Loss of the glomerular contractile response to angiotensin in rats following myohemoglobinuric acute renal failure

Tempol Protects Against Acute Renal Injury by Regulating PI3K/Akt/mTOR and GSK3β Signaling Cascades and Afferent Arteriolar Activity

BACKGROUND/AIMS

Free radical scavenger tempol is a protective antioxidant against ischemic injury. Tubular epithelial apoptosis is one of the main changes in the renal ischemia/reperfusion (I/R) injury. Meanwhile some proteins related with apoptosis and inflammation are also involved in renal I/R injury. We tested the hypothesis that tempol protects against renal I/R injury by activating protein kinase B/mammalian target of rapamycin (PKB, Akt/mTOR) and glycogen synthase kinase 3β (GSK3β) pathways as well as the coordinating apoptosis and inflammation related proteins.

METHODS

The right renal pedicle of C57Bl/6 mouse was clamped for 30 minutes and the left kidney was removed in the study. The renal injury was assessed with serum parameters by an automatic chemistry analyzer. Renal expressions of Akt/mTOR and GSK3β pathways were measured by western blot in I/R mice treated with saline or tempol (50mg/kg) and compared with sham-operated mice.

RESULTS

The levels of blood urea nitrogen (BUN), creatinine and superoxide anion (O2.-) increased, and superoxide dismutase (SOD) and catalase (CAT) decreased significantly after renal I/R injury. However, tempol treatment prevented the changes. Besides, I/R injury reduced renal expression of p-Akt, p-GSK3β, p-mTOR, Bcl2 and increased NF-κB, p-JNK and p53 in kidney, tempol significantly normalized these changes. In addition, renal I/R injury reduced the response of afferent arteriole to Angiotensin II (Ang II), while tempol treatment improved the activity of afferent arteriole.

CONCLUSION

Tempol attenuates renal I/R injury. The protective mechanisms seem to relate with activation of PI3K/Akt/mTOR and GSK3β pathways, inhibition of cellular damage markers and inflammation factors, as well as improvement of afferent arteriolar activity.

Increased hydrogen peroxide impairs angiotensin II contractions of afferent arterioles in mice after renal ischaemia-reperfusion injury

AIM

Renal ischaemia-reperfusion injury (IRI) increases angiotensin II (Ang II) and reactive oxygen species (ROS) that are potent modulators of vascular function. However, the roles of individual ROS and their interaction with Ang II are not clear. Here we tested the hypothesis that IRI modulates renal afferent arteriolar responses to Ang II via increasing superoxide (O2-) or hydrogen peroxide (H2 O2 ).

METHODS

Renal afferent arterioles were isolated and perfused from C57BL/6 mice 24 h after IRI or sham surgery. Responses to Ang II or noradrenaline were assessed by measuring arteriolar diameter. Production of H2 O2 and O2- was assessed in afferent arterioles and renal cortex. Activity of SOD and catalase, and mRNA expressions of Ang II receptors were assessed in pre-glomerular arterioles and renal cortex.

RESULTS

Afferent arterioles from mice after IRI had a reduced maximal contraction to Ang II (-27±2 vs. -42±1%, P < 0.001), but retained a normal contraction to noradrenaline. Arterioles after IRI had a 38% increase in H2 O2 (P < 0.001) and a 45% decrease in catalase activity (P < 0.01). Contractions were reduced in normal arterioles after incubation with H2 O2 (-22±2 vs. -42±1%, P < 0.05) similar to the effects of IRI. However, the impaired contractions were normalized by incubation with PEG catalase despite a reduced AT1 R expression.

CONCLUSIONS

Renal IRI in mice selectively impairs afferent arteriolar responses to Ang II because of H2 O2 accumulation that is caused by a reduced catalase activity. This could serve to buffer the effect of Ang II after IRI and may be a protective mechanism.

Evolution of total antioxidant status in a model of acute renal insufficiency in rats

BACKGROUND

Accurate estimation of the Total Antioxidant Status (TAS) in the myoglobinuric acute renal failure (ARF) is necessary because its pathogenesis is believed to be mediated, at least in part, by the development of oxidative stress resulting from the generation of oxygen free radicals and reduced antioxidant defense system. The purpose of this study is to examine the TAS 24 and 72 h after glycerol injection in a model of myoglobinuric-ARF.

