Low nitrogen diets preserve nutritional status but not residual renal function in rats with severe renal failure

The effects of low nitrogen diets (oral and parenteral) on nutritional status and residual renal function were evaluated in rats with experimentally induced severe renal failure (partial nephrectomy) and compared with the effects of a normal protein diet. Non-uremic rats were used as controls. Muscle protein synthesis was significantly lower in uremic rats fed a normal protein diet than in those fed low protein diets. Values for serum insulin-like growth factor 1 (IGF-1) were significantly lower than for controls in all uremic groups as were the wet and dry weights of skeletal muscle. The glomerular filtration rate was studied after 3 wk of nutritional intervention. Serum creatinine concentration was lower and creatinine clearance greater in uremic rats given the low nitrogen dietary treatments (both oral and parenteral) compared with those fed the normal protein diet. However, the glomerular filtration rate determined with 51Cr-EDTA clearance did not differ between uremic rats with normal and low protein intake. Thus, a low nitrogen diet had positive effects on uremic toxicity and did not compromise nutritional status. The results do not, however, establish a favorable influence on residual renal function and emphasize the need for reliable methods for studying dietary effects on renal function in uremia.     

Salt induces myocardial and renal fibrosis in normotensive and hypertensive rats

BACKGROUND: The detrimental effects of high dietary salt intake may not only involve effects on blood pressure and organ hypertrophy but also lead to tissue fibrosis independently of these factors. METHODS AND RESULTS: The effect of a normal (1%) or high (8%) sodium chloride diet on myocardial and renal fibrosis was assessed by quantitative histomorphometry in spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto rats (WKYs). The effect of salt on transforming growth factor-beta1 (TGF-beta1) gene expression was assessed by Northern blot hybridization. A high-salt diet from 8 to 16 weeks of age resulted in increased blood pressure and left ventricular and renal hypertrophy in both WKYs and SHRs. Marked interstitial fibrosis was demonstrated in the left ventricle (LV), glomeruli, and renal tubules and in intramyocardial arteries and arterioles but not in the right ventricle. The collagen volume fraction increased significantly after high-salt diet in the LV, intramyocardial arteries and arterioles, glomeruli, and peritubular areas in both WKYs and SHRs. In the kidneys, glomerular and peritubular type IV collagen was also increased. There was overexpression of TGF-beta1 mRNA in the LV and kidneys in both rat strains after a high-salt diet (all P<0.001). CONCLUSIONS: High dietary salt led to widespread fibrosis and increased TGF-beta1 in the heart and kidney in normotensive and hypertensive rats. These results suggest a specific effect of dietary salt on fibrosis, possibly via TGF-beta1-dependent pathways, and further suggest that excessive salt intake may be an important direct pathogenic factor for cardiovascular disease.     

Selective dietary restriction of protein and calorie intakes prevents spontaneous proteinuria in male MWF rats

BACKGROUND/AIMS: Previous observations indicate that protein and calorie restrictions can affect the course of renal disease progression. We compared the effects of selective protein and calorie restriction on glomerular hemodynamics and proteinuria in a model of spontaneous glomerular injury in the rat. METHODS: Three groups of male MWF rats were assigned to three different diets: standard diet (ST, 19% protein, 3.4 kcal/g), low protein (LP) and low calorie (LC). Proteinuria and systolic blood pressure were periodically measured. Glomerular hemodynamics and tuft volume were determined after 2 months of dietary treatment. RESULTS: The effective mean protein intake was 3.4 +/- 0.4, 1.6 +/- 0.2, and 3.2 +/- 0.2 g/day/rat, respectively, for the ST, LP, and LC diets, while caloric intake averaged 60 +/- 7, 59 +/- 9, and 30 +/- 2 kcal/day/rat. Both LP and LC diets significantly prevented proteinuria (104 +/- 32, 36 +/- 9, and 18 +/- 8 mg/day, respectively, in the three groups). The systolic blood pressure was unaffected by the diets. The LC diet induced lower body and kidney weights than the ST diet. The glomerular filtration rate was slightly but significantly increased by the LP diet, but not by the LC diet (0.64 +/- 0.14, 0.81 +/- 0.08, and 0.67 +/- 0.12 ml/min, respectively, for ST, LP and LC diets). The glomerular hydraulic pressures were not affected by the diets. No differences were also observed in glomerular volume. The incidences of glomerulosclerosis and tubulointerstitial changes were comparable in ST and LP diets and completely absent in the LC diet group. CONCLUSION: These results indicate that restriction of both protein and calorie intakes prevents spontaneous proteinuria in male MWF rats by preventing deterioration of glomerular perm-selective functions.     

