N-acetyl-β-glucosaminidase Research Articles

Verapamil limits shockwave-induced renal tubular damage in vivo.

Previous investigations on Madin Darby Canine Kidney (MDCK) cells demonstrated the protective effect of verapamil against shockwave-induced tubular dysfunction. In the present study, we investigated whether verapamil is also protective against shockwave-induced damage in vivo. Male rates were randomly assigned to three groups: verapamil (N = 18) (Group I), control (N = 18) (Group II), or sham treatment (N = 4) (Group III). Groups I and II were treated with 500 shockwaves to each kidney with the Dornier MFL 5000 at 18 kV. Animals assigned to Group III received only anesthesics. Verapamil was given to the animals in Group I for 5 days starting 1 day before shockwave exposure. Urine was collected for 8 hours the day before and immediately, 1.7, and 28 days after shockwave exposure (SWE) for measurement of volume, osmolality, hemoglobin, protein, N-acetyl-beta-glucosaminidase (NAG), beta 2-microglobulin (beta 2M), sodium, and creatinine. Kidneys were perfused and removed for histologic study 1, 7, and 28 days after SWE in six animals of Groups I and II. Blood was taken in these rats (Day 1 after SWE) for the determination of creatinine and sodium and the calculation of the creatinine clearance (CCr) and the fractional excretion of sodium (FENa). After SWE, there was strong diuresis and significantly increased excretion of NAG and beta 2M in the controls, while urine osmolality decreased. These changes were significantly less pronounced in the verapamil-treated rats. The CCr was higher and FENa lower than in the latter group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of potassium deficiency and gossypol on urinary N-acetyl-β-glucosaminidase excretion in the rat

Some men receiving gossypol in China developed elevated urinary N-acetyl-β-glucosaminidase (NAG) levels and hypokalemia. Since idiopathic hypokalemia occurs in China, hypokalemic nephropathy may have caused the elevated NAG levels. To learn if gossypol is directly nephrotoxic, we treated rats with a normal or low potassium diet with or without gossypol. The low potassium diet produced high NAG levels rather than the gossypol. This indicates the importance of differentiating hypokalemic nephropathy from drug nephrotoxicity in regions where idiopathic hypokalemia occurs.

Alteration of in vitro bone metabolism and tooth formation by zinc

1. The effects of zinc on bone metabolism and tooth formation was examined in organ cultures of calvaria and tooth germ, and in cell cultures of osteoblast-like cells, MC3T3-E1. 2. Treatment of calvaria with zinc (10, 100 μM) for 4 days both increased alkaline phosphatase (ALP) activity in bone and reduced the secretion of N-acetyl β-glucosaminidase from bone, without affecting bone mineral or collagen content. The increase in ALP activity produced by zinc (10 μM) was inhibited neither by actinomycin D (5 μg/ml) nor by cycloheximide (0.5 μg/ml). 3. Treatment of MC3T3-E1 cells with zinc (50, 100 μM) for 25 days also increased ALP activity, but reduced calcium content in cells and in the matrix layer. 4. These results indicate that zinc increases ALP activity in osteoblasts without affecting de novo enzyme synthesis, and that it inhibits bone mineralization, in accordance with the inhibition of osteoclastic activity. 5. Treatment of tooth germ with zinc (100 μM) for 7 days also produced an increase in ALP activity and inhibition of mineralization. These results indicate that the increased ALP activity produced by zinc is a common phenomenon in hard tissues, and, further, that zinc inhibits mineralization during tissue formation.

An association between the lysosomal enzyme NAG and urinary free cortisol and platelet imipramine binding

Urinary levels of the lysosomal enzyme N-acetyl-β-glucosaminidase (NAG) were significantly correlated to levels of 24-hour urinary free cortisol in a group of panic disordered patients. In a separate study of healthy controls NAG levels showed a trend toward association with platelet imipramine binding density. A hypothesis is proposed that NAG levels may be proportional to the density of postsynaptic serotonin receptors.

Does the Administration of Systemic Radiographic Contrast Media Influence the Acute Changes in Renal Physiology Following Exposure to Extracorporeal Shock Waves in Dogs?

