Determination of renal porphyrin handling in rats suffering from different kinds of chronic renal failure (CRF): Uranyl nitrate (UN) induced fibrosis or 5/6-nephrectomy (5/6NX)

The renal handling of porphyrins is reported to be a sensitive marker for chronic renal failure (CRF) for two reasons: heme is synthesised in proximal tubules and porphyrins are reabsorbed in the renal proximal tubule by apical peptide transporter PEPT 2. Two different models of CRF in female Wistar rats have been used for investigation of renal porphyrin handling: (1) single administration of uranyl nitrate (UN; 0.5 mg/100 g b.wt.) and (2) 5/6 nephrectomy (5/6NX). Renal clearance experiments were performed at weeks 2 and 10 after the onset of CRF. The concentrations of porphyrin intermediates (uroporphyrin I and III, coproporphyrin I and III, heptaporphyrin, and pentaporphyrin) were measured by HPLC with fluorescence detection.

Both after UN and 5/6NX a significant reduction of body weight occurred. The kidney weight was enhanced 2 weeks after UN compared to controls (+31%). After 5/6NX, the weight of the remnant kidney was 44% (2^nd week) and 140% (10^th week) higher compared to one control kidney.

Urine volumes and GFR were significantly reduced at week 2 and 10 after 5/6NX, but at week 10 after UN values were comparable to controls.

Two weeks after UN and 5/6NX the concentrations of heptaporphyrin was moderately decreased in renal tissue whereas after 10 weeks the concentrations of most porphyrins were increased in the kidney. The plasma levels of free porphyrins were only slightly enhanced (week 2). The renal excretion of porphyrins was initially slightly reduced in both models, whereas it increases 10 weeks after UN, but it remained reduced 10 weeks after 5/6NX.

UN induces tubulointerstitial fibrosis including atrophic glomeruli, whereas 5/6NX was characterized by distinct proteinuria, dilated tubules containing hyaline casts. A modulation of porphyrin metabolism in the kidney seems first of all to be responsible for UN effect on renal porphyrin handling. Summing up the 5/6NX results, both reduction in intact renal tissue mass and a modification of enzymes involved in heme biosynthesis by uraemic toxins are responsible for accumulation of porphyrins in renal tissue. After 5/6NX reduced excretion of porphyrins into urine and enhanced porphyrin concentrations in the kidney indicate more a damage of renal porphyrin biosynthesis than changes in their reabsorption.     

Temporary warm ischaemia, 5/6 nephrectomy and single uranyl nitrate administration--comparison of three models intended to cause renal fibrosis in rats.

In patients the progression of pathologic renal processes after the treatment of primary disease is a problem of increasing importance and therapeutic strategies are insufficient till now. The aim of this paper was to search for rat models of interstitial fibrosis as a basis for testing therapeutic strategies to prevent end-stage renal failure. Experiments were done on adult female Wistar rats (Han:Wist) to investigate long-term consequences of temporary warm ischaemia, 5/6 nephrectomy (5/6 NX) and single uranyl nitrate (UN) administration (0.3 or 0.5 mg/ 100 g body wt. intraperitoneally). Observation time was 20 weeks after injury in each group. Creatinine clearance, urinary protein excretion and hydroxy-proline (OH-proline) concentration in renal tissue were measured and light microscopic investigations were done to characterise both quality and time course of long-term renal damage in relation to matched control animals. Temporary warm ischaemia and 5/6 NX did not cause any fibrotic changes during the 20 weeks observation period. The higher UN dose led to decreased creatinine clearance, increased urinary protein excretion and enhanced OH-proline concentration in renal tissue. Morphologic investigations showed fibrotic areas containing strongly dilated and atrophic tubules with thickened basal membranes. These effects can be seen from week four after UN administration up to the end of the observation period. In conclusion, administration of one single dose of UN is a simple procedure to induce interstitial renal fibrosis as an experimental model to investigate therapeutic strategies for their prevention.     

