Abstract
1. The pharmacological characterization of the 5-HT3 receptors in guinea-pig isolated tissues is described. The tissues used were ileum (longitudinal muscle-myenteric plexus), colon and vagus nerve. The guinea-pig isolated colon is a novel preparation. 2. In the guinea-pig isolated ileum, 5-hydroxytryptamine (5-HT, 1 x 10(-8)-3 x 10(-5) M) and the selective 5-HT3 receptor agonist 2-methyl-5-HT (3 x 10(-7)-1 x 10(-4) M) caused concentration-related contractions. The 5-HT concentration-response curve was biphasic whilst the 2-methyl-5-HT curve was monophasic. The EC50 value for the low potency portion of the 5-HT curve was 4.1 x 10(-6) M. The EC50 for 2-methyl-5-HT was 1.23 x 10(-5) M. Selective 5-HT3 receptor antagonists caused rightward shifts of the 2-methyl-5-HT curve and the lower potency portion of the 5-HT curve. Neither ketanserin (1 x 10(-6) M) nor methysergide (1 x 10(-5) M) antagonized the responses to 5-HT or 2-methyl-5-HT. 3. In the guinea-pig isolated colon, 5-HT (3 x 10(-7)-3 x 10(-5) M; EC50 2.4 x 10(-6) M) caused contractions which were mimicked by 2-methyl-5-HT (1 x 10(-6)-1 x 10(-4) M; EC50 7.2 x 10(-6) M). Selective 5-HT3 receptor antagonists caused rightward displacements of the 5-HT concentration-response curves.(ABSTRACT TRUNCATED AT 250 WORDS)
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Selected References
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