Development changes esophageal smooth muscle reactivity: an in vitro study.

This study was designed to determine if age related changes occur in esophageal smooth muscle reactivity in developing rats. Esophageal smooth muscle strips were obtained from three groups of rats: neonatal (1-3 days old), 1-month-old (30-35 days old) and young adults (4 months old). Esophageal smooth muscle reactivity was assessed in vitro by organ chamber experiments. Concentration-response curves were analyzed for differences in smooth muscle reactivity. Contractile response to cholinergic agonist carbachol increased in the neonatal group with increased maximum contraction compared to the other groups. However, there was no change in pD(2) value among the groups. Maximum contraction evoked by KCl was also significantly increased in the neonatal group compared to the adult group. Relaxation responses elicited by beta adrenoceptor agonist isoproterenol and 5-hydroxytryptamine (5-HT) receptor agonist serotonin were increased in the neonatal group with increased E(max) and pD(2) values compared to the other groups. The present study indicates that the neonatal esophageal smooth muscle responds to serotonergic, adrenergic and cholinergic agonists to a significantly greater degree than the adult esophageal smooth muscle.