Experimental nephrology最新文献

Bilateral clamping of renal pedicles during 60, 75 or 90 min was used to characterize the evolution of ischemic acute renal failure (ARF) in prepubertal rats. To verify the existence of age-conditioned differences in the evolution of ARF, adult rats were exposed to 40, 60 or 75 min of clamping. After 7 days, survival rate was significantly better in young than adult rats for identical times of clamping (89 vs. 35% for 60 min and 69 vs. 35% for 75 min). Young rats largely died within the first 24 h following ischemia while the risk of death extended until the 4th day after ischemia in adult rats. Peak values of serum urea nitrogen and creatinine were observed on the 1st and 3rd day after ischemia in young and adult rats, respectively. In young rats, these markers of renal function returned to normal on days 5 and 6 whereas they remained elevated at the end of the study in adult animals. Growth curves of young rats paralleled those of sham-operated animals from the 3rd day of clamping whereas adult rats did not even reach the initial weight at the end of the study. Analysis of kidneys obtained 7 days after clamping revealed more severe histopathological lesions in adult rats as well as a higher proliferative activity (10-40 times the value of sham-operated animals versus 2-4 times the control value in young rats). Our findings indicate that kidneys from young rats are more resistant to ischemia and recover more quickly from the ischemic insult. Therefore, the experimental model of ischemic ARF is clearly different in young and adult rats.

The elucidation of the pathogenesis of human renal disease at the molecular level has been facilitated by the growing field of gene targeting and the development of mouse strains with single-gene deletions - the 'knock-out' mice. Experimental nephrology, therefore, requires well-characterized and reliable models of human renal disease that can be induced reproducibly in mice. Today surgical procedures for the induction of renal ischemia, chronic renal failure, and ureter obstruction are feasible in mice. Models of mesangioproliferative or crescentic glomerulonephritis, glomerulosclerosis, and tubulointerstitial disease are readily available; however, these depend heavily on the mouse genetic background. Attention to the genetic background and appropriate backcrossing are, therefore, of great importance in the design and interpretation of experimental studies, especially in transgenic mice. Simple murine models displaying the clinical features of other human renal diseases such as IgA nephropathy, membranous glomerulonephritis, and renal vasculitis are still lacking. Mouse strains that spontaneously develop distinct renal pathologies similar to lupus nephritis and focal-segmental glomerulosclerosis can be intercrossed with transgenic mice to study the impact of single-gene deletions on the renal phenotype. The present review provides a survey about currently available spontaneous and inducible murine models of renal disease with special attention to problems and future perspectives for their use in transgenic animals.

Background/aims: Leukotriene A(4) (LTA(4)) hydrolase catalyzes the final step in the synthesis of leukotriene B(4) (LTB(4)). TH-1- and TH-2-derived cytokines may regulate LTB(4) synthesis by monocytes through their actions on the expression of LTA(4) hydrolase.

Methods: Freshly isolated monocytes were incubated with pro- and anti-inflammatory cytokines for 36 h. mRNA expression was determined by Northern blot, protein expression was determined by Western blot and LTB(4) synthesis was determined by ELISA.

Results: Interferon-gamma (a TH-2-derived cytokine) increased significantly LTA(4) hydrolase mRNA expression, whereas interleukin (IL)-4 and IL-13 (both TH-2-derived cytokines) decreased LTA(4) hydrolase mRNA expression in these cells. The same effects were seen on the expression of immunoreactive LTA(4) hydrolase after incubating the monocytes with either TH-1- or TH-2-derived cytokines. The monocyte-derived cytokine IL-1 beta did not show any significant effect on LTA(4) hydrolase mRNA expression. When LTB(4) release was measured, both IL-1 beta and interferon-gamma significantly increased LTB(4) production by monocytes, while TH-2 cytokines (IL-4 and IL-13) decreased it.

Conclusion: The opposing effects of TH-1- and TH-2-derived cytokines on the expression of LTA(4) hydrolase mRNA may regulate LTB(4) synthesis by monocytes during inflammation.

