MODULATION BY PERTUSSIS TOXIN OF SALBUTAMOL-INDUCED AND ARECOLINE-INDUCED EFFECTS IN THE ISOLATED HEART AND AORTA OF THE RAT

The modulatory effects of pertussis toxin pretreatment on responses me diated via beta-adrenoceptors and muscarinic acetylcholine receptors w ere investigated in isolated rat hearts and aortic rings 4 days after in vivo administration of pertussis toxin. In isolated hearts, pertuss is toxin increased heart weight and baseline coronary flow values but did not effect baseline left ventricular pressure values. In unpaced h earts, pertussis toxin inhibited the arecoline-induced cardiac standst ill, while in paced hearts, the beta(2)-adrenoceptor agonist salbutamo l produced a dose-dependent vasodilatation with similar characteristic s in pertussis toxin and control preparations. Pertussis toxin had no effect on myocardial or aortic cyclic nucleotide levels and the myocar dial beta-adrenoceptor density (B-max) and dissociation constant (K-d) . In precontracted aortic rings, pertussis toxin had no effect on the salbutamol or arecoline induced vasorelaxation. In summary, we demonst rated a reduced cholinergic responsiveness in isolated hearts but an i ntact beta(2)-adrenoceptor pathway in isolated hearts as well as in is olated aortic rings after pertussis toxin pretreatment. In aortic ring s no change in muscarinic acetylcholine receptor responsiveness occurr ed.