Some Nutritional and Physiological Factors Affecting the Urinary Excretion of Acid Soluble Peptides in Rats and Women

Urinary excretion of acid soluble peptide (ASP)-form amino acids was lower in rats deprived of protein than in rats fed on a 20% casein or 20% gluten diet. However, the amino acid pattern of urinary ASP was similar among each of the three dietary groups, suggesting that urinary ASP is mainly endogenous origin under these nutritional conditions.

College women who were given a meat-free protein diet for 3 days after 10 days’ protein deprivation excreted 1.4 times the amount of ASP-form amino acids during protein deprivation.

The rate of urinary excretion of ASP-form amino acids in the state of protein deprivation was proportional to the metabolic body size of organisms as far as rats and women were concerned.

Streptozotocin-induced diabetic rats excreted two times the amount of ASP-form amino acids compared with normal rats. This suggests that endogenous protein catabolism doubled in diabetic rats.

When labelled urinary ASP was injected into rats, approximately 40% of the label was recovered as urinary ASP within 24 hr. This excretion rate was far higher than that after the injection of free leucine.

The rate of urinary excretion of ASP-form amino acids correlated with that of N^τ-methylhistidine in rats.

These results favor the hypothesis that urinary ASP reflects the catabolism of body proteins.     

Effect of dietary protein, alfalfa, and zeolite on excretory patterns of 5',5',7',7'-[3H]zearalenone in rats

A series of experiments was conducted to determine how dietary protein, alfalfa, or zeolite influence the excretory patterns of zearalenone (Z), a uterotropic mycotoxin synthesized by Fusarium fungi. Rats were fed diets containing 16.3% casein, 40% casein, 11.2% casein + 25% alfalfa, or 25% casein + 25% alfalfa. Also fed were diets containing 0, 1, 2, or 5% anion exchange zeolite. Tracer doses of [3H]Z were administered either as a constituent of the diet or as a topical application on the skin at the base of the skull. When Z was administered orally, no differences were seen in the fraction of the dose excreted in urine or feces as a result of varying dietary levels of alfalfa and protein. Topical doses resulted in rats fed 25% casein + 25% alfalfa or 40% casein excreting more Z in urine than those fed 25% alfalfa or 16.3% casein. Fecal excretion of Z was greatest for rats fed 25% casein + 25% alfalfa whereas rats fed 40% casein excreted more fecal Z than those fed 16.3% casein. Feeding Z to rats receiving dietary zeolite resulted in a positive correlation between dietary zeolite and fecal excretion of Z but a negative correlation with urinary excretion of Z. Topical administration of Z produced a positive correlation between dietary zeolite and fecal Z excretion but no effect on urinary excretion. It may be concluded that protein and alfalfa treatments alleviate Z toxicosis through increased metabolism whereas zeolite binds Z in the digestive tract to prevent absorption.     

The influence of dietary protein on ascorbic acid metabolism in rats

1. d-Glucuronolactone reductase, l-gulonolactone oxidase, uronolactonase, dehydroascorbatase, l-gulonate dehydrogenase and l-gulonate decarboxylase have been measured in the tissues of rats fed on diets containing variable amounts of protein. Rats fed on a protein-free or a 2% casein diet for 15 days showed a marked decline in the activities of d-glucuronolactone reductase, l-gulonolactone oxidase, uronolactonase and dehydroascorbatase in the liver, and no change in l-gulonate dehydrogenase and l-gulonate decarboxylase activities in the kidney when compared with rats fed on diets containing 9%, 18% or 25% casein. Giving diets containing 60% or 88% casein to rats did not appreciably alter the activities of uronolactonase, dehydroascorbatase, l-gulonate dehydrogenase and l-gulonate decarboxylase, but inhibited considerably the activities of d-glucuronolactone reductase and l-gulonolactone oxidase in the liver, resulting in decreased synthesis of ascorbic acid. 2. Rats fed on a 25% casein diet showed maximal weight gain, higher tissue reserve of ascorbic acid and higher urinary excretion of both ascorbic acid and glucuronic acid when compared with rats fed on diets containing lower or higher amounts of protein.     

Control of urea synthesis and ammonia utilization in protein deprivation and refeeding.

