INFECTION OF SHEEP WITH ADULT AND LARVAL OSTERTAGIA-CIRCUMCINCTA - GASTRIN

Gastric endocrine cell populations and serum and tissue gastrin have b een examined in sheep which were infected either intraruminally by tub e with 150000 Ostertagia circumcincta larvae followed by a trickle inf ection of 10000 larvae thrice weekly for 8 weeks or by the transfer of 15000 adult worms directly into the abomasum and killed 8 days later. Depletion of both antral gastrin and somatostatin was evident in both groups: tissue gastrin concentrations were reduced by 85% in the tric kle infection and both G cells (gastrin-containing) and D cells (somat ostatin-containing) were pale and fewer after adult worm transfer. The concurrent depletion of antral,gastrin and somatostatin supports the contention that the hypergastrinaemia in parasitised sheep is largely secondary to the increase in abomasal pH. Although there was no change in the proportions of G34 and G17 in the tissues, there was an increa se in the longer form of gastrin in the circulation of the larval-infe cted sheep, suggesting that there may be differential secretion of G17 and G34 which may be exaggerated as the rate of secretion increases. Although the fundic mucose was thicker following trickle infection, th ere was no evidence of enterochromaffin-like cell hyperplasia in eithe r infected group. It is suggested that hypergastrinaemia may be benefi cial to the host, as it may allow the abomasum to regain the ability t o acidify its contents during continued exposure to the parasites. (C) 1998 Australian Society for Parasitology. Published by Elsevier Scien ce Ltd. All rights reserved.