The vestibular system modulates masseter muscle activity

The effects of feeding a 1% corn oil-9% menhaden oil or beef tallow diet on the early phase of diabetic nephropathy in BHE/cdb rats was studied. The diet groups were subdivided into rats with or without impaired glucose tolerance. Those fed menhaden oil had renal hypertrophy, mild albuminuria, decreased creatinine clearance, increased urea clearance, and more severe lesion scores than rats fed beef tallow. No differences in glomerular filtration rate, Na+, K+-ATPase activity, sorbitol dehydrogenase, or inositol 1, 4, 5-phosphate were observed. Beef tallow-fed rats had higher serum triglyceride levels and renal cholesterol levels. Renal and hepatic fatty acid profiles reflected the fatty acid profile of the dietary fat. These results suggest that beef tallow conferred a protective effect on the renal tissues of these diabetes-prone rats.     

Hepatocyte growth factor in human breast milk

BACKGROUND: Glomerular accumulation of macrophages/monocytes (M/M) is a typical early feature in the course of anti-thymocyte serum (ATS)-induced nephritis. We have previously shown that glomerular synthesis and expression of monocyte-chemoattractant protein-1 (MCP-1) occurs before influx of M/M and a neutralizing anti-MCP-1 antibody reduced this cell infiltrate by one third. The present study was undertaken to test the effect of two angiotensin II type 1 (AT1) receptor antagonists, losartan and irbesartan, on ATS-stimulated MCP-1 expression as well as glomerular influx of M/M. METHODS: Treatment of rats with either losartan or irbesartan was started 24 h before administration of ATS. After 24 h, MCP-1 mRNA expression was evaluated by RT-PCR and Northern blots. MCP-1 protein was determined by Western blots and chemotactic factors released from isolated glomeruli were measured by chemotactic assay. Kidney sections were stained for rabbit IgG, complement C3, and M/M (ED1 antigen). RESULTS: Both AT1-receptor antagonists caused a significant, but not total reduction in MCP-1 mRNA and protein expression 24 h after injection of ATS. Treatment with losartan or irbesartan also reduced the chemotactic activity of isolated glomeruli from nephritic animals. Quantification of ED1-positive cells revealed that losartan as well as irbesartan reduced glomerular M/M invagination in nephritic rats by approximately 30-50%. However, treatment with AT1-receptor antagonists did not influence binding of ATS to mesangial cells and subsequent complement activation indicating that the attenuated MCP-1 expression is not due to differences in delivery and binding of ATS to mesangial cells. CONCLUSION: Our data indicate that short-term antagonism of AT1 receptors abolished the early glomerular MCP-1 expression and M/M influx. These results indicate that angiotensin II may exert immunomodulatory effects in vivo and adds a new mechanism showing how this vasopeptide may be involved in the pathogenesis of renal diseases.     

Importance of proteins in the deterioration of the remnant kidneys, independently of other nutrients

Several experiments have shown that deterioration of renal parenchyma after reduction of functional mass is affected by the protein content of the diet. The respective role of proteins and that of other nutrients particularly phosphorus which varies with proteins was never clearly separated. Three groups of 9 uremic rats U I, U II, U III, received three diets differing exclusively in their protein content, which was supplied by casein and was respectively 8%, 16% and 32%. Other nutrients were maintained identical, including energy and minerals. Food intake was similar in U I and U II rats and was lower in U III rats. Mortality rate remained closely related to protein intake. Of U III rats, 78% died within 10 weeks and 100% within 15 weeks. Of U II rats, 56% were dead at week 15, and 100% at week 30. Mortality occurred significantly later in U I rats fed the lowest protein diet. Histology of remnant kidneys showed severe glomerular and tubular damage, with no or little calcium deposits despite normal phosphorus diet and frequent hyperphosphoremia. In conclusion, protein intake influences survival by accelerating the renal damage in rats with reduced kidney mass independently of any other nutrient.     

