5-Hydroxytryptamine receptor profile in healthy and diseased human epicardial coronary arteries

The aim of the study was to investigate the receptor events that mediate the vascular effects of 5-hydroxytryptamine (5-HT) on human coronary arteries, since 5-HT has long been thought to play a role in coronary artery vasospasm.

Recently available selective receptor agonists and antagonists were used to examine the 5-HT receptor subtypes present in human epicardial coronary arteries using in vitro organ baths.

138 segments of coronary arteries were obtained from 21 patients aged 2-66 years undergoing heart transplantation.

5-HT produced only concentration dependent contractions of coronary artery segments. No evidence was obtained for 5-HT receptors mediating either endothelium dependent or endothelium independent vasorelaxation. In tissue from patients without ischaemic heart disease, 5-HT effects were mimicked by (+/-)-alpha-methyl-5-HT (alpha-me-5-HT), a selective agonist at 5-HT2 receptors. In addition, the selective 5-HT1-like receptor agonist GR43175 produced contractions which achieved 30% of the maximum response to 5-HT. Responses to alpha-me-5-HT were surmountably antagonised by the non-selective antagonist methiothepin (0.1 mumol.litre-1) as well as the 5-HT2 receptor antagonist ketanserin (0.1 mumol.litre-1). In contrast GR43175 effects were resistant to blockade by ketanserin, but remained sensitive to methiothepin. Responses to the two agonists were not antagonised by the 5-HT3 receptor antagonist MDL72222 (1.0 mumol.litre-1). Vessel segments from ischaemic heart disease patients also contracted to alpha-me-5-HT and GR43175. Diseased arteries contracted with a decrease in the maximal response induced by both alpha-me-5-HT and by 90 mM K+ depolarisation compared to "normal" vessels, but the effect of GR43175 was preserved in the diseased arteries. Vascular rings adjacent to an atheromatous lesion were more reactive to GR43175 than serial segments taken distal to the lesion.

These results show that both 5-HT1-like and 5-HT2 receptors mediate contraction of human epicardial coronary arteries and indicate that effects mediated by 5-HT1-like receptors but not 5-HT2 receptors are preserved in patients with ischaemic heart disease.