EFFECTS OF A SERIES OF INFECTIONS OF OSTERTAGIA-CIRCUMCINCTA ON GASTRIC-SECRETION OF SHEEP

Sheep previously infected with O. circumcincta or maintained worm-free were surgically prepared with separated fundic pouches and abomasal cannulae and subsequently infected with 20,000 O. circumcincta larvae 3 times/wk. Reduced food intake and increased total acid output from the pouches and plasma pepsinogen levels were evident in both groups of sheep 4 days after repeated infections commenced; these effects 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; previously worm-free sheep lost this capacity. These changes were reversed 2-7 days after treatment with thiabendazole (88 mg/kg). Secretory capacity of the fundic pouches was tested with histamine (40 .mu.g/kg), the histamine antagonist (burimamide 8 mg/kg) and atropine (100 .mu.g/kg). 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 that in ostertagiasis the hypersecretion from fundic pouches is due to increased levels of circulating gastrin.