Use of gene chip technology for the characterisation of the regulation of renal transport processes and of nephrotoxicity in rats

Gene expression profiling using microarrays (rat-specific array RG-U34A, Affymetrix, U.S.A.) was employed for the investigation of: (1) hormonal regulation of renal function and (2) nephrotoxicity. For this purpose about 8,800 genes were analysed in kidney and, additionally, in liver tissue.

Ad 1.) Kidney functions develop during postnatal life. Thus, in vivo transport and accumulation of p-aminohippurate (PAH) was investigated on renal cortical slices (RCS) from 10- and 55-day-old rats. The animals were treated with dexamethasone (DEXA; 60 μg/100 g b.wt./day) for 3 days, which caused a significant reduction in the accumulation of PAH in 10-day-old rats (42 ± 5% whereas it was only slightly reduced in 55-day-old rats (70 ± 8%). To further clarify the regulation of renal function by DEXA, results were compared with those obtained previously after in vitro stimulation with DEXA. RCS were incubated for 24 hours in DEXA-containing medium (10⁻⁹ M). Under these conditions DEXA significantly increased the PAH uptake capacity in RCS obtained from 10- and 55-day-old rats up to 126 and 136%, respectively. Thus a stimulation of tubular transport capacity is possible in vitro. The effect of DEXA treatment on the gene expression of the kidney (in vivo) was moderate. Focussing especially on transporters, ion channels, ATPases, glucuronyltransferases, glutathione-S-transferase and cytochrome P450, the expression of only few genes were significantly changed (3 to 50-fold up- or down-regulation). Moreover, distinct age differences were found after in vivo administration of DEXA. The investigation of in vitro effects of DEXA is currently been performed.

Ad 2.) The kidney is threatened by nephrotoxins because of its ability to accumulate them. We used a single administration of uranyl nitrate (UN; 0.5 mg/100 g b.wt.) as a model for chronic renal failure (CRF). Clearance experiments were performed 10 weeks after UN administration (maximal symptoms of CRF) in adult female rats. As expected, UN induced interstitial cicatrices with reduced GFR and diminished PAH transport capacity. Despite the impressive morphological and functional changes in the kidney after exposure to UN, the gene expression profiles in the kidneys were only minimally affected: we found significantly changed expression levels for only 20 genes (5 genes were up-regulated [e.g. transgelin], 15 down-regulated [among these the Na-K-Cl-symporter, insulin-like growth factor, kallikrein, and ornithine decarboxylase). The lack of agreement between gene expression data and the nephrotoxic effects of UN can probably be explained by the long time interval between dosing and the assessment of the effect. The results confirm that primary genomic responses are likely to be strongest transiently after exposure and then decrease in intensity.     

Ultrastructural and ultraimmunohistochemical changes upon partial nephrectomy and uranyl intoxication in the rat kidney

We studied kidneys of rats intoxicated with uranylnitrate (UN) or subjected to 5/6 nephrectomy (NX) or after a combination of both procedures (NX–UN). Our observations indicate that UN causes impressive changes of ultrastructure (partial loss of brush border, appearance of intercellular clefts in the epithelial barrier) and altered protein expression (α-SMA, collagen I and III) in proximal tubule cells. Renal parameters (creatinine clearance, proteinuria) seemed to be unaffected. Blood pressure recovered to normal values within 12 months. However ultrastructural and functional restoration of modified proximal tubules was not complete. We conclude that changed proximal tubules may induce progression of interstitial fibrosis causing renal failure. NX animals and more pronounced NX–UN animals showed dramatic changes in renal function. We observed increased levels of proteinuria, blood pressure and decreased creatinine clearance. Progressive glomerular reorganization includes loss of filtration gaps and enhanced thickness of glomerular basement membranes (GBM) with increased immunoreactivity for collagen IV. Cells in vicinity of Bowman's capsule contained high amounts of immunoreactive α-smooth muscle actin. The NX–UN group showed more dramatic changes in ultrastructure of proximal tubules including apoptosis. Enhanced expression and secretion of extracellular matrix proteins (ECM e.g. collagens I, III, fibronectin) indicate progressive epithelial–mesenchymal transition (EMT) leading to permanent impairment of renal function.     

