Evidence for a 5-HT1-like receptor mediating the amplifying action of 5-HT in the rabbit ear artery. |
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| Authors: | I. S. de la Lande |
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| Affiliation: | Department of Clinical and Experimental Pharmacology, University of Adelaide, South Australia. |
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| Abstract: | 1. The nature of the 5-hydroxytryptamine (5-HT) receptors which amplify the vasoconstrictor effect of methoxamine was examined in the rabbit isolated perfused ear artery with intact endothelium. Indices of amplification were leftward shifts of methoxamine dose-response (DR) curves produced by 5-HT (0.3 microM) (Method I), and the appearance of vasoconstrictor responses to 5-HT receptor agonists when methoxamine was present in a near-threshold concentration (Method II). 2. The amplifying effect of 5-HT (Method I) was unaffected by prazosin (0.08 microM), was partly depressed by 5-HT2-receptor antagonists in high concentrations (ketanserin 0.5 microM, LY53857, 1.0 microM), and was abolished by a non-selective antagonist of 5-HT1 and 5-HT2 receptors (methiothepin, 0.01 microM). 3. Amplifying potencies of agonists assessed by both Methods I and II were in the order 5-carbox-amidotryptamine (5-CT) greater than 5-HT greater than alpha-methyl 5-HT. The potency of sumatriptan (assessed by Method II only) was intermediate between those of 5-HT and alpha-methyl 5-HT. 4. Ketanserin and LY53857 inhibited the amplifying action of 5-CT to about the same extent as that of 5-HT. 5. The amplifying potencies of the agonists are in marked contrast to the reported contractile potencies in the rabbit aorta where the receptor is 5-HT2, but are almost identical with reported contractile potencies in the dog saphenous vein where the receptor is 5-HT1-like.(ABSTRACT TRUNCATED AT 250 WORDS) |
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