Urine Urea Concentration Research Articles

Kidney composition and renal concentration ability in young rabbits.

1. The water, sodium, urea, potassium and ammonia concentrations of the kidney cortex and inner medulla of adult rabbits, and of rabbits 1, 4, 14 and 21 days old, were measured after mild dehydration. The urine osmolarity and serum and urine urea concentrations were also measured.2. Potassium and ammonia showed no consistent variation in the different parts of the kidney or at the different ages. Sodium concentrations expressed as m-equiv/100 g fresh weight were about twice as high in the medulla as in the cortex at all ages.3. The medulla/cortex ratio of urea concentration increased markedly between the fourteenth and twenty-first day after birth. So also did the urine osmolarity of the mildly dehydrated animals.4. The rise in the medulla/cortex urea ratio between birth and 21 days, and the even higher ratio found in adult animals, was due to a decrease in the concentration of urea in the cortex rather than to an increase in its concentration in the medulla.

Function of a renal autograft after extirpation of the other kidney

A study was made on eight dogs of autografted preserved kidneys after extirpation of the other which was left undisturbed for some time. We found that during the first days after the removal of the undisturbed kidney, there was an increase of diuresis and of the urinary concentrations of urea and creatinine secreted by the transplanted preserved kidney. Filtration per minute increased 5–10 times, and approached the initial combined filtration of the original and transplanted kidneys, and at times even exceeded it. Tubular reabsorption approached the value of that of the undisturbed kidney. At various times after extirpation of one kidney, polyuria of various durations was observed.

Effect of diet on distribution of urea and electrolytes in kidneys of sheep.

In sheep and other mammals on normal protein intake, the kidney urea concentration showed an increase from cortex to papilla, and the urine urea concentration was usually higher than in the tissue. In sheep on low-protein diet, the highest urea concentration was found in the inner stripe of the outer zone of the medulla, where it was 5–15 times the urine urea concentration. At the tip of the papilla, it was only slightly higher than in the urine. The electrolyte distribution in kidneys of sheep on normal and low protein diet differed in one important respect. In normal protein sheep, the electrolyte concentration in the papilla was usually higher than in the urine. In contrast, in low protein sheep, it was lower in all zones of the kidney than in the urine. However, because of the accumulated urea in the outer zone of the medulla, the osmotic concentration in this zone equaled the osmotic concentration of the urine.

Urea excretion in the camel.

The nitrogen excretion was studied in the one-humped camel, Camelus dromedarius. When a growing camel was maintained on a low N intake (dates and hay) the amount of N excreted in the form of urea, NH3 and creatinine decreased to 2–3 gm/day. This decrease was caused by a drop in urea excretion from 13 gm to 0.2–0.5 gm/day. Urea given intravenously during low N intake was not excreted but was retained. (The camel like other ruminants can utilize urea for microbial synthesis of protein.) The renal mechanism for urea excretion was investigated by measuring urea clearance and glomerular filtration rate during a period of 7 months. During normal N intake about 40% of the urea filtered in the glomeruli were excreted in the urine while during low N intake only 1–2% were excreted. The variations in urea clearance were independent of the plasma urea concentration and of glomerular filtration rate, but were related to N intake and rate of growth. No evidence of active tubular reabsorption of urea was found since the urine urea concentration at all times remained higher than the simultaneous plasma urea concentration. The findings are not in agreement with the current concept for the mechanism of urea excretion in mammals. It is concluded that the renal tubules must either vary their permeability to urea in a highly selective manner or secrete urea actively.

A Simplified Method for Measurement of Creatinine Clearance

The multitude of substances whose “clearances”, or rate of excretion in relation to blood concentration, have been proposed as tests of kidney function indicates that a satisfactory clinical procedure is yet to be devised. The use of urea, as proposed by Moller, McIntosh and Van Slyke, is in our experience the simplest of the more sensitive tests, since it involves only one blood sample and does not require the ingestion of the test substance. But since the rate of urea excretion is less with low urine volume than with high, function tests can be compared only as a percentage of an average empirical normal for urine volumes above or below 2 cc. per minute. There are, therefore, certain advantages in using a test substance whose excretion is independent of urine volume. Creatinine, the use of which was proposed by Rehberg, is such a substance. This method as described has the disadvantage of requiring ingestion of creatinine, and analysis of urine and 2 samples of blood plasma. The development by Van Slyke and Cope of a clinical method for the determination of urea clearances suggested that a similar procedure might be devised for the creatinine clearance which, if practical, would considerably simplify the test. In the method of Van Slyke and Cope, the ratio between urine and blood urea concentrations is determined by a direct comparison, without determining the actual concentration in either. In the method here described, the same principle is applied except that creatinine is used. In order to increase the concentration of creatinine in the blood and urine, creatinine is administered to the subject by mouth, and water given at hourly intervals during the test if there is any question of the subject's ability to urinate.

UREA CLEARANCE TEST AS AN INDEX OF RENAL FUNCTION

The urea clearance studies in twenty-one cases of Bright's disease, which formed the nucleus of the preceding paper in this series,1 will be correlated in the following pages with various other tests and measures of renal function. Van Slyke, McIntosh, Moller, Hannon and Johnston2 and Johnston3 have compared the urea clearance with the concentrations of urea, uric acid, creatinine and hemoglobin in the blood, the excretion rate of phenolsulphonphthalein and the urea concentration ratio in nephritic subjects. Our work permits us to compare our findings concerning the blood urea clearance in subjects with Bright's disease with the concentrations of urea, uric acid and creatinine in the blood, the blood count (hemoglobin and red blood cell count), the two hour test for renal function and the urea concentration ratio urine urea concentration blood urea concentration METHODS Urea in blood and urine was determined by the gasometric urease method of Van Slyke,4