Hours Of Unilateral Ureteral Obstruction Research Articles

Validation of quantitative BOLD MRI measurements in kidney: Application to unilateral ureteral obstruction

Blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) provides a measure of deoxyhemoglobin content and therefore an indirect measure of the partial oxygen pressure (pO(2)). The main purpose of this study was to examine the relationship between the apparent relaxation rate (R2*) in the pig kidney by BOLD imaging and renal tissue pO(2) levels measured directly by oxygen-sensitive microelectrodes. Second, BOLD imaging was applied to kidneys in pigs subjected to acute unilateral ureteral obstruction (UUO) to examine whether this condition is associated with changes in intrarenal oxygenation. Oxygen-sensitive microelectrodes were inserted in the cortex and medulla of pig kidneys (N= 6). Different arterial and intrarenal levels of pO(2) were obtained by stepwise changing the oxygen-to-nitrogen ratio supplied by a respirator. Simultaneous BOLD MRI measurements using an R2*-sensitive Echo Planar Imaging (EPI) sequence were performed on the contralateral kidney. In another group of pigs (N= 3) BOLD imaging was performed following 24 hours of UUO. When the inhaled oxygen fraction was 5% to 70%, R2* was linearly related to pO(2) levels (cortex DeltaR2*/DeltapO(2)=-1.2 ms(-1)kPa(-1), and medulla DeltaR2*/DeltapO2 =-1.7 ms(-1)kPa(-1)). Twenty-four hours of UUO was associated with an increased R2* in the cortex and a decreased R2* in medulla as compared with baseline, which remained augmented after the release of UUO, indicating that pO(2) levels were reduced in the cortex and increased in the medulla during and after release of obstruction. BOLD MRI provides noninvasive estimates of regional renal oxygen content and our study demonstrates that this technique may provide a useful tool in UUO which is associated with altered renal oxygen consumption.

Liposome-mediated transfer of nitric oxide synthase gene improves renal function in ureteral obstruction in rats

The protective effect of nitric oxide has been demonstrated in several renal disease models. We augmented renal nitric oxide production by transfer of the inducible nitric oxide synthase (iNOS) gene into rat kidney in controls and in unilateral ureteral obstruction (UUO). The human iNOS gene was inserted into a pcDNA 3.1-backbone plasmid with the FLAG epitope (FLAG-iNOS). In vitro, transduction of FLAG-iNOS was confirmed by Western blot and Griess reaction. In vivo, we transfected either FLAG-iNOS or control plasmid (CMV-LacZ), using cationic liposomes. Urinary nitric oxide metabolites and immunohistochemistry confirmed iNOS transduction. Renal function was also assessed. In vitro, increased iNOS expression was demonstrated in human embryonic kidney (HEK293) cells, along with increased release of nitric oxide metabolites, NO(2)/NO(3). In vivo, FLAG-iNOS was detected by polymerase chain reaction (PCR) up to 35 days after the transfection. Urine collection documented increased urinary NO(2)/NO(3). Immunohistochemistry localized iNOS to collecting ducts, distal tubules, and glomerulus of the injected kidney. Renal function measured up to 21 days after transfection in control animals was not significantly different between the two groups. In contrast, renal function after 24 hours of UUO was significantly improved in FLAG-iNOS-treated animals. This study demonstrates the feasibility of liposome-mediated iNOS gene transfer into the kidney. Furthermore, the improvement of renal function in UUO demonstrates that the transfected iNOS gene is active and suggests that decreased iNOS activity contributes to the decreased renal function in UUO. This iNOS construct may have therapeutic utility in the pathophysiologic sequelae of UUO and other renal diseases.

Dietary L-Arginine Supplementation Improves the Glomerular Filtration Rate and Renal Blood Flow After 24 Hours of Unilateral Ureteral Obstruction in Rats

