Comparison of affinities of muscarinic antagonists to pre- and postjunctional receptors in the guinea-pig ileum.
The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum was preincubated with [3H]choline, then superfused and stimulated electrically (1 Hz 120 pulses). Oxotremorine reduced the evoked outflow of [3H]acetylcholine in a concentration-dependent manner. Each of the six antagonists (scopolamine, methylatropine, trihexyphenidyl, 4-DAMP, clozapine, pirenzipine) produced parallel shifts of the concentration-response curves for the prejunctional effects of oxotremorine. Similarly, in contraction experiments, the antagonists competitively antagonized the postjunctional responses to oxotremorine. The pre- and postjunctional pA2 values did not differ significantly for any of the antagonists. It is concluded that pre- and postjunctional muscarinic receptors in the guinea-pig ileum are pharmacologically similar.
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology; D002794:Choline / Q000378:metabolism; D004558:Electric Stimulation; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009451:Neuroeffector Junction / Q000187:drug effects* / Q000378:metabolism; D010095:Oxotremorine / Q000494:pharmacology; D010276:Parasympatholytics / Q000494:pharmacology*; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism
D001286:Atropine Derivatives; D010276:Parasympatholytics; D011976:Receptors, Muscarinic; D010095:Oxotremorine; C006649:methylatropine; D002794:Choline; D000109:Acetylcholine