Expression of types I, II, and III TGF-beta receptors in human glomerulonephritis

Protein and mRNA expression of transforming growth factor-beta (TGF-beta) receptor type I (TbetaRI), type II (TbetaRII), and type III (TbetaRIII) were studied in serial sections of kidney samples obtained from patients with glomerulonephritis. In minimal change disease, weak expression of TbetaRI and TbetaRII was observed mainly in glomerular endothelial cells, peritubular capillaries, and interstitial arteriolar endothelial cells, whereas TbetaRIII expression was found mainly in the interstitium. Expression of all three TGF-beta receptors (TbetaR) was increased remarkably in glomerular and Bowman's capsular cells comprising the tuft adhesions to Bowman's capsules in glomerulonephritis with increased matrix accumulation, including IgA nephropathy, lupus nephritis, focal and segmental glomerulosclerosis, myeloperoxidase-antineutrophil cytoplasmic antibody-associated crescentic glomerulonephritis, and membranoproliferative glomerulonephritis. Increased expression of the three TbetaR was also seen in glomerular epithelial cells in the vicinity of glomerulosclerotic lesions, in crescent cells, and in some tubules and infiltrative mononuclear cells found in the periglomerular and tubulointerstitial lesions with increased matrix deposition. In contrast, no remarkable TbetaRII expression was noted in mesangial proliferative lesions in IgA nephropathy, lupus nephritis, and membranoproliferative glomerulonephritis. These data suggest that distinctive modulation of TbetaR expression may be involved in the development of adhesive, sclerotic, and proliferative renal lesions in human glomerulonephritis.     

Targeting TGF-beta overexpression in renal disease: maximizing the antifibrotic action of angiotensin II blockade

BACKGROUND: Overproduction of transforming growth factor-beta (TGF-beta) is a key mediator of extracellular matrix accumulation in fibrotic diseases. We hypothesized that the degree of reduction of pathological TGF-beta expression can be used as a novel index of the antifibrotic potential of angiotensin II (Ang II) blockade in renal disease. METHODS: One day after induction of Thy 1.1 glomerulonephritis, rats were treated with increasing doses of the Ang I converting enzyme (ACE) inhibitor enalapril and/or the Ang II receptor blocker losartan in the drinking water. Six days after disease induction the therapeutic effect on glomerular TGF-beta overexpression was evaluated. RESULTS: Both enalapril and losartan reduced TGF-beta overproduction in a dose-dependent manner, showing a moderate reduction at doses known to control blood pressure in renal forms of hypertension. A maximal reduction in TGF-beta expression of approximately 45% was seen for both drugs starting at 100 mg/liter enalapril and 500 mg/liter losartan, with no further reduction at doses of enalapril up to 1000 mg/liter or losartan up to 2500 mg/liter. Co-treatment with both drugs was not superior to single therapy. Consistent with our hypothesis that reduction in TGF-beta expression is a valid target, other disease measures, including glomerular matrix accumulation, glomerular production and mRNA expression of the matrix protein fibronectin and the protease inhibitor plasminogen-activator-inhibitor type 1 (PAI-1) closely followed TGF-beta expression. CONCLUSIONS: The data suggest that these therapies act through very similar pathways and that, in order to more effectively treat renal fibrosis, these drugs must be combined with other drugs that act by different mechanisms.     

