The effects induced by the local administration of capsaicin on acid production have been investigated in the continuously perfused stomach of the anesthetized rat. Basal acid secretion was not influenced by 10 min intragastric perfusion with capsaicin (300 micrograms min-1). Acid responses elicited by distension of the stomach with increases in intragastric pressure of 5 and 10 cm H2O were not modified after a 10 min intraluminal infusion with 80 or 300 micrograms min-1 of capsaicin. H+ output stimulated by higher intraluminal pressure (20 cm H2O) were significantly decreased by intraluminal infusion of capsaicin (20, 80, 300 and 600 micrograms min-1). Acid responses to carbachol (4 micrograms kg-1, i.p.) were not influenced by intragastric (300 micrograms min-1), or systemic neonatal, treatment with capsaicin. Intraluminal infusion of the neurotoxin tetrodotoxin (0.12 micrograms min-1, 10 min) decreased acid responses to an increase in intragastric pressure of 20 cm H2O but not those elicited by distention with a pressure of 10 cm H2O. Neonatal systemic treatment (s.c.) with capsaicin or local gastric serosal application of either capsaicin or tetrodotoxin abolished acid responses to gastric distension (+20 cm H2O). Capsaicin (80 micrograms min-1) and tetrodotoxin (0.12 micrograms min-1) infused concurrently into the lumen did not inhibit gastric acid secretion stimulated by an increase of 20 cm H2O in intragastric pressure to any greater extent than did either drug given alone.(ABSTRACT TRUNCATED AT 250 WORDS)