EXPERIMENTAL DESIGN

The study was conduced in 28 Sprague-Dawley rats. In group 1 (n = 7) rats were placed into individual metabolic cages and deprived of water during 24 h. afterwards an intramuscular injection of glycerol was administrated (50% vol/vol in sterile saline) 10 mg/100 g of body weight and 24 h later blood samples were collected for biochemical measurements (urea, creatinine, creatine-kinase, and TAS levels). In group 2 (n = 7), rats followed the same conditions than group 1 ones but blood samples were collected 72 h after glycerol injection. In groups 3 (n = 7) and 4 (n = 7) rats didn't receive glycerol injection, and blood samples were collected within 24 and 72 h respectively after they were placed into metabolic cages.

RESULTS

In groups 1 and 2 we observed a renal function decrease, with higher serum levels of urea and creatinine in group 2 (urea levels: 269 +/- 16 mg/dL vs. 586 +/- 147 mg/dL; p < 0.001. Creatinine levels: 2.8 +/- 0.2 mg/dL vs. 5.8 +/- 0.7 mg/dL; p < 0.001). TAS levels in groups 2, 3, and 4 were similar, but in group 1 was significantly lower (group 1: 0.81 +/- 0.2 mmol/L; group 2: 1.3 +/- 0.1 mmol/L; group 3: 1.2 +/- 0.3 mmol/L, and group 4: 1.2 +/- 0.2 mmol/L; p < 0.005).

CONCLUSION

In the model of glycerol induced myoglobinuric-ARF we observed a decrease of serum TAS level within 24 h with spontaneous recuperation 72 h after.

Vascular responses to endothelin-1, angiotensin-II, and U46619 in glycerol-induced acute renal failure

Angiotensin II and endothelin-1, major endogenous vasoconstrictors in acute renal failure (ARF), can modulate the effects of each other. This study aimed to evaluate the interaction between these vasoconstrictors in glycerol-induced ARF by evaluating their effects in the isolated perfused kidney in the presence of their respective antagonists. In ARF, angiotensin II (2.5-25 ng) caused an increase in perfusion pressure. Saralasin, 1 microM, a nonselective angiotensin receptor antagonist, reduced these responses by 61+/- 6% (p < 0.05). Surprisingly, SQ29548, 1 microM, a selective PGH2 /thromboxane A2 receptor blocker, also reduced angiotensin II responses (62 +/- 4%; p < 0.05). BQ610 1 microM, an ETA -selective receptor antagonist, was without effect, but BQ788 1 microM, an ETB -selective antagonist, attenuated the response by 70 +/- 4% (p < 0.05). In ARF, in contrast to angiotensin II, vasoconstriction by endothelin-1 (5-25 ng) was diminished. Saralasin further attenuated endothelin-1 response by 65 +/- 2% (p < 0.05), whereas SQ29548 was without effect. BQ788 reduced the responses by 67 +/- 7% (p < 0.05), whereas BQ610 was without effect (42 +/- 30%; p > 0.05). BQ610 and BQ788 combination further reduced vasoconstriction by 89 +/- 3% (p < 0.05). Responses to U46619 were not changed in ARF. However, saralasin and BQ788, but not BQ610, attenuated its vasoconstrictor action. We conclude that vascular responses in ARF may be attributed to enhanced responses to angiotensin II through activation of ETB and/or PGH2 /thromboxane A2 receptors. We also suggest that the vasoconstrictor response to endothelin-1 in ARF is predominantly ETB receptor-mediated.

Glycerol-induced acute renal failure attenuates subsequent HgCl2-associated nephrotoxicity: correlation of renal function and morphology

