Retinol lymphatic and portal transport: influence of pH, bile, and fatty acids.

Absorption of [3H]retinol into lymph and bile was studied in unanesthetized rats with cannulated thoracic and common bile ducts. Retinol in a micellar solution was infused into the duodenum. Absorption of retinol into lymph increased when the infusate's taurocholate concentration was increased to 10 mM, when the hydrogen ion concentration was increased, or when octanoic acid was added to the infusate. Absorption of retinol into lymph decreased when the taurocholate concentration was decreased to 5 mM or when long-chain unsaturated fatty acids or retinoic acid were added to the duodenal infusate. Retinol absorption into bile increased following additions of linoleic and arachidonic acids to the infusate, but absorption did not change following modifications of the infusate's taurocholate concentration or pH. These experiments, which demonstrate that intraluminal factors do modify the extrusion of retinol into bile and lymph, enhance our overall understanding of the process of absorption of this lipid nutrient.