Sairei-to inhibits the production of endothelin-1 by nephritic glomeruli(2): alisols, possible candidates as active compounds

We have previously reported that Sairei-to (TJ-114), a Japanese herbal medicine, prevented the production of endothelin-1 in anti-GBM nephritic rats, and that Alismatis Rhizoma (Takusha in Japanese), one of the twelve herbs composing TJ-114, might be responsible for the action. In order to further clarify the antinephritic components of TJ-114, we investigated the effects of Takusha extracts on various parameters, including endothelin-1 production of glomeruli in vitro and in vivo using anti-GBM nephritic rats. MeOH-100% MeOH and MeOH-50% MeOH fractions (31.3 microgram/ml or higher) strongly inhibited an increase in endothelin-1 concentration in culture medium when they were added to a culture of glomerular cells derived from nephritic rats. In addition, oral administration of the MeOH-100% MeOH fraction (30 mg/kg) ameliorated the proteinuria, increase in systolic blood pressure and changes in histopathological parameters in nephritic rats. Oral administration of the MeOH-100% MeOH fraction inhibited increase in endothelin-1 expression in the glomeruli of nephritic rats and in endothelin-1 production by a culture of glomerular cells derived from the nephritic rats. Alisols A and B, the main constituents of the MeOH-100% MeOH fraction, inhibited in vitro endothelin-1 production by glomerular cells derived from the nephritic rats. Oral administration of alisol B (30 mg/kg) prevented the endothelin-1 expression by glomeruli and the increase in endothelin-1 production by cultured nephritic glomerular cells. Oral administration of alisol B also ameliorated the proteinuria, the increase in systolic blood pressure and the changes in histopathological parameters in the nephritic rats. These results indicate that the antinephritic action of TJ-114, resulting from the inhibition of endothelin-1 production, may be attributed to the alisols in Takusha.     

Potential role of TGF-beta in diabetic nephropathy

Renal injury in diabetes mellitus is a major cause of morbidity and mortality. Several manifestations of diabetic nephropathy may be a consequence of altered production and/or response to cytokines or growth factors. Transforming growth factor-beta (TGF-beta) is one such factor because it promotes renal cell hypertrophy and regulates the production of extracellular matrix molecules. In addition, high ambient glucose increases TGF-beta1 mRNA and protein level in cultured proximal tubular cells and glomerular epithelial and mesangial cells. Neutralizing anti-TGF-beta antibodies or antisense TGF-beta1 oligodeoxynucleotides prevents the hypertrophic effects of high glucose and the stimulation of matrix synthesis in renal cells. Several reports have described overexpression of TGF-beta in the glomeruli and tubulointerstitium of experimental and human diabetes mellitus. We recently provided evidence that the kidney in diabetic patients displays net renal production of immunoreactive TGF-beta1, whereas there is net renal extraction in nondiabetic subjects. We also demonstrated that short-term treatment of streptozotocin-diabetic mice with neutralizing monoclonal antibody directed against TGF-beta significantly reduces kidney weight and glomerular hypertrophy, and attenuates the increase in extracellular matrix mRNA levels. The factors that mediate increased renal TGF-beta activity involve hyperglycemia per se and the intermediary action of other potent mediators such as angiotensin II, thromboxane, endothelins, and platelet-derived growth factor.     

Diet, overfeeding, and moderate dietary restriction in control Sprague-Dawley rats: II. Effects on age-related proliferative and degenerative lesions

This study compared the effects of ad libitum (AL) overfeeding and moderate dietary restriction (DR) of 2 different diets on Sprague-Dawley (SD) rat survival and spontaneous, age-related proliferative and degenerative lesions. SD rats were fed Purina Rodent Chow 5002 or a modified Rodent Chow 5002-9 containing lower protein, fat, metabolizable energy, and increased fiber by AL or by DR at 65% of the AL amount by measurement or time (6.5 hr). At 106 wk, rats fed the 5002-9 diet AL did not have significantly improved survival over rats fed the 5002 diet AL. The 5002 diet fed DR by time (6.5 hr) improved survival for males but not females. Only DR by measurement of both diets resulted in lower mortality for both sexes. By 106 wk rats fed either diet by AL had the same brain weights as DR fed rats, but AL fed rats had greater body weight, body fat content, and increased heart, lung, kidney, liver, adrenal, thyroid, and pituitary weights that correlated with an increased incidence and severity of degenerative and/or proliferative lesions in these organs. Moderate DR delayed the progression of chronic nephropathy by delaying the early development of glomerular hypertrophy that initiates the development of glomerular sclerosis and nephron loss in AL overfed rats. Moderate DR lowered the incidence, severity, and progression of cardiomyopathy and other degenerative, age-related lesions and appeared to delay the development of reproductive senescence in SD females. The conclusion from this study is that moderate DR delayed onset and progression of degenerative lesions, and death due to cardiovascular or renal disease, and thus potentially improves the bioassay to detect compound-specific chronic toxicity.     

