Transport and metabolism of glucose by rat small intestine

Abstract

Glucose transport and metabolism by rat small intestine was investigated by using a preparation for the combined perfusion of the lumen and the vascular bed. 2. When 5 mM-glucose was present in the lumen, only 29% was transported unchanged to the vascular side. Lactate output into the vascular and luminal fluids accounted for a further 53% and 4% respectively of the glucose taken up from the lumen. 3. Glucose was readily taken up when added at 5 mM to the vascular compartment only. Vascular lactate output accounted for approx. 33% of the glucose uptake, and luminal lactate for 6%. 4. When 2 mM-glucose was added to the lumen with 5 mM-glucose in the vascular perfusate, there was no detectable net transport of glucose to the vascular side. However, of the glucose taken up from the lumen, 31% and 2% could be accounted for by increases in vascular and luminal lactate respectively. 5. When 10 mM-glucose was added to the lumen, with 5 mM-glucose in the vascular perfusate, 33% of the glucose disappearing from the lumen was transported to the vascular side. Extra lactate output to the vascular and lumen perfusates accounted for 50% and 9% respectively of the glucose uptake from the lumen. 6. These studies indicate that at low luminal glucose concentrations no sugar is transferred to the blood unchanged, and at sugar concentrations of 5--10 mM only 25--50% of the glucose leaving the lumen reaches the serosal side intact. Furthermore, the small intestine has a greater propensity to form lactate from luminal glucose than from vascular glucose.

The glucose paradox. Is glucose a substrate for liver metabolism?

“…Although the nature of the three carbon intermediate has not been firmly identified, lactate (and possibly alanine) would seem to be a likely candidate since it is produced during glucose absorption from the gut (Boyd et al [2]; Nicholls et al [64]) and by muscle and erythrocytes.6 Implicit in this formulation is that carbon flow from the C3 level to glucose-6P must remain active for at least several hours after carbohydrate ingestion, but that the glucose-6P formed is now diverted away from the glucose6Pase reaction and into the pathway of glycogen synthesis. The mechanism of this crucial metabolic switch remains to be delineated.…”

The Effect of Fasting on Rat Portal Venous and Aortic Blood Glucose, Lactate, Alanine, and Glutamine

“…This in vivo finding in a unanesthetized rat is consistant with data of Windmueller and Spaeth (3) who used an anesthetized in situ intestinal preparation. In contrast, Nicholls et al (2) using a perfused intestinal model measured a significant amount of lactate production. Hanson and Parsons (I) determined that the amount of intestinal lactate production in a perfused model was dependent on the hematocrit of the perfusate.…”

Rat splanchnic net oxygen consumption, energy implications.

“…The importance of the intestine as oxygen consumer stems from its function; despite its relatively small size with respect to body weight (Remesar, Arola, Palou & Alemany, 1981) has a very active metabolism, especially in its outermost epithelial strata, since these are cells with a short life and extremely active metabolism (Dickens & Weil-Malherbe, 1941). The intestine plays a significant role in the control of glucose and gluconeogenic precursor output (Remesy, Demigne & Aufrere, 1978;Nicholls, Leese & Bronk, 1983), as well as in amino acid metabolism (Remesy et al 1978;Aikawa, Matsutaka, Yamamoto, Okuda, Ishikawa, Kawano & Masumura, 1973) and fat resynthesis (Bisgaier & Glickman, 1983). Thus it can be expected that its residual energy output would be considerable and its oxygen consumption very high.…”