The rate of absorption of hexoses and pentoses

Abstract

With the method described in the preceding abstract, the rate of absorption of the sugars referred to in Table I has been investigated. Over 100 rats have been used for obtaining the data recorded in this table. The absorption coefficients represent an average of 1, 2 and 3 hour periods in the case of galactose and glucose, and of 1, 2, 3, 4 and 5 hour periods in the case of the other sugars. It will be noted that a relatively slight change in the sugar molecule affects the rate of absorption very markedly. The ketosugar fructose is absorbed at a rate of less than one half of that of glucose. The isomeric change from glucose to mannose reduces the rate of absorption to one-fifth. Pentoses are absorbed at still slower rates. All this indicates that the intestinal membrane is possessed of a high degree of selective permeability for sugars.

When the amount of sugar that is absorbed is plotted against time, a straight line is obtained, as is illustrated in Figure 1. The maximum deviation from the mean was ±10 per cent, which is as close an agreement as can be expected from a biological method such as the one used for this work. The straight lines in Figure 1 extend to a point where arbout SO to 70 per cent of the sugar originally introduced has been absorbed. From this it follows that the rate of absorption remains constant in spite of the diminution of the amount and also the concentration of sugar present in the intestine; or that the rate of absorption is independent of both factors.