Transport of vitamin A in vitro across normal isolated rat intestine and intestine subjected to ‘partial’ resection

Abstract

The transport of vitamin A across normal and resected intestine was studied in vitro by the method of Darlington and Quastel. The results showed that under aerobic conditions the rate of transport of vitamin A across normal and resected intestine was identical. In contrast, under anaerobic conditions transport was reduced 50% for resected intestine and totally inhibited for control intestine. These results were duplicated under aerobic conditions when 2, 4, dinitrophenol was added to the mucosal solution. Thus for the control intestine, transport is entirely dependent on DNP-sensitive phosphorylation mechanisms which require a wetting agent (polyoxyethylene sorbitan monooleate, ‘Tween 80’) as a solubilizer on the serosal side for the transport of vitamin A across the intestine. The DNP-insensitive mechanisms responsible for 50% of the total transport across the resected intestine were inhibited by iodoacetic acid and sodium fluoride. Chromatographic analysis of intestinal homogenates and mucosal solution at the end of the perfusion demonstrated that vitamin A palmitate is converted to the alcohol either in the lumen or on the surface of the epithelial cells and is then re-esterified in the intestinal mucosa. Transport of this vitamin is via ‘active’ energy-requiring mechanisms. In the normal intestine energy is supplied by oxidative phosphorylation, and in the resected intestine by oxidative as well as anaerobic glycolytic phosphorylation.