Consumption of O2 by the intestinal mucosa as a function of the concentration of sugars in the medium

Abstract

Preparations of mucosa of rat jejunum, in an oxygen atmospohere (Krebs-Ringer-phosphate. Warburg-method) present va­lues of QO2 between 4.4 and 8.8, according to the animals.

The addition of glucose or fructose to the medium between 0.17 mM and 22.22 mM gives rise to a marked increase, in the oxygen uptake growing at the beginning with the concentration of sugar but reaching maximuns starting from 2.77 mM (glu­cose) and 5.55 mM (fructose). With glucose the maximun in­crease is approximately 95 %, while with fructose it is about 50 %.

With galactose, arabinose and 3-oxymethyl-glucose there are no significant variations in the oxygen uptake. The addition of succinate to the medium, through concentrations of sugar corresponding to saturation of the oxygen consumption, is accompanied by ncw increases in this consumption. The saturation is attributed to some limiting metabolic factor and not to limitation in the entry of the sugar.

The respiratory quotients also increase in the presence of glucose or fructose and are not significantly modified with the other sugars. The active transport of sugars does not require an increase in oxygen uptake of the mucosa, or at least such an increase is not higher than 7 % (sensitivity limit of the method used), and the energy for the said transport can be derived from the sources which can normally be used by the cell, even with respiratory quotients near 0,7.