Special Committee on HIV discusses AIDS, Committee goals

Intraperitoneal glucose tolerance tests were performed at 4-week intervals in groups of weanling rats before and after feeding with maize- or cassava-based diets with and without adequate protein and sublethal cyanide supplementation. Weaning weights were doubled (increase of about 50 g) after 4 weeks on control (maize-based with adequate protein) and protein-replete diets. Weight gain on the protein-deficient diets was much less (22 g or 50%), a pattern maintained by the rats on these diets until the age of 12 weeks. Plasma thiocyanate levels were identical at weaning and after 8 weeks of the control diet but increased by 200-300% after 4 weeks intake of the cassava or cyanide-supplemented feeds. Levels returned to normal in all groups after a further 4 weeks feeding with the control diet. Glucose tolerance (as assessed by the area under the 2 h glucose v. time curve) was impaired to a varying extent in the rats after 4 weeks on the various diets: protein-replete cassava and protein-deficient maize diets by 50% protein-deficient cassava diet by 300%, and cyanide-supplemented protein-deficient maize diet by 150%. The derangement in the rats on the protein-replete cassava diet was unaffected by a further 4 weeks intake of the control diet, unlike in the other groups where there was significant improvement in the glucose tolerance indices at the same time. It is concluded that in growing rats: (1) cassava intake and protein malnutrition may have independent and additive effects on the genesis of glucose intolerance, (2) cyanide supplementation of a cassava-free protein-replete diet has no effect on glucose tolerance.     

Angiotensin II participates in mononuclear cell recruitment in experimental immune complex nephritis through nuclear factor-kappa B activation and monocyte chemoattractant protein-1 synthesis

Angiotensin-converting enzyme (ACE) inhibitors reduce macrophage infiltration in several models of renal injury. We approached the hypothesis that angiotensin II (AngII) could be involved in inflammatory cell recruitment during renal damage through the synthesis of monocyte chemoattractant protein-1 (MCP-1). In a model of immune complex nephritis, we observed an up-regulation of renal MCP-1 (mRNA and protein) coincidentally with mononuclear cell infiltration that were markedly reduced by treatment with the ACE inhibitor quinapril. Exposure of cultured rat mesangial cells to AngII increased MCP-1 mRNA expression (2.7-fold) and synthesis (3-fold), similar to that observed with TNF-alpha. Since NF-kappaB is involved in the regulation of MCP-1 gene, we explored whether the effects of AngII were mediated through NF-kappaB activation. Untreated nephritic rats showed increased renal NF-kappaB activity (3.5-fold) that decreased in response to ACE inhibition. In mesangial cells, AngII activated NF-kappaB (4.3-fold), and the NF-kappaB inhibitor pyrrolidine dithiocarbamate abolished the AngII-induced NF-kappaB activation and MCP-1 gene expression. Our results suggest that AngII could participate in the recruitment of mononuclear cells through NF-kappaB activation and MCP-1 expression by renal cells. This could be a novel mechanism that might further explain the beneficial effects of ACE inhibitors in progressive renal diseases.     

Improved survival and amelioration of nephrotoxic nephritis in intercellular adhesion molecule-1 knockout mice

