Effects of the muscarinic receptor agonist carbachol and/or antagonist pirenzepine on gastric mucus secretion in rats.

The effects of the muscarinic agonist carbachol on the secretion and accumulation of gastric mucus glycoprotein (mucin) were examined. Gastric mucin obtained from the soluble mucus, adherent mucus gel, and surface mucosal and deep mucosal layer was isolated and quantified. One hour after the subcutaneous administration of carbachol (0.08-80 micrograms/kg body weight) the deep corpus mucin content had decreased significantly (75% of control), corresponding to an increase (120% of control) in the soluble mucin content with 0.8 microgram/kg of carbachol treatment. These changes were counteracted by 10 mg/kg of pirenzepine (selective M1 antagonist) pretreatment. On a single administration of 10 mg/kg of pirenzepine, deep corpus mucin tended to increase, and soluble mucin decreased significantly (49% of the control). These two drugs failed to cause any significant change in the mucin content of the surface and antral deep mucosa or the adherent mucus gel. The muscarinic agonist and the M1 antagonist are thus shown to accelerate the secretion and accumulation, respectively, of mucin in the deep corpus mucosa. Thus intrinsic M1 receptor may possibly be involved in the secretion of mucin in the gastric deep corpus mucosa.