Contractile responses to tryptamine analogues in isolated smooth muscle

Tryptamine and its benzo[b]thiophene and 1-methylindole analogues had a lower affinity for receptors in rat stomach fundus strips than did serotonin; the interaction between serotonin and methysergide in this system was competitive, while the interactions between tryptamine and its analogues and methysergide were noncompetitive. In contrast, the affinity of tryptamine and 1-methyl-tryptamine for receptors in rat aorta strips was greater than the affinity for serotonin; all three compounds showed noncompetitive interactions with methysergide. The results support the hypothesis of differing serotonin receptors in the two tissues.