Intercellular adhesion molecule-1 (ICAM-1) expression is upregulated in nephrotoxic nephritis, a model of human rapidly progressive glomerulonephritis. To evaluate the pathogenetic relevance of ICAM-1 in this model, nephrotoxic nephritis was induced in ICAM-1 knockout mice and genetic controls. Mice were preimmunized with rabbit IgG in complete Freund's adjuvant. Seven days later they received rabbit anti-mouse glomerular basement membrane IgG. The early humoral immune responses (levels of circulating mouse anti-rabbit IgG, glomerular deposition of rabbit and mouse IgG and mouse C3c) were not altered in ICAM-1 knockout mice. During 28 d of follow-up, 3 of 19 control nephritic mice and 0 of 16 ICAM-1 knockout mice died. Proteinuria was high in nephritic control mice (means 10 to 12 mg/24 h at all time points investigated) and significantly reduced in nephritic ICAM-1 knockout mice (means <4.4 mg). Mean serum creatinine rose from 29 micromol/L at day -7 to 48 micromol/L (day 28) in nephritic control mice. This increase in serum creatinine was significantly lower in ICAM-1 knockout mice: 27 (day -7) and 36 micromol/L (day 28). Histologic analysis at day 28 revealed that ICAM-1 deficiency in nephrotoxic nephritis mice led to significantly reduced glomerular crescent formation (2+/-3% in ICAM-1 knockout mice versus 13+/-8% in nephritic controls) and tubulointerstitial injury (score 0.4+/-0.4 versus 2.0+/-1.1). By immunohistochemistry, ICAM-1 deficiency in nephritic mice led to significantly reduced (peri-)glomerular and/or interstitial macrophage influx, alpha-smooth muscle actin expression, and type IV collagen accumulation. These data indicate that ICAM-1 is a central mediator of glomerular and tubulointerstitial injury in murine nephrotoxic nephritis.     

Reproducibility of drug efficacy predictions by Holter monitoring in the electrophysiologic study versus electrocardiographic monitoring (ESVEM) trial. ESVEM Investigators

The effect of a newly developed free radical scavenger (OPC-15161) on the progression of nephrotoxic serum (NTS) nephritis was evaluated. NTS nephritis rats were sacrificed immediately before and 1, 2, 3, 6, and 24 h and 13 and 19 days after intravenous injection of NTS. The tissue content of phosphatidylcholine hydroperoxide, the activity of superoxide, the activity of superoxide dismutase in the renal cortex, and the serum malondialdehyde levels were measured. The phosphatidylcholine hydroperoxide content in the renal cortex of OPC-15161-treated NTS nephritis rats was lower than that in the control rats 24 h after NTS injection. The activity of superoxide dismutase in OPC-15161-treated rats was sustained in contrast to the decrease in this activity in the control rats 6 h after injection of NTS. The effects of OPC-15161, dipyridamole, and prednisolone on NTS nephritis rats were investigated. OPC-15161 (20 mg/kg p.o.) showed a potent inhibitory effect on the urinary protein excretion, whereas dipyridamole (30 and 100 mg/kg p.o.) and prednisolone (2 mg/kg p.o.) had less suppressive effects. In view of these results, we conclude that OPC-15161 notably ameliorated the urinary protein excretion by way of the suppression of lipid peroxidation in the renal tissue of NTS nephritis rats.     

Three-dimensional triple-quantum-filtered 23Na imaging of the dog head in vivo

Uninephrectomized rats with diet-induced hypercholesterolemia develop interstitial inflammation and fibrosis after 8 to 12 weeks. Fibrosis has been associated with the accumulation of lipid peroxidation products within the tubulointerstitium, along with increased renal mRNA levels for transforming growth factor beta-1 (TCF-beta 1), some matrix proteins, and the tissue inhibitor of metalloproteinases (TIMP-1). However, mRNA levels for urokinase-type plasminogen activator (uPA) have been found to be decreased. The purpose of the present study was to determine whether antioxidant therapy could attenuate interstitial fibrosis in hypercholesterolemic rats and to determine changes in the pattern of renal gene expression induced by antioxidant therapy. Three groups of uninephrectomized rats were studied after 12 weeks of feeding standard rat chow, an atherogenic diet (standard chow plus 4% cholesterol/1% cholic acid), or an atherogenic diet supplemented with high doses of the antioxidants probucol and vitamin E. Rats fed the atherogenic diet developed hypercholesterolemia and a 56% increase in total kidney collagen compared with rats fed standard chow. In comparison, the hypercholesterolemic rats treated with antioxidants had normal levels of renal lipid peroxidation products and a normal kidney collagen content. In contrast, there were no significant differences in urinary albumin excretion rates or the number of interstitial macrophages between the two hypercholesterolemic groups. Compared with the untreated hypercholesterolemic group, antioxidant therapy induced significant reductions in renal mRNA levels for procollagen III (to 60% of untreated levels), collagen IV (60%), and TIMP-1 (20%), while uPA levels were significantly increased (to 210%). Paradoxically, antioxidant therapy was associated with a significant increase in renal TGF-beta 1 mRNA levels (to 150%), although TGF-beta 1 protein expression shifted from interstitial to tubular epithelial cells in predominance. The results of the present study demonstrate the efficiency of antioxidant therapy in preventing renal interstitial fibrosis in hypercholesterolemic rats with a single kidney. Based on changes in renal gene expression at the mRNA level, impaired matrix protein synthesis and increased intrarenal activity of the metalloproteinases and uPA/plasmin may play a role in the attenuation of fibrosis.     

