INFECTION OF SHEEP WITH ADULT AND LARVAL OSTERTAGIA-CIRCUMCINCTA - EFFECTS ON ABOMASAL PH AND SERUM GASTRIN AND PEPSINOGEN

Infection of sheep with adult or larval O. circumcincta increased seru m pepsinogen and gastrin and abomasal pH. The upper limits of the norm al range, calculated from over 1000 samples collected from parasite-na ive sheep, were set at 2 standard deviations above the mean; these wer e for serum pepsinogen, 454 mU tyrosine l(-1). serum gastrin, 64 pM an d abomasal pH, 3.26. Five infection regimes were used: sheep previousl y exposed to field parasitism were infected with 30,000 larvae intraru minally (Group A), while parasite-naive sheep were administered either 50,000 larvae intraruminally (Group B), 150,000 larvae intraruminally followed by a trickle infection of 10,000 larvae thrice weekly from d ays 21 to 45 (Group C), 150,000 exsheathed larvae via an abomasal cann ula (Group D) or 15,000 adult worms via an abomasal cannula (Group E). Whereas the presence of adult worms rapidly increased serum pepsinoge n (after 8 h) and abomasal pH and serum gastrin (after about 19 h), th e early infective larval stages, regardless of the infection regime, h ad minimal effects until the abrupt rise in all parameters 5-6 days af ter infection. Abomasal pH returned to near normal levels when the inf ections became patent and was not re-elevated by a subsequent trickle infection, whereas serum gastrin and pepsinogen remained high. The ini tial hypergastrinaemia was coincident with the increased abomasal pH, but was preceded by the increase in serum pepsinogen. In several sheep , serum pepsinogen increased very little during the parasitism, althou gh there were typical effects on abomasal pH and serum gastrin. Serum gastrin was depressed when the abomasal pH exceeded about 5.5. It is s uggested that an inhibitor of gastrin release is generated by prolifer ating abomasal microbes under these conditions and that this is a limi tation to the use of elevated serum gastrin in the diagnosis of parasi tism in individual sheep. Copyright (C) 1996 Australian Society for Pa rasitology. Published by Elsevier Science Ltd.