Five anesthetized dogs were studied for 4 to 5hours after administration of extracorporeal shock waves to one kidney, the contralateral organ serving as control. Repetitive major doses of the nonionic monomeric radiographic contrast medium (CM) iohexol were injected intravascularly before and after application of the extracorporeal shock waves for further provocation of kidney function. Urinary excretion of electrolytes, N-acetyl-β-glucosaminidase (NAG) and kallikrein, clearances of creatinine, inulin and para-amino-hippuric acid (PAH), serum aldosterone level and plasma renin activity (PRA) were determined.On the exposed side there was a significant fall in urinary osmolality. Effective renal plasma flow (ERPF) was reduced and glomerular filtration rate (GFR) was unchanged; thus filtration fraction (FF) was increased. Extraction of PAH was reduced, and true renal plasma flow was unchanged.Urinary osmolality on the control side was unchanged. There was a fall in ERPF and increased GFR; therefore, FF increased.The mean rise of PRA in the exposed kidney was significant after shock waves. Urine volume and urinary excretion of electrolytes and kallikrein were stable bilaterally.Relating the results to those obtained in identical canine experiments without CM, simultaneous administration of CM does not seem to significantly influence the changes in kidney function parameters caused by extracorporeal shock waves in the dog.

Association of levels of N-acetyl-beta-glucosaminidase with specific psychiatric symptoms in bipolar patients

The levels of N-acetyl-β-glucosaminidase (NAG) in urine from 35 patients with bipolar affective disorder were compared with scores for the 90 items (symptoms) of the Symptom Checklist (SCL-90). There were significant negative correlations between NAG levels and 23 of the SCL-90 variables (symptoms). These symptoms could be grouped into the following categories: anxiety, unusual or psychotic thinking, suicidal thinking, dysphoria, irritability, nausea, headaches, memory problems, and loss of interest. Serotonin abnormalities may play a role in the production of many of these symptoms. The hypothesis that NAG could be a marker for a serotonin activity is discussed.

Urinary excretion of N-acetyl-β-glucosaminidase and β-galactosidase by patients with epilepsy

In an effort to detect active renal tubular dysfunction in 74 epileptic patients being treated with antiepileptic drugs (AEDs), we measured the urinary activity of two lysosomal enzymes, N-acetyl-β-glucosaminidase (NAG) and β-galactosidase (β-gal). The heterogeneity of the types of seizures and therapeutic regimens permitted us to examine the potential differences in AED effects. We also examined the chronological changes in the urinary excretion rates of NAG and β-gal in 132 healthy controls, aged 3 months to 37 years. Increased NAG excretion rates (defined as ≥ 2 S.D. compared with age-matched controls) were found in 36.5% of the patients. Valproic acid was highly associated with this increase, and in combination with potassium bromide caused the highest levels of NAG excretion. Among the patients taking carbamazepine, only 11.1% exhibited high levels of NAG in urine. Children under 1 year of age showed higher levels of NAG excretion than older patients. In spite of the abnormally high urinary excretion of NAG, we could not detect any signs of renal dysfunction by urinalysis and measurement of blood urea nitrogen and serum electrolytes. We cannot exclude the possibility that the increased levels of urinary NAG in epileptic patients might be due to renal tubular enzyme induction by AEDs.

Changes in Renal Function after Extracorporeal Shock Wave Lithotripsy in Patients with Solitary Functioning Kidneys: Long-Term Follow-Up

Nine of twelve consecutive patients with a solitary functioning kidney treated for renal stone by extracorporeal shock wave lithotripsy (SWL) with the modified Dornier HM3 lithotripter were evaluated before and 20 months (range 12-24 months) after treatment by detailed renal cortical and tubular function tests. Urinary excretion of the renal tubular enzymes N-acetyl-β-glucosaminidase (NAG), alkaline phosphatase (ALP), and kallikrein and of albumin and β2-microglobulin was unchanged. Clearances of creatinine (CCr), inulin (CIN) and para-aminohippuric acid (CPAH) and filtration fraction (FF) were constant, as were serum levels of creatinine, urea, and β2-microglobulin. In seven of the nine patients, however, CIN was decreased at follow-up by a mean of 15% (range 5% to 54%), and CPAH was decreased by a mean of 30% (range 3% to 58%) in six of the nine patients. Plasma renin activity (PRA) and serum aldosterone were stable, and no patient developed new-onset hypertension.

