Regional differences in the effect of bile salts on absorption by rat small intestine in vivo.

1. The hypothesis that endogenous bile salts influence water absorption in rat small intestine was tested in vivo. 2. Net water transport was measured under steady-state conditions during single-pass infusion of segments from three regions of the small intestine. Each segment served as its own control. 3. Delipidated rat bile, and solutions of the principal bile salts of the rat, taurocholate and glycocholate, reduced absorption in the proximal jejunum but not in the distal ileum. 4. 1-Palmitoyl,2-oleoyl lecithin, an important biliary lecithin, counteracted the inhibitory effect of taurocholate and of glycocholate on absorption. The presence of biliary lecithins probably explains why whole rat bile did not depress water absorption in the proximal jejunum. 5. Net water transport in the distal jejunum was inversely related to log10 (taurocholate concentration). 6. Endogenous bile salts may help to maintain the fluidity of the contents of the mid-small intestine in the rat after biliary and dietary lecithins have been absorbed.