Inulin Volume of Distribution as a Measure of Extracellular Fluid in Dog and Man

Abstract

Inulin space was detd. by establishing a uniform distr. of this substance throughout all the extracellular compartment in active interchange with the plasma water, by means of a priming dose and a constant intraven. infusion for a sufficient period of time (1-2 hrs. in dogs, about 6 hrs. in man). Then, simultaneously, a blood sample was taken, the bladder emptied by catheter and rinsed, and the infusion abruptly discontinued. Subsequently, the urine was collected for a period of time sufficient to insure the excretion of at least 98% of the inulin in the body (4-6 hrs. in dogs, 10-18 hrs. in man). The quantity of inulin (in mg.), divided by the plasma concn. (in mg./ml.), equals the vol. of distr. in ml. This vol. ranges from 20.9-23.2% of body wt. (avg. 21.6) in dogs and 15-16% in man, as compared with larger spaces obtained simultaneously with SCN-, Na24, Na22 and Br.