Abstract
The influence of serotonin (5-hydroxytryptamine, 5-HT) on human ureteral smooth muscle was explored in a series of in vitro experiments. 5-HT evoked a dose-dependent contraction of the ureter. The effect of 5-HT was unaltered by blockade of 5HT3 and 5HT4 receptors and muscarinic cholinergic receptors. The 5HT2 receptor antagonist ketanserin (KT; 10––5–10––4M) and mixed 5HT1/5HT2 receptor antagonist methysergide (MS; 5 × 10––5M) inhibited the effect of 5-HT. Since the antagonist dissociation constant at 5HT2 receptors for both KT and MS is found to be approximately 10––9M, it is concluded that this contractile effect may have been mediated by some other, as yet uncharac-terized 5-HT receptor. We believe that 5-HT is a potential neurotransmitter in the human upper ureteral smooth muscle.