Absorption of sugars in vitro by the intestine of the golden hamster.

As early aa 1900, Hedon (1) demonstrated that isotonic solutions of glucose and galactose were absorbed more rapidly than similar solutions of arabinose, an observation suggesting selective absorption of certain hexoses. This observation has been amply confirmed and at least two general groups of sugars delineated, one group of rapidly absorbed sugars (glucose and galactose) and another more slowly absorbed (mannose, sorbose, xylose, arabinose, and all disaccharides), with fructose intermediate betwken the two (24). The absorption of the first group is inhibited by the poisons iodoacetate (4) and phlorizin (5, S), while that of the latter is unaffected. Furthermore, the absorption of glucose, galactose, and fructose (but not of other sugars) is associated with an accumulation of organic phosphates within the intestinal mucosa (7-9). On the basis of this and other evidence, it is generally accepted that only glucose, galactose, and fructose are absorbed by mechanisms mediat,ed by enzyme reactions (probably phosphorylation and dephosphorylation) (4) and requiring the expenditure of energy. Recently, however, a number of observations have complicated this generalization. Hele (10, 11) has shown that mannose and xylose are also phosphorylated by the intestinal mucosa; the rate of phosphorylation of these sugars in vitro parallels the rate of their absorption in tivo. Naito (12) has shown rapid absorption of ribose compared with other pentoses and accumulations of phosphate esters in the mucosa during its absorption. He concluded that ribose is phosphorylated and that it is absorbed by an active process. Kjerulf-Jensen (13) concluded that the fructose-l-phosphate which he isolated from intestines absorbing fructose was probably an intermediate not only in glucose formation but also in the active transport of fructose, as such, across the epithelium of t,he intestine. It seemed desirable to reinvestigate the behavior of various sugars with one of the recently developed in vitro techniques (14). Two criteria for active transport may be tested with this method: (1) absorption against a concentration gradient, and (2) inhibition of transport when energy-yield-