Effects of nutrients, endogenous secretions, and fasting on in vitro glucose uptake

The effect of luminal nutrients, endogenous secretions, and metabolic balance on the initial velocity of glucose uptake was measured in everted rings of rat intestine. Animals were fed either by total parenteral nutrition (TPN), or into the midjejunum for 7 days, or fasted for 72 h. Luminal feeding resulted in higher midjejunal glucose uptake per milligram of protein, DNA, and centimeter gut length, when compared to fasting or TPN. Kinetic analysis revealed a higher "apparent" Vmax in the luminally fed group, whereas the "apparent" Km was similar in all groups. Diversion of the pancreaticobility secretions did not affect glucose uptake in luminally fed or TPN-fed animals. TPN-fed and fasted animals had similar glucose uptake. Luminal feeding did not have a remote effect on glucose uptake in intestine isolated from the nutrient stream. The results indicate that luminal nutrients maintain carrier-mediated glucose transport after direct contact with the mucosa. Overall metabolic balance and pancreaticobiliary secretions do not affect carrier-mediated glucose transport. The nutrient effect appears to involve an increased number of glucose carriers per cell without a change in carrier affinity for glucose.