Diffusion equilibria for the isolated frog's kidney

Abstract

The concn. of urea from an external urea-Locke soln. was fully demonstrated for the active isolated frog kidney, the formation of a glomerular filtrate being impossible during the concentrating process. The proof of this latter consists in washing pairs of fresh kidneys in Locke soln. for 20 min., retaining one member of each pair for a grouped analysis, the companion tissues being immersed for 45 min. in urea-Locke, containing 40 mgm. urea per 100 ml. and subsequently analyzed. After the initial washing the mean urea concn. was 34 mgm. per 100 ml.; after reimmersion in urea-Locke it rose to 51 mgm. urea per 100 ml. When the reimmersion was made in urea-cyanide-Locke[long dash]containing also 40 mgm. urea per 100 ml.[long dash]the concn. found was 35.6 mgm. urea per 100 ml, which is very close to what may be expected for a passive equilibration. Many similar expts. were also carried out in which the external urea concs. were varied. The results in all cases supported the foregoing findings. When the reimmersions after the initial washing were made for 45 min. in Locke or cyanide-Locke containing no urea, the mean difference of urea content between the active and inactive tissues did not exceed 2 mgm. urea per 100 ml. Xanthydrol determinations of the urea in the frog''s kidney gave identical results with the urease method used. This latter was subjected to a detailed examination in so far as it could have any bearing on the results obtained.