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Abstract
The effect of a β-adrenoceptor agonist on pentagastrin- and histamine-stimulated gastric acid secretion was studied in conscious vagotomized gastric fistula dogs. A dose-dependent inhibition was found after pentagastrin stimulation, whereas minor differences were found after histamine stimulation. No major differences between truncal, selective, and parietal cell vagotomy were found after pentagastrin stimulation, whereas one truncal vagotomy dog showed a high inhibition after histamine stimulation. Dose-response experiments with five doses of pentagastrin or histamine (single-dose studies) and two doses of β-agonist suggested a change after vagotomy in the mechanisms of inhibition of gastric acid secretion: for pentagastrin, from a non-competitive type to an uncompetitive type, and for histamine, from a competitive type to a non-significant inhibition. Furthermore, the dose-response curves for the vagotomized dogs were very similar to the curve from intact innervated dogs inhibited by a β-agonist, from an earlier study. These findings may indicate that a decrease in cholinergic tone and an increase in sympathetic tone have identical effects on pentagastrin- and histamine-stimulated gastric acid secretion, and a counterbalance between the two nervous systems on gastric acid secretion is suggested.