Rats were fed a standard diet (20% protein) or a protein-free diet for up to 65 days. After 20 days on the protein-free diet some rats were refed the standard diet. By the 20th day the rats fed the protein-free diet showed a blood ammonia level approximately 70% higher than controls and urea excretion decreased approximately 20-fold. At this time the liver acetylglutamate decreased to approximately one-fifth of the initial and control levels, returning to normal after 3 days of refeeding the standard diet, with a concomitant increase in urea excretion. The protein-deficient diet resulted in decreased activities of liver enzymes related to ammonia metabolism. All enzyme activities assayed returned to normal values rapidly upon refeeding the standard diet, except hepatic carbamylphosphate synthetase, glutamine synthetase, and glutaminase, which took approximately 1 month to return to control values. The findings presented here are consistent with the view that urea production is controlled, at least under certain conditions, by acetylglutamate, the physiological activator of carbamylphosphate synthetase.     

Effects of dietary linoleic acid on blood pressure and renal function in subtotally nephrectomized rats

The effect of a high linoleic acid diet on blood pressure, renal function, and urinary prostaglandin excretion was studied in rats with decreased renal mass. Subtotally nephrectomized (5/6 nephrectomy) male rats received either a 15% linoleic acid (high linoleic acid, HLA) diet containing 20% safflower oil or a 0.28% linoleic acid (low linoleic acid, LLA) diet containing 20% coconut oil. Sham-operated rats were also placed on either HLA or LLA diet. The subtotal nephrectomized rats developed similar degrees of hypertension during the first 3 weeks after subtotal nephrectomy. However, 4 weeks after subtotal nephrectomy, the rats on HLA diet had significantly lower blood pressure than the rats on LLA diet [HLA 152 +/- 3 (mean +/- SE) mm Hg versus LLA 171 +/- 3 mm Hg]. This difference persisted until termination of the experiment at 7 weeks after subtotal nephrectomy (HLA 159 +/- 7 mm Hg versus LLA 192 +/- 6 mm Hg). The GFR measured 7 weeks after subtotal nephrectomy was significantly lower in both of the subtotally nephrectomized groups. However, the HLA subtotal nephrectomized rats had significantly higher GFR than the LLA-treated rats (HLA 0.23 +/- 0.05 ml/min 100 g versus LLA 0.12 +/- 0.02 ml/min/100 g, P less than 0.05). There was no difference in the GFR or blood pressure in the sham-operated rats treated with HLA or LLA diet. PGE2 excretion was lower in the two groups of subnephrectomized rats, but there was no difference between the HLA and LLA treated rats. Urinary 6-ketoPGF1 alpha was not decreased by subtotal nephrectomy and there was no difference between the dietary groups. However, TXB2 excretion was higher in the groups with subtotal nephrectomy, but there was no difference between the two dietary groups. In conclusion, the HLA diet attenuates the rise in blood pressure after subtotal nephrectomy in the rat and preserves renal function. There was no difference in urinary excretion of PGE2, 6-keto-PFG1 alpha, or thromboxane B2 between the two dietary groups.     

Renal reabsorptive capacity for alpha 2u-globulin in the adult male rat.

Adult male rats were maintained on 0, 5, 10, 15, and 20% casein diets to produce a series of animals having serum alpha 2u-globulin levels varying linearly from a normal of 31 micrograms/ml to a minimum of 13 micrograms/ml. In this way, it was possible to titrate endogenously the renal reabsorption and urinary excretion of this low molecular weight protein. The average maximal reabsorption rate (Tm) was established to be 9.7 micrograms/min and was reached at a renal filtered load (F alpha 2u) of 13.6 micrograms/min. These data were expressed in terms of a Tm:F alpha 2u ratio of 0.71. Below this value, the reabsorption declined from 70% to 50% of the F alpha 2u. Above 0.71, where F alpha 2u is less than the Tm, the reabsorption increased to 80-90%. It was observed that the fractional renal uptake of the alpha 2u-globulin varied linearly with the filtered load.     

