Capsaicin pretreatment reduces the gastric acid secretion elicited by histamine but does not affect the responses to carbachol and pentagastrin.

Gastric acid secretion was studied following stimulation with a subcutaneous injection of histamine (0.1, 0.5 or 5 mg/kg), carbachol (4, 40 or 160 micrograms/kg) or pentagastrin (25 or 250 micrograms/kg) in conscious rats pretreated with either capsaicin or the vehicle. The secretory response to histamine (0.5 or 5 mg/kg) was greatly reduced in the capsaicin-treated rats, while the slight effect of 0.1 mg/kg histamine and the increase of secretion in response to carbachol and pentagastrin were not affected. The basal secretion was also normal in the capsaicin-treated rats. It is suggested that unlike the effects of carbachol and pentagastrin, the increase of acid secretion elicited by histamine involves a capsaicin-sensitive mechanism. Since capsaicin is a specific neurotoxin for the peptide-containing primary sensory neurons, the present results may indicate that the neurons contribute essentially to the effect of histamine on gastric acid secretion.