The Involvement of the Serotonergic Transmission System in Neonatal and Adult Rat Ileum Contractility Varies with Age

The relevance of age on serotonergic involvement in the control of alimentary contractility has not been pharmacologically described. Experiments were performed to investigate the effects of acetylcholine, atropine, 5-hydroxytryptamine (5-HT) and its related drugs on intestinal segments taken from the neonatal and adult ileum. 5-HT induced concentration-dependent contractions of ileum irrespective of age; however, these contractions were diminished by pretreatment with atropine only in neonatal tissues. In tissues taken from both the neonatal and adult ileum, methysergide (5-HT1/2/5–7 receptor antagonist), ritanserin (5-HT2 receptor antagonist), and RS23597-190/SB204070 (5-HT4 receptor antagonists) all differentially reduced 5-HT-induced contractions at a concentration <100 µmol/l. At higher concentrations, the contractions were comparable to those in control tissues. Granisetron and ondansetron (5-HT3 receptor antagonists) significantly reduced contractions induced by 5-HT at concentrations >30 µmol/l in both neonatal and adult ileum. Combined treatments with ritanserin, granisetron, plus RS23597-190 reduced or abolished contraction responses induced in neonatal ileum by 5-HT. SB269970A (5-HT7 receptor antagonist) and WAY100635 (5-HT1A receptor antagonist) failed to influence contractile responses induced by 5-HT or 5-HT receptor agonists. Pretreatments with WAY100635 and SB267790A also had no influence on the contractile responses induced by 5-HT1A/7 receptor agonist, 5-CT, and 5-HT1A receptor agonist, 8-OH-DPAT, which itself failed to induce a measurable response. It is concluded that the 5-HT-induced contractions in segments taken from both the neonatal and adult rat ileum were mediated via 5-HT2 receptors, 5-HT3 receptors and 5-HT4 receptors. However, the effect of atropine on the neonatal rat intestine indicates that the mechanism of serotonergic involvement in ileal contractility is influenced by age.