Studies on the intestinal surface acid microclimate: developmental aspects.

The existence and general characteristics of the intestinal surface acid microclimate (ISAM) in the developing intestine of suckling and weanling rats were examined. ISAM pH measurements were performed in vitro using a sensitive glass pH-microelectrode. The results showed that the ISAM does exist in both suckling and weanling rat intestine. In both suckling and weanling rats, ISAM pH was significantly (p less than 0.01) lower in the jejunum than in the ileum, an observation similar to that previously reported in the small intestine of adult rats. In the colon, however, ISAM pH of suckling rats was significantly (p less than 0.01) lower than that of weanling and adult rats. Studies on the relationship between jejunal ISAM pH of weanling rats and incubation buffer pH showed that the two are not in equilibrium. Jejunal ISAM pH of weanling rats was significantly inhibited by: 1) the mucolytic agent N-acetyl-L-cysteine, 2) stirring of the incubation medium, 3) Na+ removal, 4) glucose removal (or substitution by the unmetabolizable galactose), and 5) metabolic inhibitors (iodoacetate and dinitrophenol). These results demonstrate the existence of the ISAM in the developing intestine of suckling and weanling rats and shows the dependence of the ISAM on Na+, metabolizable substrate(s) and normal intracellular metabolism. Furthermore, surface mucus appears to play a role in maintaining the ISAM, most probably through retaining the H+ at the intestinal surface.