In vitro sensitivity of rat esophagus to agonists in different alkaline mediums

An in vitro study was performed to determine the in vitro sensitivity of rat esophagi to contracting and relaxing agonists in different alkaline mediums.

Twenty-four Wistar rats weighing 200 to 250 g were included in the study. After inducing anesthesia with thiopental sodium (50 mg/kg), the rats were killed, and the distal esophagus (DE) and gastroesophageal junction (GEJ) were removed. Excised tissues were suspended under 0.6 g of resting tension in a tissue bath containing 10 mL of Tyrode solution at 37°C. The esophageal segments were divided into 4 groups, each with a different pH medium: 7.4, 7.6, 7.8, and 8. To evaluate the smooth muscle activity of the rat esophagus in different alkaline mediums, cholinergic agonist carbachol (a cholinergic agonosit) and KCl (which acts on calcium channels) were added to the organ baths to obtain concentration-dependent contraction responses. Relaxation responses were obtained using an adrenergic agonist, isoproterenole. Data obtained from different pH mediums were analyzed using Kruskal-Wallis nonparametric analysis of variance and post hoc Dunn's test.

The pH of the medium has no effect on the concentration-dependent contracting responses to carbachol in the DE, but responses obtained in pH 8 medium were significantly lower in the GEJ (P < .05). In pH 8 medium, concentration-dependent relaxation responses to isoproterenole were also significantly lower (P < .05). When contractile responses to KCl were evaluated, the groups with pH 7.6 and 7.8 medium were found to have higher responses in the DE segments than other groups (P < .05). However, the GEJ segments had lower contractile responses to KCl in pH 8 medium (P < .05).

Although different alkaline mediums caused no alteration in esophageal smooth muscle responses to cholinergic stimulation, GEJ responses were lower in pH 8 medium. Relaxation responses, owing to increased adrenergic activity, decreased when the pH of the medium was increased to 8. Calcium-dependent contractions caused by KCl decreased in both segments in pH 8 medium but increased in the DE in pH 7.6 medium.