Abstract
The effect of intestinal fatty acid perfusions on translocation of the brush-border enzyme, intestinal alkaline phosphatase, was assessed in the rat. Each of two consecutive loops of proximal small bowel were perfused simultaneously in anesthetized rats with three solutions in random order. The solutions consisted of a control solvent solution containing sodium taurocholate, a reference fatty acid solution containing C18 : 1 in taurocholate, and a test solution containing either C18 : 1, C16 : 1, C12 : O, C8 : 0 or C6 : 0 in taurocholate. When fatty acid was present in the perfusate more enzyme was released into the intestinal lumen than by taurocholate alone. Long-chain fatty acids were 3.4 times more effective than medium-chain fatty acids in releasing intestinal alkaline phosphatase (P < 0.001). An exponential relationship was found between fatty acid chain length and release of enzyme. The effect of each fatty acid on the release qf enzyme was similar in the two loops and reversible. Another brush-border enzyme, sucrase, used as a reference enzyme, was also released by the fatty acid perfusions. The amount released was also related to the carbon-chain length of the fatty acid but less sucrase than intestinal alkaline phosphatase was released in response to fatty acid perfusion. Histochemicat studies on the activity of alkaline phosphatase confirmed the outflow of intestinal alkaline phosphatase from the brush border into the bowel lumen. Simultaneously, intestinal alkaline phosphatase also moved in the opposite direction into the mucosal lymphatics. These changes were most pronounced following long-chain fatty acid perfusions, and less apparent after medium-chain fatty acid perfusion. The data demonstrated: (1) a bidirectional flow of brush-border intestinal alkaline phosphatase, and (2) that luminal enzyme activity is exponentially related to the carbon-chain length of the fatty acid being absorbed. The results suggest participation of intestinal alkaline phosphatase in fat absorption.
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