Effect of l-penicillamine hydantoin, an analogue of glutathione, on rat liver glutathione peroxidase, reductase and transferase reactions

In soluble fractions prepared from rat liver homogenates, l-penicillamine hydantoin appeared to be, on the basis of SH consumption measurements, a substrate for glutathione peroxidase but not transferase reactions. When glutathione is incubated with rat liver soluble proteins in the presence of penicillamine hydantoin, formation of oxidized glutathione is inhibited. Calculations from Lineweaver Burk plots point out that inhibition by l-penicillamine hydantoin of the peroxide-dependent oxidations of glutathione is mixed, since both apparent K m and V max values are modified. Preincubation of rat liver soluble proteins with l-penicillamine hydantoin led to a progressive inactivation of glutathione peroxidase. The kinetics of this inactivation process with respect to time and inactivator concentration were studied. Inclusion in the preincubation mixture of SH-containing molecules such as dithiothreitol, l-cysteine or glutathione protected the enzyme against inactivation. However, none of these molecules and neither hydantoin, Triton X-100, phenol, nor dialysis could reverse the enzyme from inactivated to activated form. Mitochondrial glutathione peroxidase was inhibited and inactivated by l-penicillamine hydantoin to the same extent as its cytosolic counterpart. Modifications by penicillamine hydantoin of various subcellular markers enzymes (lactate dehydrogenase, N-acetyl β-glucosaminidase, arylsulfatase C, butyryl-CoA dehydrogenase, lauryl-CoA and glycolate oxidases) were of weak amplitude consisting of either inhibition, inactivation or stimulation,

Interdependence of polymorphonuclear neutrophils and macrophages stained for N-acetyl- β-glucos-aminidase in lavage effluents from toluene diisocyanate-exposed rat lungs

Male Sprague-Dawley rats were exposed to toluene diisocyanate (TDI) concentrations between 0.082 and 1.087 ppm for 4 h, and pulmonary lavage was carried out 24 h after initiation of the exposure. Cells recovered from the lavage effluents of TDI-exposed rat lungs were identified and counted, then pulmonary macrophages (PMs) resulting from cytocentrifuged preparations were examined for N-acetyl- β-glucosa-minidase (NAG) cytochemical staining. Exposure to TDI led to a parallel and concentration-dependent increase in the number of polymorphonuclear neutrophils (PMNs) and the proportion of PMs stained for NAG, suggesting that the same primary event initiates the two cell responses.

Comparative acute nephrotoxicity of salicylic acid, 2,3-dihydroxybenzoic acid, and 2,5-dihydroxybenzoic acid in young and middle aged Fischer 344 rats

Experimental evidence suggests that the oxidative metabolites 2,3- and 2,5-dihydroxybenzoic acid (DIOH) may be responsible for the nephrotoxicity of salicylic acid (SAL). In the present study, enzymuria in conjunction with glucose (GLU) and protein (PRO) excretion were used as endpoints to compare the relative nephrotoxicity of SAL with 2,3- and 2,5-DIOH. In addition, the effect of age on enzymuria and GLU and PRO excretion following treatment with SAL or 2,3- and 2,5-DIOH was investigated because the elderly are at greater risk for SAL-induced nephrotoxicity. Three and 12-month male Fischer 344 rats were administered either no treatment, vehicle, SAL, 2,3-DIOH, or 2,5-DIOH at 500 mg/kg p.o. in 5 ml/kg corn oil/DMSO (5:1). Effects of these treatments on functional integrity of renal tissue was assessed from 0–72 h after dosing by measurement of urinary creatinine, GLU, and PRO, as well as excretion of proximal and distal tubular renal enzymes. Enzymes measured as indicators of proximal tubular damage were N-acetyl- β-glucosaminidase (NAG), gamma glutamyltransferase (GGT), alanine aminotransferase (ALT). and alkaline phosphatase (AP), while urinary lactate dehydrogenase (LD) and aspartate aminotransferase (AST) were measured as indicators of distal tubular damage. In comparison to 3-month vehicle-treated rats, 2,3- and 2,5-DIOH caused a significant increase between 0–8 h in excretion of urinary GLU and activities of AST, NAG, and LD, with peak effects occurring between 4–8 h. Toxic effects of either metabolite were not evident beyond 24 h, and toxicity of 2,5-DIOH was significantly greater in comparison to 2,3-DIOH. SAL treatment resulted in similar effects on enzymuria as well as GLU and PRO excretion, but peak effects did not occur until 16–24 h, and often persisted until 72 h after dosing. Maximal enzymuria in response to SAL treatment was significantly greater in 12- vs. 3-month rats for AST, NAG, and LD. In response to 2,3-DIOH treatment, the maximal response was significantly greater in 12- vs. 3-month rats for LD and AST, and for NAG in response to 2,5-DIOH treatment. The results of this study suggest that both 2,3- and 2,5-DIOH are nephrotoxic metabolites of SAL, but implicate 2,5-DIOH as the more potent