Glycerol induced acute renal failure (ARF) is known to attenuate subsequent mercuric chloride nephrotoxicity. This protection was evaluated in rats. Glycerol induced varying degrees of renal insufficiency. After 14 days, when serum creatinine (SCr) creatinine clearance (CCr) and fractional excretion of sodium (FENa) had returned to baseline, injection of mercuric chloride caused significantly milder renal insufficiency in recovered rats than in controls (SCr 356 +/- 46 vs. 475 +/- 19 mumol/L; CCr 0.12 +/- 0.02 vs. 0.02 +/- 0.02 mL/min, p < .05; and mortality 0 vs. 45%, respectively, p < .01). A striking finding was that the degree of renal insufficiency induced by mercuric chloride correlated inversely with the degree of renal insufficiency previously induced by glycerol (r = -0.496, p < .05 for SCr and CCr), but there was no correlation with other measures of previous renal function such as urine volume, sodium excretion, or FENa. Glycerol induced ARF also attenuated the renal toxicity of mercuric chloride injected 4 days after glycerol, before full recovery of renal function. The decrements in renal function after the two insults were also inversely related (r = -0.76, p < .01). A third renal insult with a second mercuric chloride injection after three weeks was still attenuated. However, after the third insult, there was no longer an inverse or any statistical relationship with previous measurements of renal function. Histopathology revealed a good correlation between peak Scr after glycerol, and percentage of tubules undergoing re-generation 14 days later (r = 0.97, p < .01). There was an inverse correlation between Scr after mercuric chloride (administered 14 days after glycerol) and percentage of tubular regeneration seen two days later (r = -0.79, p < .05). The correlations of SCr and CCr with regeneration was greater than the correlations with tubular necrosis, suggesting that the regenerative process is involved in the protection from repeated renal insults. In conclusion, glycerol-induced ARF attenuates subsequent mercuric chloride renal insult. The attenuation correlates directly with the initial glycerol-induced damage, so that the more severe the initial renal insufficiency, the milder the renal insufficiency following subsequent mercuric chloride. This protection can be seen as early as 4 days and also 14 days after previous renal insult. The degree of renal tubular regeneration correlates well with the protection seen, and probably plays a role in acquired renal resistance to repeated insults.

Factors affecting severity of renal injury and recovery of function in acute renal failure

Severity of renal injury and recovery of function in acute renal failure (ARF) are strongly related not only to the magnitude and nature of ARF insult but also to numerous factors in the host which govern renal susceptibility to the insult and repair of renal lesion. Prior ARF affords resistance to a rechallenge with the same or different ARF insult. The mechanisms for this acquired resistance to ARF have not been well established, but suggested mechanisms include (a) increased resistance of regenerated tubular epithelial cells to a rechallenge, (b) glomerular refractoriness to vasoactive substances, (c) failure of damaged kidney to concentrate the toxic substance, (d) enhanced antioxidant enzyme activity in glomeruli, and (e) increased Na(+)-K(+)-ATPase activity in regenerated tubular epithelial cells. Controversy still exists regarding roles of these factors in the resistance to renal failure. Functional and morphologic recovery of postischemic kidney is enhanced by antecedent unilateral nephrectomy but delayed in the presence of the contralateral kidney. The mechanisms for the effect of uninephrectomy remain unsettled. Recent studies suggest contributions of changes in preglomerular vascular resistance; alterations in the environment which follow ischemia to all functioning excretory renal tissues; and altered production and release of vasoactive substances such as angiotensin, endothelin, thromboxane, and atrial natriuretic peptide.

Increased angiotensin II receptor binding with age in isolated rat glomeruli

The current investigation was performed to determine whether there are changes in the renin-angiotensin system with increasing age in rats. Experiments were performed on male Sprague-Dawley rats (50 to 165 days old). There were no changes in plasma renin activity or angiotensin II concentrations, but the number of angiotensin II binding sites in isolated glomeruli increased with increasing age (r = 0.87, P less than 0.01). Since rat weight varies directly with age, we studied the possibility that the increase in receptor number was due to changes in glomerular morphometrics. In a separate group of experiments the diameter of isolated glomeruli was measured, and assuming spherical shape, glomerular volume and surface area were calculated. Glomerular diameter increased with age and weight of the rats (r = 0.99, P less than 0.001). There was a strong linear correlation between the changes in angiotensin II receptor number and glomerular surface area (r = 0.99, P less than 0.001). The number of receptors per unit surface area was independent of rat weight or age (1224 receptors/micron 2). To test the hypothesis that the apparent increase in glomerular angiotensin II receptor sites with increasing age was due to the shape of the glomerulus, additional binding studies were performed on membranes prepared from isolated glomeruli. There were no differences in the number of angiotensin II receptors in membranes from 63 and 112 day-old rats (888 +/- 115 vs. 925 +/- 128 fmol/mg). In additional experiments the effects of increasing age on angiotensin modulation of renal function were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of glomerular responses to vasoconstrictor agents in rabbits recovering from ARF

