Evidence for a parasite-mediated inhibition of abomasal acid secretion in sheep infected with Ostertagia leptospicularis

The acid secretory capacity of the abomasal mucosa was studied in sheep exp erimentally infected with Ostertagia leptospicularis. The acidity of the ab omasal contents, permanently recorded by a pH probe located inside the abom asum, decreased markedly to mean levels between pH 5 and 6. Subcutaneous ad ministration of histamine or carbachol successfully stimulated acid secreti on (pH 3.4). The results indicate that the abomasal mucosa harboured a popu lation of functional parietal cells which were also identified immunohistoc hemically (H+/K-=-ATPase). Ultrastructural investigation before stimulation revealed that the majority of these cells was in a resting state. Despite high serum gastrin levels, the acid secretion was blocked either at the lev el of the parietal cell or the enterochromaffin-like cell by an unknown fac tor, possibly mediated by the parasites. This is the first report of a pari etal cell dysfunction associated with a nematode infection in the abomasum. It is suggested that the parasites induce changes in their environment whi ch favour their survival and/or- increase their reproduction. (C) 2000 Harc ourt Publishers Ltd.