Effects of spasmogens on relaxant dose-response curves to full or partial agonists at beta-adrenoceptors of guinea pig isolated trachea.

When guinea pig isolated trachea is contracted with either carbachol or methacholine, relaxant concentration-response curves to isoprenaline, salmefamol and fenoterol were shifted to the right, compared with curves obtained with either spontaneous or histamine-induced tone. Carbachol and methacholine also reduced the maximal relaxation to fenoterol and abolished relaxations to the partial agonist pindolol. It is concluded that the processes linking receptor to contractile response in trachea are different for histamine receptors and muscarinic cholinoceptors.