Quantitative aspect of the myofibrillar protein turnover in transient state on dietary protein depletion and repletion revealed by urinary excretion of Nτ-Methylhistidine

The fractional rates of synthesis and breakdown of myosin and actin in skeletal muscle of younn adult male rats were measured during 2 weeks of ad libitum feeding of a protein-free diet, and 8 days of refeeding with an adequate protein diet. Daily urinary excretion of N^τ-Methylhistidine (3-methylhistidine) by the N^τ-methylhistidine pool of the body gave the fractional breakdown rate of the myosin-actin pool. The fractional synthesis rate of the myosin-actin pool was calculated from the fractional breakdown rate and the size of N^τ-methylhistidine pool in the body. The feeding of the protein-free diet resulted in a decreased in body weight and a decrease in daily urinary excretion of N^τ-methylhistidine. Refeeding caused an increase in body weight and a progressive increase in daily urinary excretion of N^τ-methylhistidine. At the start of the experiment, the fractional breakdown rate of the myosin-actin pool was 4% per day and with prolonged protein depletion, the rate decreased to 1.25% per day. The fractional synthesis rate also decreased more rapidly than the breakdown rate. On refeeding for one day with an adequate protein diet, the fractional synthesis rate increased from 0.75 to 5.75% per day. Accumulation of skeletal muscle protein by refeeding was accompanied by a difference between the faster rate of synthesis and slower rate of breakdown even though the fractional breakdown rate increased during the rehabilitation period.     

Long-term ingestion of ammonium increases acetylglutamate and urea levels without affecting the amount of carbamoyl-phosphate synthase

Rats were fed the following diets: standard (20% protein), high-protein (80%), protein-free, standard plus ammonium and protein-free plus ammonium for six weeks. The standard plus ammonium diet was prepared to contain ammonia equivalent to that supplied by the high-protein diet. Addition of ammonium acetate (20% by mass) to the 20% protein or protein-free diets results in 2.3- and 10-fold increases of urea excretion respectively, without increase of carbamoyl-phosphate synthase. Supplementation of the standard diet with ammonium increases the mitochondrial content of acetylglutamate from 830 to 1590 pmol/mg protein, and of the protein-free diet from 130 to 1040 pmol/mg. However, ingestion of ammonium did not increase the activity of acetylglutamate synthase. Therefore the efflux of acetylglutamate from mitochondria was determined. After 30 min at 37 degrees C liver mitochondria from rats on standard diet released 61% of the initial acetylglutamate while mitochondria from animals on standard plus ammonium diet released only 20%. These results indicate that ingestion of ammonium increases the content of acetylglutamate in rat liver by decreasing its efflux from mitochondria. This effect is similar to that produced in mice by a high protein diet [Morita et al. (1982) J. Biochem. (Tokyo) 91, 563-569]. However, while the high-protein diet increases carbamoylphosphate synthase content, the ammonium diet does not.     

Enhanced phosphorylation of a nucleolar 110-kDa protein in rat liver by dietary manipulation

RNA polymerase 1 activity and nucleolar volume have been reported to increase in hepatocytes from rats fed a protein-free diet. Phosphorylation in vitro of a 110-kDa protein was enhanced in nuclei and nucleoli from livers of rats fed a protein-free diet. In nuclear extracts the 110-kDa protein in heat-treated nuclei was much more phosphorylated than from control liver. In contrast, casein kinase activity in the nuclear extract from control liver was comparable to that from livers of rats fed a protein-free diet. Nuclear extracts from control rat liver and livers of rats fed a protein-free diet were fractionated by DEAE-cellulose column chromatography. Casein kinase II (NII) eluted at around 0.17 M NaCl scarcely phosphorylates the 110-kDa protein. Chromatography of the nuclear extract from livers of rats fed a protein-free diet, but not from control liver, yielded fractions which eluted at 0.21-0.25 M NaCl and predominantly phosphorylated the 110-kDa protein. The phosphorylation of 110-kDa protein was not appreciably affected by a heparin concentration of 5 micrograms/ml, which completely inhibited casein kinase II. In addition, phosphorylation of the 110-kDa protein in liver nucleoli from rats fed a protein-free diet showed a lower sensitivity to heparin than that in control rat liver nucleoli. These results suggest that enhanced phosphorylation of the nuclear 110-kDa protein in livers from rats fed a protein-free diet is due to the induction of a 110-kDa protein kinase distinct from casein kinase II.     

