Sheep which had been either previously infected with 3. circumcincta or maintained worm-free, were surgically prepared with separated fundic pouches and abomasal
cannulae and subsequently infected with 20,000 O. circumcincta larvae three times weekly. A reduction in food intake and increases in total
acid output from the pouches and plasma
pepsinogen levels were evident in both groups of sheep 4 days after repeated
infections commenced; effects which increased in severity after 12 or more days. Except for a transient period of slight failure, previously infected sheep retained the capacity to acidify their abomasal contents whereas previously worm-free sheep lost this capacity. These changes were reversed between 2 and 7 days
after treatment with
thiabendazole (88 mg.kg-1). Secretory capacity of the fundic pouches was tested with
histamine (40 mug.kg-1), the
histamine antagonist (
burimamide 8 mg.kg-1) and
atropine (100 mug.kg-1).
Ostertagiasis reduced or abolished the stimulatory effects of
histamine. An increase in secretion volume and
acid output was obtained after food was freshly provided, even though as little as 25 gm was consumed.
Atropine and
burimamide both caused a profound decrease in pouch secretion and
acid output. These data are consistent with the hypothesis previously stated that in
ostertagiasis the hypersecretion from fundic pouches is due to increased levels of circulating
gastrin.