Effect of AT1 angiotensin receptor antagonist on lipid peroxidation and antioxidative defense in diabetic kidney

The effects of losartan potassium, an AT₁ angiotensin receptor antagonist on lipid peroxidation and activities of superoxide dismutase and catalase in the kidney of streptozotocin-diabetic rats were studied. Experimental diabetes resulted in an increase of malondialdehyde content of the kidneys and decreases of superoxide dismutase and catalase activity in this organ after 6 and 12 weeks. Administration of losartan potassium (1 mg/kg body weight in the drinking water) prevented the increase on malondialdehyde level and normalized the activities of antioxidant enzymes after both 6 and 12 weeks of the experiment. These results demonstrate an antioxidative effect of losartan potassium in diabetic rats in vivo.     

Ascorbic acid metabolism in rats and guinea pigs after the administration of ethanol

Ascorbic acid metabolism was studied in guinea pigs and rats after the administration of ethanol and a high dose of ascorbic acid (AA). Male guinea pigs were maintained for 30 days as follows: (1) controls (1 mg AA/100 g body wt.); (2) ethanol (1 mg AA/100 g body wt. + 900 mg ethanol/100 g body wt); (3) ascorbic acid (25 mg AA/100 g body wt.); (4) ascorbic acid + ethanol (25 mg AA/100 g body wt. + 900 mg ethanol/100 g body wt.). Rats were also grouped into four groups as in the case of guinea pigs, but the dose of AA was 200 mg/100 g body weight. Rats adjusted to ethanol intoxication by enhancing the biosynthesis of ascorbate as evidenced by elevated activity of L-gulono lactone oxidase (GLO). Hence ascorbate levels were not lowered in rats after administration of alcohol. However, alcohol administration lowered tissue levels of ascorbate in guinea pigs. But the supplementation of ascorbate along with alcohol raised the tissue level of this vitamin. Guinea pigs responded to the ascorbate deficiency during alcohol administration by lowering the degradation of ascorbate, as seen by the lower activity of the degrading enzyme gulono lactone hydrolase. It is concluded that on the administration of alcohol, guinea pigs are dependent upon additional exogenous supplies of ascorbic acid, whereas rats are not.     

Renal interstitial fibrosis (RIF): II. Ultrasound follow up study of single uranyl nitrate administration causing renal dysfunction in rats – comparison with histologic and functional renal parameters

A single administration of uranyl nitrate (UN; 0.5 mg/100 g b. wt. i.p.) to adult female Wistar rats reliably induces renal interstitial fibrosis (RIF) providing an experimental model to investigate therapeutic strategies. It was the aim of this study to further characterise a rat model of UN induced RIF which we have studied previously (APPENROTH et al. 2001) by the comparison of functional parameters with ultrasonographic examination over a period of 30 weeks after injury. In the acute phase after UN administration (between days 2 and 17) signs of inflammation (increase in renal blood flow, swelling of renal cortex, enlargement of renal pelvis) could be detected by ultrasound. After four weeks UN led to functional changes (decreased creatinine clearance, increased urinary protein excretion and increased OH-proline concentration in renal tissue). In vitro, the accumulation of p-aminohippurate and the gluconeogenesis were reduced. In accordance with the functional changes, distinct ultrasonographic abnormalities could be seen between weeks 10 and 30 after UN with regard to changes in kidney size and shape, reduced renal perfusion and enlargement of renal pelvis. The sensitivity of ultrasonography in small laboratory animals is limited and most useful for follow-up studies of acute renal changes after administration of nephrotoxins. Ultrasonography can not be recommended for non-invasive screening of the progression of chronic renal failure.     

