In vivo and in vitro effects of muscarinic receptor antagonists on contractions and release of [3H]acetylcholine in the rabbit urinary bladder.
The functional effects of muscarinic receptor antagonists were examined in vivo and in vitro on the rabbit urinary bladder. Inhibitory effects on carbachol-evoked contractions of detrusor strips were pronounced for 4-diphenylacetoxy-N-methylpiperidine (4-DAMP; -logIC50: 8.64), p-fluoro-hexahydro-sila-diphenidol (pFHHSiD; 7.84) and atropine (8.27), while they were less pronounced for pirenzepine (6.62) and methoctramine (5.36). 4-DAMP and methoctramine increased 3H overflow from [3H]choline-labelled strips in response to electrical stimulation, contrary to pirenzepine, which decreased the overflow. Concomitant contractions were markedly reduced by 4-DAMP and by pirenzepine, but not by methoctramine. The -logIC50 estimations for atropine-sensitive electrically evoked contractions revealed methoctramine (4.85) to be less potent on nerve-evoked contractions than on carbachol-evoked contractions, in contrast to pirenzepine (7.15) and 4-DAMP (9.15). The effects of the antagonists in anaesthetized rabbits resembled those in vitro. Thus, muscarinic receptors in the rabbit urinary bladder are heterogeneous; prejunctional facilitatory (M1) and inhibitory (M2) for acetylcholine release, and postjunctional muscarinic M3 receptors mediating contractile responses.
Tobin
G
G
Department of Pharmacology, University of Göteborg, Sweden.
Sjögren
C
C
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D005260:Female; D005703:Gallamine Triethiodide / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D010276:Parasympatholytics / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology*; D010890:Pirenzepine / Q000494:pharmacology; D011817:Rabbits; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000502:physiology; D014316:Tritium; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology* / Q000648:ultrastructure
D003959:Diamines; D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D010880:Piperidines; D011976:Receptors, Muscarinic; D014316:Tritium; C058297:4-fluorohexahydrosiladifenidol; D010890:Pirenzepine; D002217:Carbachol; D000109:Acetylcholine; C054938:methoctramine; D005703:Gallamine Triethiodide