Characterization of an endothelial 5-hydroxytryptamine (5-HT) receptor mediating relaxation of the porcine coronary artery.

The pharmacological properties of the endothelial 5-hydroxytryptamine (5-HT) receptors involved in relaxation of vascular smooth muscle were determined in rings of pig coronary artery contracted with 10 nmol/l of the thromboxane A2 receptor agonist 9,11-dideoxy-11 alpha,9 alpha-epoxy-methano-prostaglandin F2 alpha (U 46619). (1) In the presence of 10 mumol/l ketanserin, relaxation was obtained with: 5-HT (apparent pD2 value 7.00), 5-carboxamidotryptamine (5-CONH2-T; 6.42), 5-aminotryptamine (5-NH2-T; 5.96), 5-methoxytryptamine (5-OCH3-T; 5.92), tryptamine, 7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo(1,2-a)quinoxaline maleate (CGS 12066 A) and 5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole succinate (RU 24969). The maximum relaxation obtainable with the agonists was about 40-60% of the U 46619-induced contraction and the concentration-response curves for 5-HT, 5-NH2-T and 5-OCH3-T were bell-shaped. The endothelium-dependence of this effect (i.e. the failure to relax the artery in endothelium-denuded preparations) was demonstrated for 5-HT, 5-CONH2-T, RU 24969, CGS 12066A and tryptamine. (2) 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 4-hydroxytryptamine, quipazine and yohimbine were ineffective in decreasing the tension of arteries with or without endothelium. Ipsapirone elicited full relaxation of U 46619-induced contraction, but this effect was not endothelium-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)