Urea Excretion in White Rats and Kangaroo Rats as Influenced by Excitement and by Diet

Abstract

Renal excretion of urea was studied in kangaroo rats and in white rats. In inulin infusion experiments with kangaroo rats the urea clearance decreased relative to the glomerular filtration rate in the course of an experiment, blood sampling accelerated this decrease. To investigate if excitement could be the cause of the depression, the urea excretion was studied in undisturbed and in excited kangaroo rats, using the true endogenous creatinine clearance as a measure for the filtration rate. Results showed: (a) that in the completely undisturbed kangaroo rat the amount of urea excreted in the urine is as high and sometimes exceeds the amount filtered, even when the tubular reabsorption of water is high so that a considerable back diffusion of urea could be expected. (b) If the kangaroo rat is disturbed the urea clearance decreases relative to the filtration rate. In experiments with white rats the effects of excitement and of diet were studied. The urea/creatinine clearance of ratio decreased to about half the pre-excitement level when the rats became excited. Rats on a high protein diet (40% protein) showed a urea/creatinine clearance ratio twice as high as that of rats on a low protein diet (10% protein). Results reported do not conform with the filtration-rediffusion theory for urea excretion.