The role of angiotensin II in the feedback control of renin gene expression

 This study aimed to characterize the influence of endogenous angiotensin II on renal renin gene expression during different states of a stimulated and of a suppressed renin system. To this end the renin system in male Sprague Dawley rats was stimulated by unilateral renal artery clipping (0.2 mm clip), by furosemide (60 mg/kg per diem) or isoproterenol (160 μg/kg per diem), and by ingestion of a low-salt diet (0.02%), or was suppressed by setting a contralateral renal artery clip (0.2-mm clip) or by ingestion of a high-salt diet (4%). During the last 2 days of these different treatment regimens, the animals were treated with the angiotensin II AT1 receptor antagonist losartan (40 mg/kg per diem) and renal renin mRNA levels were assayed. Renin gene expression was stimulated four- to fivefold by renal artery clipping and isoproterenol infusion, two- to threefold by furosemide and a low-salt diet, and about fourfold by losartan. Additional treatment with losartan potentiated the stimulatory effects of a low-salt diet, of furosemide and of isoproterenol infusion on renin gene expression, whilst there was no significant additional effect of losartan on renin gene expression in clipped kidneys. Both contralateral renal artery clipping and a high-salt diet decreased renin mRNA levels to about 50% of the control value. In rats with a unilateral clip, additional losartan treatment caused renin mRNA to increase to about 350% of the control value in the contralateral kidney but to only 110% of the control value in animals on a high-salt diet. These findings suggest that the enhanced formation of angiotensin II during a low-salt intake, during tubular inhibition of salt reabsorption or during β-adrenoreceptor activation plays a relevant negative feedback role in the activation of the renin gene. Moreover, in rats with one hypoperfused kidney, angiotensin II could be involved in the inhibition of renin gene expression in the contralateral kidney. In hypoperfused kidneys, however, and in animals on a high-salt diet, angiotensin II appears to play only a minor feedback role in the regulation of the renin gene. Received: 10 September 1996 / Received after revision: 17 February 1997 / Accepted: 25 February 1997     

Renal interstitial fibrosis (RIF): II. Ultrasound follow up study of single uranyl nitrate administration causing renal dysfunction in rats--comparison with histologic and functional renal parameters.

A single administration of uranyl nitrate (UN; 0.5 mg/100 g b. wt. i.p.) to adult female Wistar rats reliably induces renal interstitial fibrosis (RIF) providing an experimental model to investigate therapeutic strategies. It was the aim of this study to further characterise a rat model of UN induced RIF which we have studied previously (Appenroth et al. 2001) by the comparison of functional parameters with ultrasonographic examination over a period of 30 weeks after injury. In the acute phase after UN administration (between days 2 and 17) signs of inflammation (increase in renal blood flow, swelling of renal cortex, enlargement of renal pelvis) could be detected by ultrasound. After four weeks UN led to functional changes (decreased creatinine clearance, increased urinary protein excretion and increased OH-proline concentration in renal tissue). In vitro, the accumulation of p-aminohippurate and the gluconeogenesis were reduced. In accordance with the functional changes, distinct ultrasonographic abnormalities could be seen between weeks 10 and 30 after UN with regard to changes in kidney size and shape, reduced renal perfusion and enlargement of renal pelvis. The sensitivity of ultrasonography in small laboratory animals is limited and most useful for follow-up studies of acute renal changes after administration of nephrotoxins. Ultrasonography can not be recommended for non-invasive screening of the progression of chronic renal failure.     