Effect of feeding protein deficient diet on phospholipid turnover and protein kinase C mediated protein phosphorylation in rat brain

Feeding of protein deficient diet is known to alter the transmembrane signalling in brain of rat by reducing total protein kinase C (PKC) activity. Phospholipid metabolism regulates the activation of PKC through generation of second messengers and the extent of PKC activation accordingly influences the magnitude of phosphorylation of its endogenous substrate proteins. Thus it was speculated that ingestion of protein deficient diet may modify the turnover rate of membrane phospholipids and magnitude of phosphorylation of endogenous substrate proteins of PKC. The experiments were conducted on rats fed on three different types of laboratory prepared diets viz. casein (20% casein), deficient (4% protein, rice flour as source of protein) and supplemented (deficient diet supplemented with L-lysine and DL-threonine) for 28 days. The metabolism of phosphoinositides (PIs) and phosphatidyl choline (PC) was studied by equilibrium labeling with [3H] myo inositol and [14C methyl] choline chloride respectively. The phosphorylation of endogenous substrate proteins of PKC was studied by using 32P-gamma-ATP followed by SDS-PAGE and autoradiography. The results suggest that in deficient group, there is an increased incorporation of [3H] myo inositol in PIs and inositol phosphate pool in comparison to the casein group. The phosphatidyl inositol (PI) turnover reduced, although there was a marginal increase in the phosphatidyl inositol monophosphate (PIP) and phosphatidyl inositol bis phosphate (PIP2). Supplementation of diet showed a reversal of the pattern towards control to a considerable extent. In the deficient group, PC metabolism showed an increased incorporation of [14C methyl] choline in choline phospholipids but decreased incorporation in phosphoryl choline in comparison with the casein group. The increase in total PC contents was significant but marginal in residue contents. The turnover rate of PC increased only marginally and that of residue declined. Supplementation of diet reduced the total contents of PC and residue, but the turnover rate of PC and residue remained still higher. Phosphorylation of endogenous proteins showed four different proteins of 78, 46, 33 and 16 kDa to be the substrates of PKC in casein group. In deficient group, phosphorylation of these proteins increased markedly while supplementation of diet had a reversing effect rendering the values to be intermediate between casein and the supplemented group. The changes in phospholipid metabolism and in phosphorylation of endogenous substrate proteins of PKC suggest that dietary protein deficiency causes alterations in transmembrane signalling mechanism in rat brain. These effects are partially reversed by improving the quality of proteins in the diet.     

Stimulative effect of dietary protein on the phosphorylation of p70 S6 kinase in the skeletal muscle and liver of food-deprived rats

The effect of dietary protein on p70S6k phosphorylation was examined in rats starved for 18 h and then fed either a 20% casein diet (20C) or a protein-free diet (0C). Refeeding the 20C diet, but not the 0C diet, increased p70S6k phosphorylation in both the skeletal muscle and liver. The plasma insulin concentrations were the same after refeeding the 20C or 0C diet, suggesting that a combination of dietary protein and insulin may be required to stimulate p70S6k phosphorylation.     

Influence of a high protein diet on the urinary and fecal excretion of calcium in albino rats

Albino rats (Sprague-Dawley) of mean weight 100 g were divided into four groups and given for 7 days a balanced diet. They were then placed in metabolic cages for fifteen days and fed diets containing different quantities of casein: 18% (D18), 36% (D36), 50% (D50) and 72% (D72). The levels of total calcium, inorganic phosphorus, alkaline phosphatase activity, total proteins and urea were determined. The urinary and fecal excretion of calcium were determined on specimens of urine and stool collected every two days. The metabolic balance of nitrogen was also estimated. The results show there is not a linear relationship between a high protein diet and plasma protein levels, but a progressive body calcium loss was observed with the increase of casein in the diet, which confirms what other workers have already suggested.     

Changes in Creatine and Urea Formation in Rats Fasted and Fed Low Protein Diets

Changes in the time course of the urinary excretion of creatinine, creatine and urea, and the activities of kidney transamidinase and liver urea-cycle enzymes were investigated in rats fasted and fed on a 10% casein diet and 10% casein diets supplemented with 10% glycine and/or 1.4% arginine.

The urinary total-creatinine of the fasted rats increased extremely during fasting for 7 days, while that of the animals given the 10% casein diet supplemented with glycine and arginine rose exceedingly on the 3rd day and thereafter no significant change was observed. Most of the increase of total-creatinine could be accounted for by the increase of creatine. The activity of kidney transamidinase in the fasted rats decreased in the 3rd day and thereafter kept nearly constant. The transamidinase activity of rats fed on the 10% casein diet after giving a protein-free diet for 5 days increased in the 3rd day. An inverse relation was observed between the urinary creatine and the transamidinase activity. The urinary urea increased in the rats fasted or fed on the 10% casein diets with the supplement of glycine and/or arginine. In fasting, the activities of liver urea-cycle enzymes, except arginase, had a tendency of increasing with the lapse of time. The arginase activity remained more or less constant. The reason of the extreme increase of urinary creatine during starvation was discussed.     

