Evidence in Support of the Filtration-Reabsorption Theory of Urine Formation in the Dog.

Abstract

In these experiments the amount of urea and glucose excreted in the urine under varying conditions is compared with the amount of similar substance calculated to have been filtered through the glomeruli on the basis of the Filtration-Reabsorption Theory. The amount of urea or glucose filtered is calculated from the following formulae which are adaptations of those proposed by Rehberg 1 :

Creatinine is assumed to have no threshold value. To make the blood creatinine determinations more reliable creatinine is given by stomach tube 3 hours before samples are collected. All blood concentration figures are averages for the period of observation.

Fifteen experiments have been performed to date.

The amount of urea present in the urine has never exceeded the amount estimated to have been filtered. When urea is injected intravenously an increase in the output of urea is obtained which is approximately proportional to the rise in blood urea concentration except when a spontaneous decrease in the amount of filtrate occurs. Such a decrease counteracts to a large extent the rise in blood urea concentration. Euphyllin administered intravenously increases the amount of urea excreted in the urine and this increase is roughly proportional to increases in the calculated amount of filtrate formed and in the estimated amount of urea filtered.

The amount of glucose appearing in the urine after the administration of large doses of phlorhizin is, within the limits of error of the methods employed, equivalent to the amount estimated to have filtered through the glomeruli.