Influence of sympathetic and AT1‐receptor blockade on angiotensin II and adrenergic agonist‐induced renal vasoconstrictions in spontaneously hypertensive rats

Aim: This study investigated the influence of angiotensin II (Ang II) receptor and adrenergic blockade on the renal vasoconstrictions caused by Ang II and adrenergic agonists in spontaneously hypertensive rats (SHR). Methods: Forty‐eight SHR were subjected to 7 days of losartan (10 mg kg^?1 day^?1 p.o.), carvedilol (5 mg kg^?1 day^?1 p.o.) or losartan + carvedilol (10 mg kg^?1 day^?1 + 5 mg kg^?1 day^?1 p.o.). On day 8, the rats were anaesthetized and renal vasoconstrictor experiments performed. One group of rats underwent acute unilateral renal denervation. Results: There were significant (P < 0.05) reductions in the renal vasoconstrictor responses to noradrenaline, phenylephrine, methoxamine and Ang II after losartan and carvedilol treatments compared with that in untreated rats (all P < 0.05). However, in renally denervated SHR treated with carvedilol, the vasoconstrictor responses to all the vasoactive agents were enhanced compared with those in SHR with intact renal nerves treated with carvedilol. Intact SHR given both losartan and carvedilol showed greater renal vasoconstrictor responses to the vasoactive agents than when given either losartan or carvedilol alone (all P < 0.05). Conclusion: Carvedilol reduced the vasoconstrictor response to Ang II and all the adrenergic agonists in the presence of the renal nerves, but, following the removal of renal sympathetic activity, carvedilol enhanced the sensitivity of both renal α₁‐adrenoceptors and AT₁ receptors to the vasoactive agents. Co‐treatment with losartan and carvedilol reduced the renal vasoconstrictor responses to exogenously administered vasoactive agents but to a lesser extent than losartan or carvedilol alone. The results obtained demonstrate an interaction between Ang II receptors and adrenergic neurotransmission in the SHR.     

Suitability of 5/6 nephrectomy (5/6NX) for the induction of interstitial renal fibrosis in rats – Influence of sex, strain, and surgical procedure

Chronic renal failure (CRF) is a serious clinical problem and currently there are no adequate therapeutic strategies for treatment. Many possible treatment strategies have been tested in rats with CRF induced by subtotal nephrectomy. However, reports in the literature concerning the consequences of this procedure on rat kidney function are contradictory. For instance, such an intervention in male Sprague-Dawley rats apparently initiates the development of interstitial renal fibrosis, while in our similar studies on female Wistar rats (HW) there was minimal renal fibrosis. Therefore, we carried out experiments in adult rats to investigate the long-term consequences of 5/6 nephrectomy (5/6NX) in relation to (1) sex, (2) strain, and (3) two methods of surgical ablation. Ten weeks after 5/6NX, body weight gain, systolic blood pressure, creatinine clearance, and urinary protein were measured, along with renal hydroxyproline concentration determinations to assess the deposition of extracellular matrix. Also, light microscopic investigations were done to characterize renal damage. The functional parameters clearly indicated the development of CRF, while morphologic investigations showed only moderate fibrotic areas containing atrophic tubules and lymphocytic infiltrates. However, 45-60% of glomeruli were sclerotic. In summary, 5/6NX, using either method of partial nephrectomy, induces signs of moderate glomerulonephritis preferentially in female HW rats. Thus 5/6NX in female HW rats can be recommended as a suitable model in the induction of renal fibrosis.     

Changes in angiotensin converting enzyme activity in the renal vascular bed of streptozotocin-induced diabetic rat

The purpose of this study was to look for evidence of changes in angiotensin converting enzyme activity in the renal vascular bed of streptozotocin (STZ)-induced diabetic rats. To assess the activity of the enzyme, we examined angiotensin I- and angiotensin II-induced vasoconstriction in perfused kidneys from controls and diabetic rats. Angiotensin I (3x10(-9) to 3x10(-6) M) induced a dose-dependent vasoconstriction in control kidneys; this response was completely inhibited by losartan (10(-5) M) and markedly inhibited by both captopril (10(-4) M) and indomethacin (10(-5) M). Angiotensin II (10(-10) to 3x10(-7) M) also caused a dose-dependent vasoconstriction in control kidneys; this response was markedly enhanced by 10(-4) M L-NNA, and significantly inhibited by losartan (10(-5) M). Angiotensin I-induced vasoconstriction was slightly greater in STZ-induced diabetic rats than in controls, but the maximal response was unaffected. These results suggest that angiotensin I is rapidly converted to angiotensin II in the renal vascular bed, and that converting enzyme activity in the renal vascular bed may be decreased in STZ-induced diabetic rats.     