Rapid dephosphorylation of eIF4E by dietary protein in the skeletal muscle and liver of food-deprived rats

The effect of dietary protein on eIF4E phosphorylation was examined in rats starved for 18 h and then fed on either a 20% casein diet (20C) or a protein-free diet (0C). Refeeding with the 20C diet, but not the 0C diet, resulted in partial dephosphorylation of eIF4E in both the skeletal muscle and liver. The results suggest that the dephosphorylation of eIF4E in response to food intake was regulated by the increase in plasma amino acid concentration that occurred after feeding with the 20C diet.     

Effect of a protein-free diet on muscle protein turnover and nitrogen conservation in euthyroid and hyperthyroid rats.

Although protein turnover in skeletal muscle is increased in hyperthyroidism and decreased in hypothyroidism, a deficient protein intake tends to increase serum T3 (tri-iodothyronine) while decreasing muscle protein turnover. To determine whether this diet-induced decrease in protein turnover can occur independent of thyroid status, we have examined muscle protein turnover and nitrogen conservation in hyperthyroid rats fed on a protein-free diet. After inducing hyperthyroidism by giving 20 micrograms of T3/100g body wt. daily for 7 days, groups of euthyroid and hyperthyroid animals were divided into subgroups fed on basal and protein-free diets. Muscle protein turnover was measured by N tau-methylhistidine excretion and [14C]tyrosine infusion. Urinary nitrogen output of euthyroid and hyperthyroid animals fed on the protein-free diet was also measured. Although hyperthyroidism increased the baseline rates of muscle protein synthesis and degradation, it did not prevent a decrease in these values in response to protein depletion. Furthermore, hyperthyroid rats showed greatly decreased nitrogen excretion in response to the protein-free diet, although not to values for euthyroid rats. These findings suggest that protein depletion made the experimental animals less responsive to the protein-catabolic effects of T3.     

Protein intake conditions the diuresis seen after relief of bilateral ureteral obstruction in the rat

Natriuresis and diuresis occur in experimental animals after release of bilateral ureteral obstruction. Accumulation of urea and/or other natriuretic factors during the interval of complete obstruction may play a role in the ensuing postobstructive diuresis. The present experiments examine the potential role of dietary protein intake in conditioning the magnitude of the postobstructive diuresis after unilateral release of bilateral ureteral obstruction of 24-hr duration in the rat. Rats were fed isocaloric diets containing high (40% casein) or low (6% casein) protein for 4 weeks prior to obstruction. Rats fed a high protein diet had greater urine flows and fractional excretion of sodium and potassium after relief of obstruction than rats fed a low protein diet. Increased excretion of urea accounted for only part of the greater diuresis seen in rats fed a high protein diet. Hence, greater accumulation of other natriuretic factors during the period of obstruction in rats fed a high protein diet must play a role in the increased diuresis seen in this group of animals after release of obstruction.     

Lunatoic Acid A,a Morphogenic Substance Inducing Chlamydospore-like Cells in Some Fungi

The effect of the addition of 0.26 % free tryptophan (Trp) to a 20 % casein diet containing 6 mg of nicotinic acid per 100 g of diet on the ratio of N¹-methyl-2-pyridone-5-carboxamide (2-py) plus N¹-methyl-4-pyridone-3-carboxamide (4-py) to -methylnicotinamide (MNA) excretion was investigated in rats. The urinary excretion of MNA, 2-py and 4-py, respectively, increased statistically significantly with the feeding of a 0.26% Trp (the same as the content of the 20% casein diet) supplemented 20% casein diet, although it did not increase with the feeding of a 40% casein diet, compared with in the case of the 20 % casein diet [Agric. Biol. Chem., 52, 1765 (1988)]. So, the total urinary excretion of Nam and its metabolites was 1.8 times higher in the group fed the Trp supplemented diet than in the group fed the 20 % casein diet. However, the ratio of 2-py plus 4-py to MNA excretion was much lower in the group fed the Trp supplemented diet than in the group fed the 20 % casein diet (13.16 ± 3.75→5.49 ± 2.25). This decreased ratio was considered to be partially due to a decrease in the 4-py forming MNA oxidase, which decreased significantly with the feeding of the Trp supplemented diet. Furthermore, the metabolic fate of Trp was greatly affected by the form of Trp, free or bound.     

