Secretory function of the esophageal mucosa in opossum: the role of cholinergic, peptidergic and histaminergic pathways
Namiot Z, Sarosiek J, McCallum RW

Purpose: Esophageal histology in the opossum reveals numerous submucosal mucous glands closely resembling those commonly found in humans. The aim of the study was to examine the secretion of these glands using the commonest secretagogues.
Material and methods: The esophageal lumen in 5 male opossums was continuously perfused with saline during sixteen consecutive 5 min perfusion periods. After four initial equilibrating periods, each animal was injected (s.c.) with pentagastrin (6 g/kg), bethanechol chloride (100 g/kg) or histamine dihydrochloride (0.5 mg/kg). All sixteen (5 min) perfusates were assayed for protein by Lowry, mucin by PAS and viscosity using a cone/plate digital viscometer. Results were expressed as mean±SE. Statistical analysis was performed using paired Student’s t-test.
Results: Administration of bethanechol resulted in a significant increase in esophageal mucin release from 2.4±0.4 to 8.0±1.2 g/cm2/min (p<0.01); enhancement of protein output from 8.9±2.0 to 20.4±2.9 g/cm2/min (p<0.01) and potentiation of specific viscosity from 7.5±0.6 to 14.4±0.8 (p<0.01). Pentagastrin-induced release of mucin reached the maximal value of 5.5±0.7 g/cm2/min (p<0.01), protein output increased to 20.0±2.7 (p<0.01) and viscosity expanded to 11.7±0.9 (p<0.05). Histamine evoked an increase in mucin release to 3.9±0.4 g/cm2/min (p<0.01), protein output to 24.1±3.3 g/cm2/min (p<0.01) and viscosity to 12.8±1.1 (p<0.05). 
Conclusions: The significant influence of cholinergic, histaminergic and peptidergic stimulation on physical and chemical properties of the esophageal secretion provides evidence for the role of these pathways in the pathophysiology of the esophageal mucosa.

Key words:   esophageal secretion, bethanechol, pentagastrin, histamine.