Effect of losartan on sodium appetite of hypothyroid rats subjected to water and sodium depletion and water, sodium and food deprivation

The involvement of angiotensin AT1 receptors in sodium appetite was studied in hypothyroid rats treated with the angiotensin II antagonist losartan. Losartan was administered chronically by the oral route or acutely by the subcutaneous route after water and sodium depletion or water, sodium and food deprivation. Three days after addition of losartan to the food at the dose of 1.0 mg x g(-1), the rats significantly reduced (P < 0.02) their spontaneous intake of 1.8% NaCl. Increasing the dose of losartan to 2.0 and 4.0 mg x g(-1) did not reduce NaCl intake; in contrast, the intensity of the sodium appetite gradually returned to previous levels. The simultaneous administration of captopril, an angiotensin converting enzyme inhibitor, and losartan significantly increased (P < 0.05) NaCl intake and after captopril removal NaCl intake returned to the levels observed with losartan treatment alone. The administration of losartan 4 days after the beginning of captopril treatment significantly reduced (P < 0.0001) NaCl intake. Following acute administration of losartan, water- and sodium-depleted rats significantly reduced their NaCl and water intake (P < 0.001). The administration of losartan also induced a significant reduction in NaCl and water intake in water, NaCl and food-deprived rats (P < 0.0001 and P < 0.001, respectively). The present results show that chronic treatment with oral losartan inhibited spontaneous sodium appetite in hypothyroid rats. Continuation of treatment rendered rats resistant to the blockade of AT1 receptors. Water and sodium depletion and water, NaCl and food deprivation induced sodium appetite, which in the short term depends on cerebral angiotensinergic activity mediated by the activation of AT1 receptors.     

Differential anxiolytic effect of enalapril and losartan in normotensive and renal hypertensive rats

The effect of angiotensin-converting enzyme (ACE) inhibitor enalapril (EPL) (2 and 4 mg/kg), angiotensin (AT) II receptor antagonist losartan (LRN) (5 and 10 mg/kg), and anxiolytic drug diazepam (DZP) (0.5 mg/kg) on anxiety parameters were evaluated in experimentally induced renal hypertensive rats (RHR). Renal hypertension was induced in Wistar strain male albino rats weighing 200-250 g by following the method of Goldblatt. The animals having systolic blood pressure more than 180-210 mm Hg were subjected to open-field exploratory behaviour, elevated plus maze behaviour, and social interaction tests of anxiety. The RHR showed hyperactivity in open-field behaviour and anxiogenicity in elevated plus maze and social interaction tests. Losartan (5 and 10 mg/kg) and DZP (0.5 mg/kg) significantly attenuated the hyperactivity and anxiogenic behaviour in experimentally induced hypertensive rats and induced anxiolysis in normotensive rats (NTR). Enalapril reversed the hypertension-induced alteration only at higher dose (4 mg/kg) and failed to show any effect in NTR. It can be concluded that renin angiotensin aldosterone system (RAAS) has a significant role on behaviour, and LRN has shown better effect in reversing the hyperactivity and anxiogenicity in the experimentally induced hypertensive rats, indicating a possible role of AT receptor in the mediation of anxiolysis.     

Renin-angiotensin system in stroke-prone spontaneously hypertensive rats.

