KINETICS OF THE EXCRETION AND UTILIZATION OF XYLOSE

Abstract

The time change of the plasma concentration of xylose after a single rapid intraven. injection can be represented by the equation, [xi]= ae-at + be-[beta]t, if the disturbances in the first few minutes are neglected. The theory assumes that the rate of diffusion from the plasma into the tissues is proportional to the concn. difference between the 2 volumes. 8 exps. in 4 mongrel bitches, varying in weight from 16.4 to 20.7 kgm., showed that the constants [alpha] and [beta], the ratio b/a, the excretion constant (rate of excretion per unit plasma concn.), the utilization constant (rate of utilization per unit plasma or tissue concn.), and the proportion of xylose excreted by the kidney, were independent of the quantity injected. The latter was varied from 1 to 4 g. per kilo of body weight. The mean excretion constant was 0.363 and the mean utilization constant 0.175 mg. per minute. The mean proportion of xylose excreted was 63.45% of the quantity injected, with a standard error of 2.85. The equivalent plasma volume represents 23% of the body weight. The volume of distribution of xylose is 26 or 30% of the body weight, according as the rate of utilization is assumed proportional to the plasma concn. or proportional to the tissue concn.