Changes in urinary proximal tubule parameters in neonatal rats exposed to cadmium chloride during pregnancy

Pregnant Sprague-Dawley rats were injected intraperitoneally with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.0 or 2.5 mg kg-1 on days 8, 10, 12 and 14 of gestation. On postnatal day (PND) 3, 12 or 49, the offspring were examined for 8- or 24-h urinary excretion of beta 2-microglobulin (beta 2-m), metallothionein (MT) and urinary activity of three proximal tubular enzymes: gammaglutamyl transferase (GGT), alkaline phosphatase (ALP) and N-acetyl-beta-glucosaminidase (NAG). Treatment with CdCl2 did not affect growth or survival of offspring. Significant decreases in the urinary excretion of GGT, ALP and NAG were observed on PND 3, at both doses. Exposure to 4 x 2.5 mg kg-1 resulted in functional deficit of the proximal tubule on PND 3, as evidenced by the significant increase in beta 2-m. Except for a slight but significant increase of beta 2-m in 49-day-old males, all the other urinary parameters returned to control values on PND 12. There was no effect on MT. Results from this study show that prenatal exposure to CdCl2 can induce significant changes in the kidney biochemistry of rats in the early postnatal period.

Urinary N-Acetyl-β-glucosaminidase and the Selection of Children for Radiologic Evaluation After Urinary Tract Infection

Urinary levels of N-acetyl-β-glucosaminidase (NAG) were measured in 147 consecutively enrolled children younger than 13 years of age with urinary tract infection to determine whether elevated levels were a predictor of urologic abnormalities. The children were classified as having cystitis if results of 0 or 1 of the following tests were positive and as having pyelonephritis if results of ≥2 tests were positive: (1) temperature >38°C, (2) serum C-reactive protein >1 mg/dL, (3) erythrocyte sedimentation rate >25 mm/h, and (4) 1-deamino-8-D-arginine vasopressin-renal concentrating protein <810 mOsm/kg. Urinary NAG to creatinine ratios did not distinguish cases of cystitis from those of pyelonephritis. Urinary NAG was useful in identifying children with cystitis who had vesicoureteral reflux of grades II through V. Of 6 children with cystitis and vesicoureteral reflux, 5 had levels of NAG more than 1 SD above the mean, whereas of 75 children without vesicoureteral reflux, only 15 had such an elevation (P = .003). Of those children with a normal NAG level, 60 (98.4%) had normal radiologic evaluation results, and only 1 child (1.6%) had vesicoureteral reflux. Levels of NAG did not identify children with pyelonephritis who had vesicoureteral reflux. It is concluded that (1) urinary NAG is of no value in localizing the site of urinary tract infection, and (2) an NAG level within 1 SD of the mean in a child with cystitis indicates a low risk of urologic abnormalities, and radiologic evaluation may be omitted unless infection recurs.

Acute Physiological Changes in Canine Kidneys Following Exposure to Extracorporeal Shock Waves

Nine anesthetized dogs were studied for four to five hours after administration of extracorporeal shock waves to one kidney, the contralateral organ serving as control. Urinary excretion of electrolytes, N-acetyl-β-glucosaminidase (NAG) and kallikrein, clearances of creatinine, inulin and para-amino-hippuric acid (PAH), serum aldosterone level and plasma renin activity (PRA) were determined.On the exposed side there was a significant increase in urinary flow and urinary NAG excretion, and a significant fall in urinary osmolality. Effective renal plasma flow (ERPF) was reduced and glomerular filtration rate (GFR) unchanged, thus filtration fraction (FF) was increased. Extraction of PAH was significantly reduced compared with the control kidney.On the control side there was a significant increase in urinary flow and excretion of electrolytes, and a significant fall in urinary osmolality. GFR was increased and ERPF unchanged. FF therefore increased also on this side. The mean rise of PRA in the exposed kidney was higher than in the control kidney, the difference being not significant (p = 0.09).Our results may indicate a triggering of the renin-angiotensin system, and an effect on proximal tubular function following exposure of extracorporeal shock waves. (J. Urol, 143:1280-1283, 1990)

Effects of prenatal methylmercury exposure on urinary proximal tubular enzyme excretion in neonatal rats