The development of malignant hypertension was studied in stroke-prone spontaneously hypertensive rats (SHR) kept on 1% NaCl as drinking water. Along with salt-loading, blood pressure gradually increased and reached a severe hypertensive level (greater than 230 mmHg), which was followed by increases in urinary protein (greater than 100 (mg/250 g body wt)/day) and plasma renin concentration (PRC, from 18.9 +/- 0.1 to 51.2 +/- 19.4 (ng/ml)/h, mean +/- SD). At this stage, renal small arteries and arterioles showed severe sclerosis and fibrinoid necrosis. Stroke was observed within a week after the onset of these renal abnormalities. The dose of exogenous angiotensin II (AII) producing 30 mmHg rise in blood pressure increased with the elevation of PRC, from 22 +/- 12 to 75 +/- 36 ng/kg, which was comparable to that in rats on water. The fall of blood pressure due to an AII inhibitor, [1-sarcosine, 8-alanine]AII (10(microgram/kg)/min for 40 min) became more prominent with the increase in PRC in salt-loaded rats, but was not detected in rats on water. These findings suggest that the activation of renin-angiotensin system participates in malignant hypertension of salt-loaded stroke-prone SHR rats that show stroke signs, proteinuria, hyperreninemia, and renovascular changes.     

血管紧张素Ⅱ刺激高草酸尿症大鼠肾脏NADPH氧化酶的表达

目的： 观察肾素-血管紧张素系统（RAS）和NADPH氧化酶在高草酸尿症大鼠肾脏氧化应激（OS）形成中的相互作用。方法: 采用0.8%乙二醇饮水法诱导建立高草酸尿症大鼠模型。动物分6个组（n=8）,A组:空白组;B组：高草酸尿症组;C组：高草酸尿症+apocynin治疗组;D组：单纯apocynin治疗组;E组：高草酸尿症+losartan治疗组;F组：单纯losartan治疗组。后4组分别灌胃给予apocynin（0.2 g·kg-1·d-1）或losartan（30 mg·kg-1·d-1）。4周后检测大鼠尿液、肾组织中的OS指标（尿8-IP和肾组织SOD活性）,放免法检测肾组织血管紧张素Ⅱ（AngⅡ）的含量,免疫组化法观察NADPH氧化酶亚单位P47phox蛋白在肾脏中的表达位置,RT-PCR法检测肾组织p47phox mRNA的表达水平。结果: p47phox在各组大鼠肾脏中都有广泛表达,表达部位包括肾皮质、内髓、外髓。与A组比较,B组尿液8-IP明显增多,肾组织SOD活性降低,肾组织AngⅡ含量增多,p47phox mRNA在肾组织中的表达水平也明显增多。使用apocynin（C组）和losartan（E组）均可抑制肾组织p47phox mRNA的表达,同时肾脏的OS程度减轻。结论: 在高草酸尿症大鼠模型中,肾脏p47phox mRNA表达增多,导致肾脏OS;同时肾脏RAS也被激活,后者可通过刺激p47phox mRNA的表达而促进肾脏OS程度增加。     

Development of renal potassium excretion capacity in the neonatal rat

We investigated the capacity of newborn rats to excrete an acute potassium load to understand the development of a renal potassium excretion system. Three groups of the rats (7-14 d) were used to collect urine periodically over 6 h after oral infusion of potassium: control (no potassium loading) and low- and high-potassium-loaded rats. In the low-potassium-loaded group, infused with about 0.6 microEq of potassium chloride/g body wt., the rate of renal potassium excretion increased from 0.08 plus minus 0.02 (7 d) to 0.13 plus minus 0.02 (10 d) and 0.21 plus minus 0.03 (14 d) microEq/h/g body wt. The high-potassium-loaded rats (1.5-2.8 microEq/g body wt. potassium load) excreted potassium at a higher rate of 0.18 +/- 0.05 (7 d), 0.30 +/- 0.02 (10 d), and 0.45 +/- 0.10 (14 d) microEq/h/g body wt. They excreted 77% (7 d), 76% (10 d), and 95% (14 d) of the potassium load. These values were much larger than the rate of 0.026 microEq/h/g body wt. of the control rats and of 0.08 microEq/h/g body wt., a mean potassium excretion rate during development from 7 to 14 d calculated from the data in the previous study (Kanno T et al.: J. Pediatr. Gastr. Nutr. 24: 242-252, 1997). In the same period, serum potassium concentration in the newborn rats decreased significantly (p < 0.01) from 7.2 +/- 0.1 (7 d) to 6.7 +/- 0.1 mEq/l (14 d). All these results suggest that a renal potassium excretion system in the rat develops at least in the second week of life, and its capacity is high enough to excrete the daily potassium intake.     

