THE RELATIVE RETENTION OF INFUSED CHLORIDE, UREA AND WATER

Abstract

A technique for studying the relative retentions of constantly infused solutes and water is described, and theoretical aspects of the isorrheic state (constant urine flow or solute excretion with constant infusion rate) are developed. The velocity constants of excretion (rate of excretion per unit load) of chloride, water, and urea have been ascertained in the dog. They may be used to characterize those critical concs. of infusion fluid and urine at which neither solute nor water is retained from an infusion, relative to one another. For chloride, expressed as NaCl, these concs. are approx. 6 and 17 mg./cc. For urea the only such cone. is approx. 35 mg./cc. (when the simultaneously infused chloride is less than 17 mg./cc.) under the conditions of these expts. The law of exponential decay is regarded as the underlying pattern followed by the excretion of threshold as well as no-threshold substances, and factors which relate to the modification of this pattern are examined. Excretion rate of chloride can be expressed not only as a function of load but also as a function of the distortion, or departure from normal, of the ratio of chloride to non-chloride space, induced by this load. The excretion of urea is uncomplicated by a distortion factor. Rehberg''s concept of threshold conc. for ions like chloride is extended and a simple technique for determining and expressing such threshold concs. is suggested.