The basal developmental pattern of excretion of 3 proximal tubular enzymes was determined in 8-h urinary specimens from neonatal rats. Gammaglutamyltransferase (GGT), alkaline phosphatase (ALP), and N-acetyl-β-glucosaminidase (NAG) activities were measured at 3, 6, 9 and 12 days after birth. Subsequently, methylmercury chloride (CH 3HgCl), known to induce foetotoxic changes in the proximal tubule was administered on 8 days, 10 and 12 of gestation at 3 or 6 mg/kg and its effects on the enzyme activities were examined. Dose-related increases in the 3 enzyme activities occured at dose levels that produced no maternal or postnatal toxicity, nor overt morphological malformation of the kidney. The peak of enzyme activities averaged about 200% and 130% of the control values for GGT, ALP, and NAG respectively, and occured on days 3 and 6 in the treated groups. Urinary enzyme activities returned to the control levels from days 6 to 12. Our data point to the possibility of detecting CH 3HgCl-induced prenatal effect on the kidney by measuring the 8-h urinary excretion of enzymes by rats in the early postnatal period.

Effects of Cycloheximide and Actinomycin D on Glycosidase Activities in the Cotyledons of Legume Seeds Following Imbibition

Summary The activities of α-galactosidase (EC 3.2.1.22), β-galactosidase (EC 3.2.1.23), α-mannosidase (EC 3.2.1.24) and N-acetyl β-glucosaminidase (EC 3.2.1.30) were assayed in extracts from the cotyledons of pea ( Pisum sativum L.), cowpea ( Vigna unguiculata [L.] Walp.) and mung bean ( Vigna radiata [L.] Wilcz.) following imbibition of seeds for periods up to 3 days at 24 °C. Cycloheximide or actinomycin D provided over the first 24 h did not inhibit the development of any of these enzyme activities, except for α-galactosidase from pea (cv. Telephone). Cycloheximide inhibited the incorporation of label from 14 C-labelled amino acids into protein by 93.4 % (pea) up to 98.0 % (cowpea). We conclude that acid glycosidase activities in imbibing cotyledons of these species generally result entirely from rehydration of enzyme molecules formed during seed development.

The distribution of N-acetyl-β-glucosaminidase, β-glucuronidase, acid α-naphthyl acetate esterase and α-naphthyl acetate esterase in subpopulations of thymocytes, bone marrow cells and other lymphoid organs in mice

1. 1. Thymocytes, bone marrow lymphocytes, as well as lymphocytes from spleen, lymphoid nodes and peripheral blood were obtained from BALB/c mice. Subpopulations of BALB/c bone marrow T-lymphocyte precursors and immature (small) and mature (large) thymocytes, as established by the percentage of terminal deoxynucleotidyl transferase (TdT) and peanut agglutinin (PNA) positive cells, were obtained by centrifugation on discontinuous density gradients. 2. 2. The activities of N-acetyl-β-glucosaminidase (NAG), β-glucuronidase (BG), acid α-naphthyl acetate esterase (ANAE) and α-naphthyl acetate esterase (NAE) were determined by enzymatic assays of cell extracts of the diverse T-lymphocyte subpopulations, in order to follow their evolution with the maturation of the T-lymphocytes in the thymus. 3. 3. These activities were compared with that determined in lymphocytes from spleen, lymphoid nodes and peripheral blood. 4. 4. The glucidases BG and NAG and the esterases ANAE and NAE present a high decrease in their activities from bone marrow T-lymphocyte progenitors to immature thymocytes. 5. 5. BG, NAG and ANAE activities undergo an about 3-fold increase with the evolution of the thymocytes from small to large cells. Whereas the level of the NAE activity decreases (2-fold) with that evolution of the thymocytes. 6. 6. Lymphocytes from spleen and lymphoid nodes exhibit activities of the glucidases and, specially, the esterases marked by higher than those of thymocyte populations. 7. 7. Peripheral blood lymphocytes also present NAG, ANAE and NAE activities higher than in thymocytes, but their BG activity is lower.

