tissues contracted by KCl were significantly increased by pertussis toxin pretreatment (maximum relaxation to ACh; vehicle: 21.4 +/- 3. 1 %; pertussis toxin treated: 40.1 +/- 6.5%; P<0. 05). However, relaxations to ACh were also significantly increased by reducing KCl from 40 to 20 mm, thus reducing the size of the contracti on. 4 The nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine r educed relaxations to ACh in both vehicle and pertussis toxin treated tissues contracted with NA or KCl. 5 It is concluded that pertussis to xin pretreatment does not directly influence endothelium-dependent rel axations to ACh in rat aorta, but reduces contractions to KCl. Changes in the contractile response to KCl influenced the degree of relaxatio n to ACh.