The cDNA for the seventh mammalian aquaporin (AQP7) was isolated from rat testis, and its expression was demonstrated at the tail of late spermatids [Ishibashi et al: J Biol Chem 1997;272:20782-20786]. AQP7 is also expressed in the kidney. The localization of AQP7 in the kidney is unknown. We examined the cellular localization of AQP7 in the kidney with Northern blot, reverse transcribed PCR, Western blot and immunohistochemistry in the rat kidney. In Northern blot, AQP7 was expressed in the cortex and the outer medulla but absent in the inner medulla of the kidney. Reverse transcribed PCR of rat nephron segments revealed the selective expression of AQP7 at the proximal straight tubules (PST). Western blot of the membrane fraction of outer medulla revealed a single band of approximately 33 kDa. Immunohistochemistry of the rat kidney showed the selective expression of AQP7 at the brush border membranes of PST (S3 segment). AQP7 is now shown to be localized selectively at the brush border membranes of PST in the rat kidney. The result suggests that AQP7 may function as a pathway for transcellular water transport in PST in concert with more widely expressed AQP1 in proximal tubules. Alternatively, as AQP7 transports urea as well as water, AQP7 may function as a passive urea secretory pathway in this segment and may play a role in the formation and/or maintenance of the medullary urea concentration gradient.

The pathogenesis of sepsis-induced renal failure is multifactorial and only partially understood. In these studies we evaluated intrarenal microcirculatory changes during endotoxemia and the potential role of nitric oxide (NO) and endothelin in these changes. In anesthetized rats endotoxin infusion [lipopolysaccharide (LPS), Escherichia coli serotype 0127:B8; 10 mg/kg/h] resulted in hypotension and a transient enhancement of renal blood flow, with cortical vasodilation and a loss of outer medullary vasodilatory response to hypotension. The initial cortical vasodilation was abolished by the NO synthase inhibitor NG-nitro-L-arginine methyl ester, but not by indomethacin. Direct NO measurements disclosed a gradual rise in cortical NO, despite the waning vasodilatory effect, suggesting antagonizing vasoconstrictive stimuli. In rats pretreated by LPS (1 mg/kg i.p. 1 day earlier) the renal blood flow was reduced to 55% of that of controls. Moreover, the vasodilatory response to LPS infusion was converted into profound cortical and medullary vasoconstriction. In these preconditioned rats the endothelin receptor antagonist bosentan evoked a vasodilatory response and attenuated the vasoconstrictive reaction to LPS infusion. The infusion of another LPS (E. coli serotype 0111:B4) exerted predominant and protracted renal vasodilation without hypotension. In conclusion, different LPS exert diverse systemic and renal hemodynamic responses. The 0127:B8 serotype attenuates renal medullary vasodilation during hypotension, exerts transient cortical vasodilation, and following repeated exposure induces profound renal vasoconstriction. NO and endothelin participate in LPS-induced vascular responses that may predispose to hypoxic tubular damage.

Endotoxin-induced hypotension and altered renal microcirculation could lead to tubular injury, particularly at the physiologically hypoxic outer medulla. We explored this hypothesis in isolated perfused kidneys and in vivo in rats subjected to endotoxemia. Rat kidneys were removed 15 min after endotoxin injection in vivo (from Escherichia coli 0127:B8, 1 mg/kg i.p.) and perfused with oxygenated medium supplemented with 20 amino acids and endotoxin. Glomerular filtration rate and filtration fraction markedly declined (0.4 +/- 0. 1 ml/min and 1.1 +/- 0.1, respectively) as compared with control kidneys (0.7 +/- 0.1 ml/min and 1.8 +/- 0.1, n = 8-12 per group; p < 0.05). Hypoxic injury to medullary thick ascending limbs in the innermost outer medulla increased (47 +/- 9% of tubules vs. 16 +/- 8% in controls, p < 0.05). When rats were preconditioned with an additional endotoxin injection 16 h earlier (a manipulation that markedly reduces cortical and medullary blood flow), glomerular filtration rate and filtration fraction further declined to 0.1 +/- 0.0 ml/min and 0.4 +/- 0.1, respectively (p < 0.01), and tubular sodium reabsorption fell to 81 +/- 12 vs 98 +/- 0% in controls (p < 0.05). Tubular damage, however, did not increase (20 +/- 7%), probably reflecting a decline in reabsorptive workload and oxygen requirement. In rats subjected to a single or two repeated daily doses of endotoxin (1 mg/kg i.p.) plasma creatinine comparably rose 41% on the average over 24 h, creatinine clearance fell by 27% (p < 0.0001), but tubular damage was absent. By contrast, in rats preconditioned with indomethacin and the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (10 mg/kg), the addition of endotoxin markedly augmented outer medullary hypoxic tubular damage both in S(3) segments (27 +/- 10 vs 1 +/- 1%) and in medullary thick ascending limbs (38 +/- 11 vs. 10 +/- 5%, n = 7-8; p < 0.05). It is concluded that under special conditions, such as altered medullary oxygen balance or defective nitric oxide or prostaglandin synthesis, endotoxin may predispose to hypoxic outer medullary tubular damage.

