5-Hydroxytryptamine potentiates neurogenic contractions of rat isolated urinary bladder through both 5-HT7 and 5-HT2C receptors

Serotonin (5-HT) enhances the neurogenic contractile response induced by electrical field stimulation (EFS) in the rat isolated urinary bladder. The aim of this study was to functionally characterize the receptors involved in this effect by using a range of 5-HT receptor subtype selective agonists and antagonists. 5-HT produced a concentration-dependent potentiation of contractile responses to EFS with a pEC50 value of 6.86 ± 0.24. SB-269970 (0.01, 0.1 and 1 μM), a selective 5-HT7 receptor antagonist, caused a concentration-dependent rightward shift of the 5-HT-induced response. The pA2 value was 8.16 with a slope of 0.46 ± 0.08. Neither ketanserine nor SB-204741, 5-HT2A and 5-HT2B receptors antagonists, respectively, affected the concentration–response curve to 5-HT. However, 5-HT response was antagonized by the selective 5-HT2C receptor antagonist SB-242084 (0.1 and 1 μM). In the presence of 1 μM of both antagonists SB-269970 and SB-242084, 5-HT response was almost fully inhibited. 5-CT, a 5-HT7 receptor agonist, induced a biphasic concentration-dependent potentiation of neurogenic contractions. SB-269970 concentration-dependently antagonized the first phase of 5-CT response with a pA2 value of 8.77 and a slope not significantly different from unity (0.91 ± 0.11) that suggests a competitive antagonism. WAY-161503, a 5-HT2C receptor agonist (0.01–10 μM), induced a concentration-dependent potentiation of contractile response to EFS while DOI (a selective 5-HT2A agonist) had no effect. SB-242084 (0.1 and 1 μM) antagonized the effect of WAY-161503 in a concentration-dependent manner. The current results demonstrate that 5-HT potentiates neurogenic contractions of rat isolated detrusor muscle through both 5-HT7 and 5-HT2c receptors.