Effect of systemic pH on models of altered ileal transport in the rat.

Decreases in arterial pH markedly increase sodium, chloride, and water absorption in the normal ileum and can reverse ongoing cholera toxin-induced secretion. In the current study we examined whether these effects of pH are evident in other models of ileal secretion, and in a model of increased absorption. Rats were anesthetized and transport was measured in ileal loops during respiratory acidosis and alkalosis. Decreases in arterial pH increased absorption equally in control loops and in adjacent loops perfused with a Ringer's solution containing ST toxin (cyclic guanosine monophosphate-mediated secretion), hypertonic mannitol (passive, osmotically mediated secretion), or glucose. Decreases in arterial pH increased absorption in a similar way in loops exposed to cholera toxin (cyclic adenosine monophosphate-mediated secretion) that were then perfused with glucose-Ringer's solution. Alterations in arterial and luminal pH did not affect glucose absorption. These results suggest that the effect of arterial pH on ileal absorption occurs by a mechanism that is independent of these various means of altering transport.