The balance of the vascular tone between afferent and efferent arterioles (AAs and EAs, respectively) is a crucial determinant of glomerular hemodynamics. Thus, it is important to study the mechanisms that control their vascular tone to understand renal physiology and pathophysiology. In order to directly study the mechanisms that regulate their vascular tone, we have developed several in vitro microperfusion preparations of these arterioles, which have the advantage of allowing us to observe the arteriolar diameter directly in the absence of systemic hemodynamic and hormonal influences. In the AA but not EA, we have directly demonstrated the presence of two intrinsic mechanisms, namely the myogenic response and macula densa-mediated tubuloglomerular feedback, that play an important role in the control of vascular tone. We also found that both mechanism-induced constrictions of AAs can be modulated by endogenous nitric oxide. In addition, several humoral factors (such as angiotensin II or prostaglandins) play an important role in the control of AA tone. On the other hand, angiotensin II is one major factor that controls the vascular tone of the EA. We have found that the vasoconstrictor effect of angiotensin II on EAs is modulated by prostaglandins produced by the upstream glomerulus. Thus, this may be a mechanism whereby the glomerulus controls its own capillary pressure by releasing prostaglandins and thereby adjusting the resistance of the downstream EA. These varying mechanisms regulating AA and EA tone play an important role in the precise control of glomerular hemodynamics.

Background: Delayed renal function after transplantation is a strong predictor of long-term graft survival. As an increased expression of endothelin (ET) has been demonstrated during ischemia/reperfusion injury, we hypothesized that ET-A receptor blockade could improve the recovery of acute renal failure in a rat model of isogeneic kidney transplantation.

Methods: Kidneys of Fisher (F344, RT1(1v1)) rat donors flushed with cooled University of Wisconsin solution were transplanted into bilaterally nephrectomized Fisher rats. Recipient animals were treated orally either with vehicle or the selective ET-A receptor antagonist LU135252 (30 mg/kg/day p.o.) for 14 days. Unilaterally nephrectomized Fisher rats not subjected to ischemia served as controls. No immunosuppression was given. On days 2, 6 and 14, metabolic studies were performed to evaluate endogenous creatinine clearance, fractional sodium excretion, and urinary endothelin excretion. Kidneys were harvested at the end of the experiment for determination of renal ET content and immunohistochemical assessment.

Results: Urinary ET excretion was increased in vehicle-treated isografts compared to uninephrectomized controls after 14 days. Treatment with LU135252 resulted in a significant improvement in creatinine clearance and fractional sodium excretion to the level of uninephrectomized rats after 14 days. Isografts treated with selective ET-A receptor blockade demonstrated a marked reduction in cell surface markers for macrophages/monocytes, T cells, MHC-II, and ICAM-1.

Conclusion: Treatment with the selective ET-A receptor antagonist LU135252 accelerates recovery of renal function after isogeneic renal transplantation and attenuates cellular graft infiltration. This effect could have major implications for the treatment of patients undergoing renal transplantation, as an improved initial renal function may delay the onset of chronic allograft rejection.

Application of the TUNEL method and immunostaining cell-specific markers to a whole isolated glomerulus in combination with confocal laser scan microscopy can be used to analyze cell turnover including apoptosis within glomeruli. Furthermore, the technologies can be used to deepen our understanding of glomerular cell biology and pathophysiology at the cellular and molecular levels.

Nonsteroidal anti-inflammatory drugs can impair renal perfusion through inhibition of cyclooxygenase (COX)-mediated prostaglandin synthesis. We investigated the influence of the preferential COX-2 inhibitor, meloxicam (MELO), on renal hemodynamics in eu- and hypovolemic rats compared to the nonselective COX inhibitor indomethacin (INDO). The hypovolemic state was obtained in rats by three daily injections of furosemide (2 mg/kg i.p.) followed by a sodium-deficient diet for 7 days. In euvolemic rats (n = 6) neither INDO (5 mg/kg i.v.) nor MELO (1 or 2 mg/kg i.v.) influenced mean arterial blood pressure (MAP) or impaired renal (RBF) and cortical blood flow (CBF). Medullary blood flow (MBF) decreased after INDO (18%; p<0.05), and dose-dependently after MELO (1 mg, 10%; 2 mg, 18%; p<0.05). In hypovolemic rats (n = 6) INDO and MELO had no effect on MAP. RBF and CBF were reduced after INDO (11 or 20%; p<0. 05), but showed no changes after MELO. INDO induced a decrease in MBF (22%; p<0.05) which was less pronounced after MELO (12%; p <0.05). In conclusion the preferential COX-2 inhibitor MELO compromized renal perfusion in the outer medulla both in eu- and hypovolemic animals.