The Effect of Feeding Protein and Urea on the Renal Concentrating Process 1

Abstract

The role of dietary protein in the treatment of renal disease remains a controversial one, in part because the influence of diets high or low in protein upon normal renal function is not completely understood. In the rat much evidence has accumulated that high-protein intakes lead to renal hypertrophy (1-3) and that low-protein diets may be associated with impairment of some renal functions (4). Pullman, Alving, Dern, and Landowne (5) (6), creatinine (7), urea (8), sodium and potassium (9) were also determined. The "t" test of "Student" was used in analyzing the data. Each subject was studied after three days on a LowProtein diet, containing approximately 20 grams of protein per day, and a High-Protein diet, containing 150 to 200 grams of protein per day. The latter was achieved by the use of 100 to 200 grams per day of a high-protein, low-sodium supplement.5 Both diets were approximately isocaloric; in some subjects the low-protein diet consisted chiefly of carbohydrate, in others fat predominated. Two subjects were studied on a Regular diet, containing about 90 gramns of protein per day. Other variations in dietary regimen will be described under Results.RESULTS (Table I) Effect of low-vs. high-protein diets on renal concentrating ability, inulin clearance and urea clearance (Figure 1) Maximum urinary solute concentration and maximum osmolal U/P ratio were invariably higher after three days of a high-protein intake than after a diet low or normal with respect to protein. The increases in maximum urinary osmolality with ingestion of large amounts of protein varied from 87 to 332 mOsm. per K. This occurred in association with an increased basal urinary flow containing from 1.2 to 5 times the quantity of solutes excreted on a low-protein diet. The maximum capacity of the kidneys to reabsorb water free of solute (TmOH2O) was likewise increased by 15 to 50 per cent in five subjects by feeding protein.Inulin clearance was slightly higher in each of five subjects on a high-protein regimen than on a diet low in protein. At the high urine flows obtained during mannitol diuresis, the clearance of 5 Melactin, supplied by E. R. Squibb and Co.635

Renal Concentrating Mechanisms in Newborn Infants. Effect of Dietary Protein and Water Content, Role of Urea, and Responsiveness to Anti-Diuretic Hormone *

“…These findings in infants are in agreement with those reported in adults by Epstein and co-workers (20). In Group 2, values for Posm were consistently greater following high protein intake, suggesting that the higher values for urinary osmolality observed may have resulted in part from a greater degree of dehydration or ADH release.…”

“…Epstein and co-workers (20) found in adults that acute urea loading had no effect on maximal urine osmolality or Tmce2O and concluded that the effect of chronic administration of protein or urea was achieved by promoting an adaptive response by the renal tubules. In the present study similar results were obtained in infants given low or intermediate urea loads.…”

“…Protein or urea added to the diet of adults has been shown by Epstein, Kleeman, Pursel and Hendrikx (20) to produce a significant increase in maximal urine osmolality at low rates of urine flow during hydropenia and in the maximal rate of reabsorption of free water (TmCH11O) during mannitol diuresis.…”

24-h hydration status: parameters, epidemiology and recommendations

“…Infants fed protein-rich cow's milk or cow's milk formulas showed higher maximum Uosm values ( Figure 2). In adults, mean maximum Uosm with a high protein intake was 300 mosm/kg higher than with a low protein intake (Epstein et al, 1957b;Levinsky et al, 1959;Macaron et al, 1975;Koppeschaar et al, 1985). The difference in mean maximum Uosm between a sodium intake of 20 and 150 mmol/24-h was 74 or 94 mosm/kg (Koppeschaar et al, 1985).…”

Studies on the Renal Concentrating Mechanism. Ii. Effect of Small Acute Changes in Solute Excretion*

“…Small urea loads did not alter urine osmolality in the subjects of Epstein, Kleeman, Pursel and Hendrikx (19) who were on a low protein diet. It is possible that the decrease in U/P ratio which accompanies an increase in solute excretion was obscured by an effect of urea itself in subjects on a restricted protein intake.…”