The effect of sodium deoxycholate and other surfactants on the mucosal surface pH in proximal jejunum or rat

The mucosal surface pH (acid microclimate) and nucleotide levels of rat proximal jejunum were measured in vivo under various conditions which included exposure to pharmacological agents and to surfactants. Mucosal surface pH was unaffected by sodium nitroprusside, A23187 and amiloride, as was mucosal cGMP content, although amiloride and A23187 reduced cAMP content. In contrast, surfactants elevated the pH of the mucosal surface significantly (P less than 0.001): control value 6.23 +/- 0.02 (n = 12); Lubrol PX 0.8% (v/v) 6.98 +/- 0.02 (n = 5); sodium deoxycholate 2 mmol/l 6.67 +/- 0.04 (n = 5); Triton X-100 0.5% (v/v) 7.41 +/- 0.03 (n = 5). No significant changes in cGMP levels were noted after surfactant treatment, although DOC and Triton X-100 reduced cAMP levels. The ability of higher concentrations of surfactant to elevate the mucosal surface pH beyond neutrality to values similar to plasma pH contrasts with the action of Escherichia coli heat-stable (STa) enterotoxin which at high concentrations could not elevate the mucosal surface pH beyond neutrality. Consistent with the known effects on tight junction permeability, surfactants may act by allowing plasma-like subepithelial fluid to neutralise the microclimate.