A continuous dietary supply of free calcium formate negatively affects parietal cell population and gastric RNA expression for H+/K+-ATPase in weaning pigs

Baby formula acidification is a tool to reduce diarrhea. Calcium formate is a dietary acidifier frequently used in animal weaning diets and a source of available calcium. Gastric acidification reduces gastrin release and hydrochloric acid secretion. To study the medium-term effects on fundic gastric mucosa we set up a feeding experiment in a pig-weaning model. In weaning pigs fed a diet supplemented with free or fat-protected calcium formate, we evaluated 1) the number of hydrochloric acid-secreting parietal cells, by immunohistochemistry using an antibody against H+/K+-ATPase; 2) the number of entero-endocrine cells immunohistochemically stained with chromogranin A (CGA), somatostatin and histamine and 3) the expression of the H+/K+-ATPase gene, by Real Time RT-PCR in the oxyntic mucosa. Cells co-staining for CGA and histamine were defined as enterochromaffin-like (ECL) cells. Pigs fed calcium formate had less parietal cells and a lower expression of the H+/K+-ATPase gene as compared to the controls (P < 0.05). This reduction was not observed with fat-protected formate supplementation. Somatostatin immune-reactive cells were also more numerous with free formate addition (P < 0.05). The number of ECL cells was not affected. Using covariance analysis, the number of parietal cells explained part of the expression of H+/K+-ATPase gene (positive correlation, r=0.385, P < 0.01), and excluded the statistical significance of the diet. Effects on the oxyntic mucosa should be checked when a diet supplemented with calcium formate is discontinued. Furthermore, a reduction of the number of parietal cells could impair the absorption of vitamin B12 due to a reduced secretion of the intrinsic factor by these cells.