Relationship between adrenal steroids and renal Na−K-ATPase

Mineralo- and glucocorticoids stimulate renal Na–K-ATPase activity if given over a few days, but their immediate effect on the enzyme (i.e. within the time period required to alter electrolyte transport) remains controversial. We evaluated the short-term (3 h) in vivo effect of physiologic and pharmacologic doses of the natural glucocorticoid (corticosterone) and mineralocorticoid (aldosterone), and of a semisynthetic glucocorticoid (dexamethasone) on Na–K-ATPase activity in cortical collecting tubules microdissected from adrenalectomized rats. This nephron segment was chosen because it is a major target site for both classes of corticoids. Neither corticosterone (0.006, 0.6, and 5 mg/100 g body wt, IM), nor dexamethasone (5 mg/100 g body wt, IM) or aldosterone (10 g and 50 g, IV) altered significantly Na–K-ATPase activity in the cortical collecting tubule of these animals 3 h after administration. These results confirm our previous observations in the mouse, and suggest that the enhancing effect of corticosteroids on the renal enzyme seen after longer intervals represents a secondary phenomenon, possibly related to augmentation of the sodium load presented to the pump.     

Influence of epidermal growth factor (EGF) on renal transport of PAH and amino acids in amino acid loaded rats.

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal transport of p-amino-hippurate (PAH), electrolytes, and amino acids was investigated. After loading with PAH (200 mg/100 g b.wt. iv.), PAH excretion in EGF treated rats (8 microg/100 g b.wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was increased by about 20 %. Continuous infusions of glutamine, arginine (both 50 mg/100 g b.wt. per hour), or alanine (90 mg/ 100 g b.wt. per hour) were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment was followed by a stimulation of renal amino acid reabsorption. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pre-treatment (0.96+/-0.10 vs. 0.62+/-0.07 ml/min x 100 g b.wt.), with a distinct increase in sodium excretion (2.98+/-0.55 vs. 4.97+/-0.71 microval/100 g b.wt. x 20 min) and with a retarded normal kidney weight gain (874+/-18 vs. 775+/-32 mg/100 g b.wt.). A simultaneous PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions.     

Leucine and protein metabolism in rats with chronic renal insufficiency

The aim of this study was to evaluate the effect of chronic uremia induced by 5/6 nephrectomy (5/6NX) on changes in protein and branched-chain amino acid (BCAA; valine, leucine and isoleucine) metabolism. The control group consisted of sham operated rats. Twenty eight weeks after surgery the parameters of protein and amino acid metabolism were evaluated using a primed constant intravenous infusion of L-[1-(14)C]leucine. A drop in BCAA levels and a significant increase in urea, creatinine and cholesterol were observed in plasma of all 5/6NX rats. However, severe uremia with acidosis developed only in one third of rats with 5/6NX. In 5/6NX rats with acidosis significant increases in proteolysis, leucine oxidation, leucine oxidized fraction, and leucine clearance were observed in comparison with the control group and rats with 5/6NX without acidosis. In addition, in 5/6NX rats with acidosis a significant decrease in valine concentration in gastrocnemius muscle was found. We conclude that marked activation of proteolysis occurs in severe chronic renal failure and is probably caused by metabolic changes related to acidosis development.