Phospholipid metabolism and protein kinase C mediated protein phosphorylation in dietary protein deficiency in rat lung

Nutritional deprivation of proteins decreases the protein kinase C (PKC) activity in rat lung. The activity of (PKC) is influenced by lipid metabolism. Changes in PKC activity may influence phosphorylation of its substrate proteins in the tissues. Therefore, alterations in phospholipid metabolism and PKC mediated protein phosphorylation in dietary protein deficiency in rat lung were envisaged. The study was conducted on rats fed on three different types of diet viz., casein (20% protein), deficient (4% protein, rice flour as source of protein) and supplemented (deficient diet supplemented with L-lysine and DL-threoning). Feeding of protein deficient diet caused reduction in incorporation of [3H] myo-inositol in the total phosphoinositides in lungs and an increase in total inositol phosphate pool. There was a significant reduction in the contents and turnover rate of phosphatidyl inositol and phosphatidyl inositol monophosphate. Supplementation of diet with L-lysine and DL-threonine had a reversing effect on total pool of phosphoinositides and, the metabolism of phosphatidyl inositol bisphosphate and phosphatidyl inositol. In phosphatidyl choline metabolism, the dietary protein deficiency led to a decrease in incorporation of [14C-methyl] choline-chloride in total phospholipids. In contrast, its incorporation increased in phosphatidyl choline pool. The contents of phosphatidyl choline and residue, incorporation of [14C-methyl] choline-chloride in them and their turnover rate also increased. Supplementation of diet had a reversal effect on most of these parameters. Phosphorylation of proteins of 84, 47, 35 and 16 kDa was identified to be mediated by PKC. In dietary protein deficiency, phosphorylation of all these proteins, except that of 47 kDa, increased. Supplementation of diet reversed the pattern except that of 84 kDa. The findings suggest that changes in phospholipid metabolism in dietary protein deficiency may effect the activity of PKC thereby influencing the phosphorylation of its substrate proteins and hence associated functions that may lead to pathophysiology of lung.     

Soy protein,casein, and zein regulate histidase gene expression by modulating serum glucagon

Glucagon has been postulated as an important physiological regulator of histidase (Hal) gene expression; however, it has not been demonstrated whether serum glucagon concentration is associated with the type and amount of protein ingested. The purpose of the present work was to study the association between hepatic Hal activity and mRNA concentration in rats fed 18 or 50% casein, isolated soy protein, or zein diets in a restricted schedule of 6 h for 10 days, and plasma glucagon and insulin concentrations. On day 10, five rats of each group were killed at 0900 (fasting), and then five rats were killed after being given the experimental diet for 1 h (1000). Rats fed 50% casein or soy diets showed higher Hal activity than the other groups studied. Rats fed 50% zein diets had higher Hal activity than rats fed 18% casein, soy, or zein diets, but lower activity than rats fed 50% casein or soy diets. Hal mRNA concentration followed a similar pattern. Hal activity showed a significant association with serum concentrations of glucagon. Serum glucagon concentration was significantly correlated with protein intake. Thus the type and amount of protein consumed affect Hal activity and expression through changes in serum glucagon concentrations.     

Renal reabsorption of low molecular weight proteins in adult male rats: alpha 2u-globulin

Urinary proteins are reabsorbed by the renal tubule cells by two processes, the first for high molecular weight (HMW) and the second for low molecular weight proteins (LMW). The purpose of this report is to establish that alpha 2u-globulin, the sex-dependent, major urinary protein of the adult male rat, is reabsorbed in the kidneys by the general mechanism for LMW proteins. Parameters such as clearance rates were determined to show that alpha 2u is reabsorbed by a process comparable to that for lysozyme. The aminoglycoside, gentamicin, was observed to inhibit the reabsorption of alpha 2u in a dose-dependent fashion. It increased the alpha 2u excretion rate from 4.2 to 13.5 micrograms/min; the clearance was increased from a normal of 0.33 to 0.91 ml/min. The excretion rate for alpha 2u was also increased by the injection of lysozyme from a normal of 7.4 to 18.1 micrograms/min. The effect of lysozyme was dose-dependent and reversible. Although gentamicin and lysozyme each increased the excretion of alpha 2u, they had no effect on albumin. Both were equally effective as inhibitors of alpha 2u reabsorption and were 80% as effective as sodium maleate. It is suggested that alpha 2u is reabsorbed by a mechanism which is shared with other LMW proteins. Furthermore, this process is independent of the one which serves to translocate HMW proteins such as albumin.