Glomerular responses to angiotensin II (AII), arginine vasopressin (AVP), and norepinephrine (NE) were estimated in rabbits recovering from uranium-mediated nephropathy or ischemic acute renal failure (ARF) to examine roles of intraglomerular events in resistance to ARF. Uranyl acetate (UA, 0.8 mg/kg) produced ARF in some animals but did not in others. Rabbits recovering from UA-induced ARF were highly resistant to a rechallenge with a larger dose of the agent (2 mg/kg). Their glomeruli did not respond to AII, AVP and NE in vitro. In animals having not experienced ARF following the initial insult, however, resistance to the rechallenge was lower than in animals recovering from ARF, and the glomerular response to contractile stimuli was well sustained. A two hour clamping of the renal artery induced ARF in uninephrectomized rabbits. These animals were not resistant to an additional ischemia in the recovery phase, despite inhibited glomerular contractile responses to AII. These data indicate a nonspecific inhibition of glomerular responses to contractile stimuli in the recovery phase of ARF. It is unlikely, however, that resistance to ARF can be attributed to the loss of the glomerular contractile response.

Glomerular prostaglandins, angiotensin II, and nonsteroidal anti-inflammatory drugs

The glomerulus can, in part, regulate its own flow and filtration characteristics, both of which are determinants of the glomerular filtration rate. This occurs in part as the result of interactions between vasoconstrictors, e.g., angiotensin II (AII), and the vasodilatory prostaglandins E2 or I2. It is well accepted that these prostaglandins modulate the constrictor effects of AII on systemic and renal vasculature. Experimental data accumulated from micropuncture studies, analyses of isolated glomeruli in vitro, and glomerular mesangial cell cultures also support the hypothesis that AII-stimulated production of vasodilatory prostaglandins attenuates AII-induced constriction at the glomerular level as well. These studies help to explain the deleterious actions of nonsteroidal anti-inflammatory drugs on glomerular filtration in clinical conditions associated with a decreased effective blood volume and, therefore, activation of AII and other neurohormonal constrictors. These results have also furthered our understanding of the role of prostaglandins in maintaining renal function in human and experimental renal diseases that may be associated with enhanced hormonal constrictor activity.

Histamine modulates contraction and cyclic nucleotides in cultured rat mesangial cells. Differential effects mediated by histamine H1 and H2 receptors