Effects of zinc deficiency on endogenous antioxidant enzymes and lipid peroxidation in glomerular cells of normal and five-sixths nephrectomized rats

We evaluated the effects of zinc deficiency on the activities of endogenous antioxidant enzymes and lipid peroxidation in rat glomerular cells (GCs). Male Sprague-Dawley rats (n = 48) were fed a zinc-deficient diet and deionized distilled water for 1 week to induce zinc deficiency. Half of the rats (zinc-deficient group) continued on this diet for 4 weeks, and the other half (zinc-replete group) were maintained on the same diet but with zinc-supplemented water (150 mg/Lzinc sulfate solution). Half of each group underwent five-sixths nephrectomy, while the other half underwent a sham operation. Another 12 normal rats (controls) were fed standard rat chow (containing 23.4% protein and 70 ppm zinc) and drank deionized distilled water. The zinc-deficient rats, including sham and five-sixths nephrectomized rats, showed severe growth retardation and poor appetite. Their mean plasma zinc concentrations were half that of normal control rats, but their plasma copper concentration was significantly higher than that of the control rats. Zinc supplementation corrected the abnormality of plasma zinc and copper concentrations and the loss of body weight in zinc-deficient rats. Zinc-deficient rats exhibited lower renal creatinine clearance and higher GC-malondialdehyde (GC-MDA) than zinc-replete rats. The remnant kidney of all five-sixths nephrectomized rats, including zinc-deficient and zinc-replete rats, showed a compensatory elevation in renal creatinine clearance and increased GC-MDA concentrations. Zinc concentrations in the renal cortex were decreased in zinc-deficient rats and the activities of GC-superoxide dismutase and GC-glutathione peroxidase were increased, while zinc-replete rats exhibited normal activities of GC-superoxide dismutase and GC-glutathione peroxidase. We suggest that zinc deficiency enhances the formation of reactive oxygen species but does not affect the activities of endogenous antioxidant enzymes in glomerular cells.     

Effect of protein-induced calciuria on calcium metabolism and bone status in adult rats

45Ca-labeled adult male rats were fed diets high in protein to determine long-term effects on calcium metabolism and bone status. Factors influencing renal excretion of calcium were examined for their involvement in protein-induced hypercalciuria. Control rats were fed a 6% casein diet. Test diets contained 6% casein plus 24% protein as lactalbumin, beef, casein, soy, egg white or gelatin. All diets were equal in Mg, P, and Ca. Collections made during the 20-week feeding regimen indicated a transient but marked calciuria (greater than or equal to 200% of control) occurring at or prior to days 56-59 by rats fed the lactalbumin, egg white, gelatin (P less than or equal to 0.001) and 30% casein (P less than or equal 0.01) diets. Soy and beef diets were not calciuric. At days 56-59, rats fed lactalbumin, 30% casein, soy and egg white exhibited significantly depressed urinary specific activity of calcium (P less than or equal to 0.001), and all rats fed test diets produced higher fecal endogenous calcium, suggesting an increased absorption. No compositional differences indicative of bone resorption were present in the femur or mandibles of any rat fed test protein, dismissing bone as the source of calciuria. End-products of protein metabolism known to chelate calcium or compete with its renal reabsorption were significantly correlated with urinary calcium; these included sulfate, oxalate and sodium.