NO EFFECT OF PERTUSSIS TOXIN ON PERIPHERAL PREJUNCTIONAL ALPHA-2-ADRENOCEPTOR-MEDIATED RESPONSES AND ON ENDOTHELIUM-DEPENDENT RELAXATIONS IN THE RAT

We have investigated the effects of pertussis toxin treatment on a variety of peripheral tissues in the rat. Incubation with pertussis toxin (1 μg ml-1) in vitro failed to alter the negative inotropic actions of acetylcholine in rat left atria. Pretreatment with pertussis toxin (6 μg kg-1, i.v., 3-4 days) abolished the negative inotropic actions of acetylcholine in rat left atria. Pretreatment with pertussis toxin (40 μg kg-1, i.v., 3-4 days) failed to alter the prejunctional inhibitory actions of the α2-adrenoceptor agonist xylazine, either in terms of the isometric contraction to a single stimulus in rat vas deferens or in terms of stimulation-evoked overflow of tritium in atria pre-incubated with [3H]-noradrenaline. Pretreatment with pertussis toxin (6 μg kg-1, i.v., 3-4 days) failed to affect, and pertussis toxin (40 μg kg-1, i.v., 3-4 days) potentiated endothelium-dependent relaxations of rat aorta to histamine and acetylcholine. It seems unlikely that peripheral prejunctional actions of α2-adrenoceptor agonists or endothelium-dependent relaxations of rat aorta involve pertussis toxin-sensitive G proteins.