Histamine influences the glomerular microcirculation and modulates immune-inflammatory responses. In the rat kidney, histamine is synthesized by glomeruli and stimulates cyclic nucleotide production specifically in glomeruli. We investigated the in vitro effect of histamine on cyclic nucleotide accumulation in rat cultured glomerular mesangial and epithelial cells. Histamine stimulated cyclic AMP (cAMP) accumulation in cultured mesangial cells (64.0 +/- 22.1 to 511.4 +/- 86.6 pmol/mg protein, n = 9) but had no effect on cAMP accumulation in epithelial cells. This effect was dose-dependent and time-dependent. Stimulation of cAMP accumulation occurred in the range of 5 X 10(-6) M-10(-4) M histamine with a half maximal stimulatory effect of 2 X 10(-5) M. Initial stimulation was noted by 30 s, and maximum stimulation was observed at 5 min. The H2 antagonist cimetidine (10(-4) M) abolished the stimulatory effect of histamine (10(-4) M), while equimolar concentrations of the H1 antagonist diphenhydramine had no significant effect on cAMP accumulation. Moreover, the specific H2 agonist dimaprit, but not the H1 agonist 2-pyridylethylamine, stimulated cAMP accumulation. Histamine had no effect on cAMP accumulation in epithelial cells or on cyclic guanosine monophosphate accumulation in epithelial or mesangial cells. Since the in vivo infusion of histamine reduces ultrafiltration coefficient and since mesangial cell contraction is thought to be responsible for the reduction in the ultrafiltration coefficient, we examined the effect of histamine on the contractile property of mesangial cells. Histamine (5 X 10(-6)-10(-4) M) contracted mesangial cells, and the H1 antagonist diphenhydramine (10(-4) M) but not the H2 antagonist cimetidine (10(-4) M) prevented histamine (10(-4) M) induced contraction. In addition, the H1 agonist 2-pyridylethylamine, but not the H2 agonist dimaprit, contracted mesangial cells. Histamine and its specific agonists and antagonists induced contraction of isolated glomeruli as assessed by glomerular planar surface area in a manner parallel to their effect on mesangial cells. Cinnarizine (10(-5) M), a Ca++ channel blocker, or Ca++, Mg++-free medium prevented histamine (10(-4) M) induced mesangial cell and glomerular contraction. Thus, histamine enhances cAMP accumulation specifically in mesangial cells via an H2 receptor. In contrast, histamine contracts mesangial cells and glomeruli via an H1 receptor, an effect that is dependent on extracellular Ca++ entry. These findings show that histamine potentially influences intraglomerular hemodynamics via effects on mesangial cell contraction. Moreover, our findings considered with the in vivo observation that histamine reduces kf via and H1 receptor provide further support of the hypothesis that mesangial cell contraction regulates the glomerular capillary surface area available for filtration. Our studies also show that this contractile effect of histamine is dependent on extracellular calcium. The presence of a cAMP system sensitive to histamine may have major implications in the pathogenesis of inflammatory glomerulopathies. Mesangial cells possess characteristics similar to circulating and tissue immune effector cells, including lysosomal enzyme release, oxygen radical production, and release of a number of immunomodulatory factors. Histamine and cAMP have been shown to modulate such characteristics of inflammatory cells. It is therefore conceivable that histamine, via its interaction with H2 receptors and subsequent generation cAMP, may have profound effects on such properties of mesangial cells, suggesting that this autacoid may modulate not only glomerular hemodynamics but also immune, inflammatory responses within the glomerulus.

Mechanism of sodium modulation of glomerular angiotensin receptors in the rat

Specific binding of 125I-angiotensin to high affinity glomerular receptors varies directly with the level of dietary sodium. To investigate the mechanism of sodium regulation of glomerular angiotensin receptors, groups of Sprague-Dawley rats were maintained on one of three levels of sodium intake for at least 5 d: high sodium (7.39 meq/24 h), moderate sodium (0.88 meq/24 h), and low sodium diets (0.01 meq/24 h). An additional group was given low sodium diet with daily injections of furosemide (1 mg/kg i.p.). To dissociate the effects of dietary sodium from those of circulating angiotensin II levels on glomerular receptor regulation, a fifth group was placed on high sodium diet and given a continuous infusion of angiotensin via an implanted minipump (100 ng/min) for 21 d. There was a strong negative correlation (r = -0.98, P less than 0.01) between plasma angiotensin II and glomerular angiotensin receptor density. Dietary sodium, potassium, or water consumption did not correlate with angiotensin II receptor concentration. The affinity constant did not vary in any of the groups (2.33 +/- 0.30 X 10(8) M-1). The time course of sodium regulation of glomerular angiotensin II receptors was studied in rats switched from a moderate sodium to either a high sodium diet or a low sodium diet plus furosemide. Receptor density was unchanged at 24 h, varied directly with sodium intake for 1-5 d when induction was maximal, and remained constant for at least 21 d. The time course of receptor regulation closely paralleled changes in plasma angiotensin II. Additional studies were undertaken to demonstrate that glomerular angiotensin II receptors are down-regulated by circulating hormone. Rats maintained on moderate sodium intake were killed 2 min after the induction of anesthesia with pentobarbital (50 mg/kg i.p.) or by rapid decapitation. Despite a 50-fold elevation of plasma angiotensin II in anesthetized rats (424 +/- 154 vs. 8.6 +/- 1.0 pg/ml, P less than 0.001) angiotensin receptor density was unchanged (anesthetized, 1,016 +/- 126 vs. unanesthetized, 1,290 +/- 84 fmol/mg). The infusion of angiotensin II (100 mg/min) for 15 min or 2 h into anesthetized rats maintained on moderate sodium intake resulted in a 50% reduction in specific angiotensin binding that could not be reversed by the dissociation of endogenous angiotensin. These data are compatible with modulation of receptor density by circulating hormone and can not be accounted for by prior receptor occupancy.