Pyruvate metabolism and transport in intestinal epithelium

The small intestinal mucosa is known to have a high rate of aerobic glycolysis. The absence of a Pasteur effect in the small intestine is related to this observation. It was questioned whether this is an artefact. The knowledge of the rate-limiting factors of glycolysis is therefore important. The possibility that hexokinase or phosphofructokinase is rate-limiting is discussed. For phosphofructokinase activity, the energy charge is of critical importance. The energy charge in the usual in vitro preparations, such as the everted sac or isolated epithelial cells, is very low. Oxygen availability in vitro might be limited. Therefore the vascularly perfused small intestine was chosen as a model system. It was found that increasing the oxygen availability by the addition of fluorocarbons to the perfusion medium, raised the energy charge up to in vivo values. Under these conditions a clearcut Pasteur effect could be demonstrated.