The distribution and excretion of insulin in man

Abstract

A technique has been devised for performing inulin clearances in man, which is a great simplification on the method used by earlier workers.The simplification is threefold.A single injection is used in lieu of a large priming injection followed by a sustained infusion to maintain the blood inulin concentration. As a result of this the blood concentration is constantly falling throughout the experiment, so that some difficulty may be experienced in getting the exact mean blood concentration for each observation.Urine specimens were voided in the natural way, and catherisation of the bladder followed by washing out with saline was not practised. It was felt that such a drastic procedure was not warranted by a clinical experiment.This is an obvious source of error on account of large differences between blood and urine concentration, but if the urine flow is kept at a high level by giving the subject large quantities of water to drink this can be minimised.A marked improvement in the manner of estimating blood inulin has been introduced. This method is both simpler and of greater accuracy than the original ones used in the estimation of inulin. It is on account of the greater accuracy that a relatively small single injection can be used.This method is much simpler than a similar one which has been introduced by Alving, Rubin and Miller in America and which Is fairly generally used in that country now. It is possible, however,that their method may be of slightly greater accuracy. I am sceptical of the use of this method without removing the blood glucose. The authors state that it is applicable at blood concentrations of over 30 mg. /100 c.c.The colour due to fructose in Herbert's method is 88% developed after 15 minutes, and this follows a rectilinear relationship. At this time the colour due to glucose is negligible. By the other method, however, the specimens are incubated for 1 hour, and though the proportions of the reagents are different, one feels that there must be a considerable colour development due to glucose.The results obtained in a series of subjects by this method are analysed and discussed, and certain of the observations are compared with synchronous urea clearances.In the course of these investigations the distribution of inulin in the human body is also studied, and the fact that inulin is excreted by a simple physical process of filtration is demonstrated by observations showing that the rate of excretion increases proportionally to the blood inulin concentration. As further proof of filtration, it has also been shown that when the fall of blood concentration is plotted logarithmically against time, a rectilinear relationship results.