Effects of Ostertagia ostertagi on gastrin gene expression and gastrin-related responses in the calf.

1. Infection with the bovine abomasal nematode Ostertagia ostertagi results in a loss of acid-secreting parietal cells and an increase in gastric pH. The effects of an experimental infection on gastrin mRNA expression, blood and tissue gastrin concentrations, the different molecular forms of gastrin in each, and pyloric mucosal chromogranin A-derived peptides were investigated in the calf. 2. An increase in blood gastrin concentrations in the infected group reached a peak by day 28 postinfection (635 pg ml-1; P < 0.01). Gel chromatography analysis of blood samples revealed that the hypergastrinaemia comprised largely gastrin-34 (G-34) in parasitized calves while gastrin-17 (G-17) predominated in control animals. 3. An 11-fold increase in gastrin mRNA expression was recorded in the parasitized animals which was accompanied by a 23.8% reduction in pyloric mucosal gastrin content and an apparent drop of 24.7% in the number of gastrin-producing G cells detected. There was no major change in the relative abundance of G-17 and G-34 in the pyloric mucosa of infected calves. No significant differences in the concentration of pyloric mucosal chromogranin A-derived peptides were recorded between infected and control groups. 4. These data suggest that the hypergastrinaemia seen in parasitized calves results largely from an increase in gastrin synthesis and that depletion of previously stored peptide makes virtually no contribution to elevated blood gastrin concentrations.

Effect of omeprazole treatment on feed intake and blood gastrin and pepsinogen levels in the calf.

Previous work has shown blood gastrin levels to be elevated and appetite depressed in ostertagia-infected calves. A possible relationship between raised blood gastrin values and feed intake was investigated in worm-free animals using the human gastric acid secretion inhibitor, omeprazole. An initial dose-titration experiment established that administration of the drug by intravenous injection at 1.95 mg kg-1 (four times the recommended human dose rate) resulted in a marked (5.2-fold) increase in blood gastrin levels in the calf. Daily administration of omeprazole by intravenous injection at 2 mg kg-1 for four days in a subsequent experiment resulted in a significant depression in feed intake (up to 40.4 per cent) which was accompanied by a significant rise in blood gastrin levels (peak 940 pg ml-1; 6.5-fold increase over control values). It is suggested that such a rise in hormone levels would reduce reticuloruminal and abomasal motility, slow down the passage of ingesta and, in turn, lead to a reduction in appetite.