A comparison of 5‐hydroxytryptamine receptors mediating contraction in rabbit aorta and dog saphenous vein: evidence for different receptor types obtained by use of selective agonists and antagonists

1 Using recently available selective agonists and antagonists we have examined further our postulate (Apperley et al ., 1980) that 5‐hydroxytryptamine (5‐HT) mediates contraction of dog saphenous vein via a different 5‐HT receptor type from that in the rabbit aorta. 2 In the rabbit isolated aorta, ketanserin and spiperone were potent, specific, competitively‐acting antagonists of the contractile effects of 5‐HT. 3 In contrast, in the dog isolated saphenous vein neither ketanserin nor spiperone caused any rightward displacement of concentration‐response curves to 5‐HT although the maximum response was reduced by about 10%. 4 In the rabbit aorta 5‐carboxamidotryptamine (5‐CONH 2 ‐T) was a weak agonist whilst the 5‐N,N‐dimethyl and 5‐N‐ethyl derivatives were even weaker or inactive. The contractile effect of 5‐CONH 2 ‐T in the rabbit aorta was potently and competitively antagonized by ketanserin. 5 In contrast, in the dog saphenous vein 5‐CONH 2 ‐T and its 5‐N,N‐dimethyl and 5‐N‐ethyl derivatives were all potent agonists. The contractile effect of 5‐CONH 2 ‐T was not markedly affected by ketanserin. 6 The profile of action of ketanserin and spiperone in the rabbit aorta is consistent with the view that 5‐HT 2 receptors mediate contraction in this preparation. However, the 5‐HT receptor mediating contraction in the dog saphenous vein appears to be ‘5‐HT 1 ‐like’, sharing a number of characteristics with the 5‐HT 1 recognition site identified from [ 3 H]‐5‐HT ligand binding studies in brain tissue. tissue.