CHANGES IN DUODENAL CONTRACTILITY INDUCED BY CALCIUM-ANTAGONISTS WITH DIFFERENT MODES OF ACTION

1. The inhibitory action of nifedipine, verapamil, diltiazem and trifluoperazine has been examined on isolated duodenum from rats and rabbits. 2. On rabbit duodenum Ca2+ antagonists caused a reduction of the spontaneous motility in very low concentrations (10-12-10-6 M). 3. On rat duodenum Ca2+ antagonists inhibited the contractile response to BaCl2, CaCl2 and to field stimulation, nifedipine being the most potent compound (threshold concentration down to 10-12 M). 4. The above results indicated that Ca2+ antagonists can markedly alter the duodenal motility, both basal and drug-stimulated. 5. The high potency of nifedipine and the selective antagonist by Bay K 8644 against nifedipine suggest the presence of a specific receptor for the dihydropyridines (DHP receptor) in the duodenum.