Affiliation:
1. Department of Pharmacology & Therapeutics, University of Ibadan, Ibadan, Nigeria
Abstract
Abstract
The interaction between the muscarinic receptor agonists, carbachol, acetylcholine (ACh) and methacholine, and antagonists, atropine, gallamine, 4-DAMP and pirenzepine, was studied on the rat isolated rectum preparation. ACh (1.93 times 10−8-1.95 times 10−6M), methacholine (8.7 times 10−8-1.1 times 10−6 M) and carbachol (1.1 times 10−7-3.5 times 10−6 M) induced contractions that were reversibly antagonized by atropine (1.9 times 10−9-4.8 times 10−8 M), 4-DAMP (1.5 times 10−8-2.86 times 10−7 M) gallamine (1.12 times 10−6-1.12 times 10−4 M) and pirenzepine (2.8 times 10−7-7.0 times 10−6 M). The pA2 values were atropine: 8.99 ± 0.28, 9.29 ± 0.14 and 8.86 ± 0.05; 4-DAMP: 8.39 ± 0.10, 8.66 ± 0.15 and 8.26 ± 0.30, gallamine: 5.85 ± 0.23, 5.73 ± 0.25 and 5.96 ± 0.10 and pirenzepine: 6.85 ± 0.44, 7.17 ± 0.13 and 7.21 ± 0.03 against ACh, methacholine and carbachol, respectively. The experimental dose-ratio (atropine + gallamine) was greater than the expected dose-ratio (as predicted by the Paton & Rang rule) for ACh and methacholine while the experimental dose-ratio closely approximates the expected dose-ratio for carbachol. It is suggested that atropine, 4-DAMP pirenzepine and gallamine act on the same receptors but gallamine allosterically altered the binding of the agonists and antagonists to varying extents.
Publisher
Oxford University Press (OUP)
Subject
Pharmaceutical Science,Pharmacology
Cited by
5 articles.
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