The Rate of Excretion of Galactose.

Abstract

It has been shown in a previous paper 1 that the percentage of absorbed galactose that is excreted in the urine of the rat increases with increasing length of absorption, in spite of the fact that the rate of absorption remains constant from hour to hour. Thus in 1 hour 27.4% appeared in the urine, in 2 hours 41%, in 3 hours 51%, and in 4 hours 60.5%. The present report is an attempt to elucidate the basis of this phenomenon.

Experimental. In figure 1 of the preceding paper the amounts of galactose excreted in the urine have been plotted against the amounts absorbed. The amounts excreted, as shown in this figure, can be plotted against time with the aid of the values recorded in Table I of the preceding paper, using 182 mg. per hour for the average rate of absorption of galactose alone, 74 mg. per hour for galactose from the galactose-glucose mixture, and 27 mg. per hour for galactose from lactose. This has been done in Fig. 1 of the present report. From Fig. 1 the values for excretion in Table I have been read off. It should be emphasized that these values are for an ideal excretion, since they have been obtained under experimental conditions which exclude a lag in sugar excretion. The values in parentheses, which are taken from a previous paper, 1 indicate how much galactose can actually be excreted during each hour. It will be noted that the percentage of absorbed galactose that is excreted in the urine increases from hour to hour. This makes it appear as if there were an hourly increment in the rate of excretion, and conversely an hourly decrement in the rate of utilization, but the phenomenon is actually due to a lower rate of excretion in the first hour, represented by a break in the straight line in Fig. 1. If one calculates the values from 0 to 1 hour, from 1 to 2 hours, and so on, one finds that after the first hour 52 mg. are utilized, and 130 mg. (or 71.4%) are excreted per hour for each consecutive hour.