Effects of caffeine on transport, metabolism and ultrastructure of isolated rat colon.

The effect of caffeine on the transport, metabolism and ultrastructure of the colon were determined. Segments of proximal colon were excised from the anesthetized rat and prepared for radioisotopic tracing of ion transport in the flux chambers or oxidative metabolism in an incubator. Other segments were fixed before or after caffeine administration for electron microscopy. The isolated rat colon actively transported both Na+ and Cl- in the absorptive direction, mucosa to serosa. Serosal addition of 10 mmol/l caffeine abolished the smaller Na+ transport but did not significantly affect the larger Cl- transport. The electrical potential difference and the short-circuit current rose accordingly. Although the oxidation of glucose was inhibited by 35%, caffeine had no significant effect on the oxidation of the fatty acid, butyric acid. Comparable metabolic responses were obtained using the isolated terminal ileum of the rat. Neither the height nor the density of the microvilli in the proximal colon were affected significantly by caffeine. It may be concluded that caffeine, unlike theophylline, effectively preserves the normal absorptive condition of the colon. Thus, caffeine may have actions other than inhibition of phosphodiesterase in the distal intestine.