Aortic enzymes and lactate in high altitude-raised and cholesterol-fed rabbits

1. (1) Fourteen male rabbits born at elevation 4000 ft (first experimental series) were transferred at age of 2 months to elevation 12470 ft and raised there for 18 weeks. Half of the animals remained on a commercial rabbit chow (group H) while the other half was on the same diet supplemented with cholesterol (group C). Eight male rabbits raised at sea level served as controls (group S). Intima-media homogenates from the thoracic aortas were assayed for lactate dehydrogenase (LDH), malate dehydrogenase (MDH), lipoamide dehydrogenase, pyruvate kinase (PK), phosphofructokinase (PFK) and the lysosomal hydrolases β-glucuronidase and N-acetyl-β-glucosaminidase (NAGA). Aortic lactate and glucose were also measured. 2. (2) Thirty-two male rabbits (second experimental series) were subdivided into 4 groups. Rabbits were fed a cholesterol-supplemented diet not only at high altitude (8 rabbits matching group C) but also 8 animals raised at sea level. The degree of atherosclerosis in the aortas of these 4 groups was assessed by measuring the aortic cholesterol contents. Plasma cholesterol was also determined. 3. (3) In the aortas of the rabbits of group H the activity of PK was significantly elevated, and the activity of the lysosomal hydrolases significantly decreased compared with aortas of group S rabbits. There was no difference in the other enzyme activities or in the aortic glucose and lactate content of these groups. 4. (4) Cholesterol feeding of the animals of group C resulted in a significantly increased activity of the lysosomal hydrolases as well as of LDH and PK. The lipid analyses (second experimental series) revealed a trend to a lower concentration of aortic cholesterol in the high altitude than in the sea level animals, both fed a cholesterol diet, in spite of the higher plasma cholesterol concentrations in the high altitude animals. 5. (5) The low aortic lysosomal hydrolase activities in the high altitutde rabbits are in accord with their comparatively lower susceptibility to experimental atherosclerosis. This metabolic feature may be due to a lower degree of exposure of these aortas to injurious factors, such as infections or lower blood pressure. The elevated activity of PK without increased lactate content in group H animals seems to parallel the well-known general adaptation of the organism to high altitude hypoxia, and does not indicate a metabolic switch toward anaerobic glycolysis.

Aminoglycoside-related nephrotoxicity in the premature newborn

The nephrotoxicity of gentamicin and amikacin was compared during presumed sepsis in 107 premature neonates. To examine the possibility that nephrotoxicity was directly associated with the clinical conditions of "sepsis," a control group of 26 chloramphenicol-treated newborns was also studied. Two markers of proximal renal tubular injury, N-acetyl-beta-glucosaminidase (NAG) and beta 2-microglobulin, were measured in 6-hr aliquots of urine. Because urine creatinine excretion increased with postconception age, markers were expressed in terms of excretion rate rather than per milligram of creatinine. The NAG excretion rate was significantly higher in gentamicin-treated patients (138 +/- 10 U/min, mean +/- SE) than in amikacin-treated patients (85 +/- 7 U/min) but did not differ between patients treated with amikacin and those treated with chloramphenicol (81 +/- 11 U/min). Excretion of beta 2-microglobulin did not differ among the three patient groups. We conclude that amikacin may be less nephrotoxic than gentamicin in the premature newborn.

Further studies of the response of kidney Lysosomes to aminoglycosides and other cations

Rat renal cortical lysosomes were isolated in 0.3 M sucrose containing 1 mM EDTA by differential centrifugation. Lysosomes were incubated in isotonic sucrose or isotonic glycine with various concentrations of endogenous and exogenous compounds at 37° for 1 hr. Lysosomes were resedimented, and the N-acetyl- β-glucosaminidase (NAG) activity was measured in the supernatant fraction and the disrupted pellet and the percentage of total NAG released was calculated. Gentamicin and its C 1 and C 2 components had similar potencies for inhibiting NAG release from lysosomes at low concentrations. The release of alpha-galactosidase and beta-galactosidase from lysosomes was also inhibited by streptomycin and gentamicin. Mepacrine at low concentrations stabilized lysosomes and at high concentrations disrupted lysosomes. This drug also enhanced the effect of low concentrations of gentamicin on lysosomes. Inositol hexaphosphoric acid was a potent antagonist of the effect of low concentrations of gentamicin and mepacrine on lysosomes. Rats were treated with gentamicin at doses of 40, 80 and 160 mg/kg for 1 and 3 days. NAG excretion in gentamicin-treated groups as compared to saline controls was unchanged at day 1. Only the 160 mg/kg treatment group showed a tendency toward elevated renal cortical NAG at day 1 (P < 0.06). All treatment groups had elevated renal cortical NAG at day 3, while the 160 mg/kg group also had elevated NAG excretion. Lysine, arginine, l-canavanine and polymyxin B all affected NAG release from lysosomes in vitro. Lysine enhanced the disruptive effect of high gentamicin concentrations on lysosomes. Ferric and ferrous ions, tested over widely varied concentrations, inhibited NAG release at low concentrations while enhancing NAG release at high concentrations. We therefore conclude that the nephrotoxicity of aminoglycoside and other endogenous and exogenous renally excreted cationic compounds may be produced by their effects on lysosomes in the proximal renal tubule.