Unilateral ureteral obstruction (UUO) results in a significant change in renal blood flow (RBF) and glomerular filtration rate (GFR) by 24 hours. The intake of L-arginine, a substrate of nitric oxide (NO) synthase (NOS), can augment NO production. NO can maintain renal function through its vasodilatory action. Therefore, we examined the effect of dietary arginine supplementation on renal function in UUO. GFR and RBF were measured by inulin and para-aminohippurate clearance, respectively, in control rats and in rats 24 hours after UUO. Rats were given arginine with or without the concomitant administration of N-nitro-L-arginine methyl ester. Urinary nitrate/nitrite (NO2/NO3) was measured by the Griess reaction and urinary cyclic guanosine monophosphate was determined by enzyme-linked immunosorbent assay. The expression of renal inducible NOS was determined by immunohistochemistry. Urinary NO2/NO3 was significantly increased after 2 weeks of arginine, confirming increased NO production. In control rats GFR and RBF were not significantly different in untreated vs arginine treated groups. In contrast, arginine treatment significantly increased GFR in the obstructed kidney (0.06 +/- 0.01 to 0.14 +/- 0.02 ml per minute per 100 gm) and the contralateral kidney compared with control UUO. RBF was also significantly increased by arginine. The increases in renal function with arginine were blunted by a NOS inhibitor in obstructed and contralateral kidneys. Inducible NOS expression was increased in obstructed and contralateral kidneys. This study demonstrates that L-arginine supplementation can improve renal function in acute UUO. This finding suggests that NO system may be a future site of pharmacological intervention for UUO.

MRNA expression of chemokines in rat kidneys with ureteral obstruction

It has been demonstrated that leukocyte infiltration, mainly of macrophages and lymphocytes, into obstructed kidneys (OBK) of rats during unilateral ureteral obstruction (UUO). Chemokines (C-C subfamily) may be involved in this mechanisms. Thus, we accessed the gene expression of chemokines in renal cortex of rats with UUO. Female SD rats were sacrificed at various time points after UUO. mRNA expression of MCP-1, RANTES and MIP-1 alpha was determined by semi-quantitative RT-PCR. Control kidneys (CNK) showed a weak mRNA expression of MCP-1, RANTES and MIP-1 alpha. OBKs showed an increase in MCP-1 at 2 hours of UUO and a significant increase at 4 hours of UUO as compared with CNKs or contralateral unobstructed kidneys (CLK). The mRNA levels of RANTES and MIP-1 alpha were not increased until 72 hours of UUO in CLKs or OBKs. There were slight, but significant, differences of RANTES and MIP-1 alpha expression between OBKs and CNKs at 120 hours of UUO. We suggest that the early increase in MCP-1 contributes to the leukocyte infiltration and that RANTES and MIP-1 alpha plays a partial role in a late increases.

RECOVERY OF DISTAL NEPHRON ENZYME ACTIVITY AFTER RELEASE OF UNILATERAL URETERAL OBSTRUCTION

Unilateral ureteral obstruction (UUO) for 24 hours results in a severe compromise of distal tubular function. The acidification defect is believed to be localized in the collecting duct. To characterize distal tubular function recovery one month after junction release, clearance studies in whole animals and enzyme studies in microdissected segments were performed in an experimental model of unilateral ureteral obstruction. Following release of ureteral obstruction of 24 hours duration, a significant decrease of whole kidney glomerular filtration rate was observed in the postobstructed kidney (POK) with a marked increase in urinary pH, fractional excretion of bicarbonate (FEHCO3-) and decrease in urinary osmolality. By orthograde stop flow experiment, bicarbonate excretion rate (Fr:Ff HCO3-/Fr:Ff Inutest) increased in the first and second urine fractions of 120 microl. corresponding to the collecting segment in the POK, one day after release. Decrease in U-P pCO2 (p<0.01) suggested an impaired H+ secretion on distal nephron in POK. Recovery of inulin clearance and values of urinary pH, FEHCO3- and urinary osmolality near contralateral and control kidneys were observed thirty days following ureteral release. The decline in enzyme activity in the distal nephron due to structural damage from high intratubular pressure was evaluated. Bafilomycin sensitive H+ -ATPase activity measurement in the medullary collecting duct segments of the POK showed an important decrease (68%), with lightly reduced activity (20%) in the cortical collecting duct, 24 hours after obstruction release. Localized in the connecting tubule cells and secreted into the tubular fluid in the late distal nephron, renal kallikrein has been involved in bicarbonate transport at cortical collecting duct segments. The renal kallikrein-like activity was reduced in POK (p<0.01). Recovery of enzyme activity was shown thirty days after unilateral ureteral obstruction. Our results show severe functional damage of the collecting duct after 24 hours of unilateral ureteral obstruction. H+ -ATPase activity was markedly decreased on medullary collecting duct segments. A correlation between the functional impairment of distal H+ secretion and decreased distal nephron enzyme activity has been shown. Recovery of both the functional and the enzyme activity at the distal nephron was demonstrated thirty days after obstruction release.

Sequential changes in renal expression of renin-angiotensin system genes in acute unilateral ureteral obstruction

Unilateral ureteral obstruction (UUO) alters the expression of genes encoding for the renin-angiotensin system (RAS). We tested the hypothesis that changes in RAS genes expression occur soon after obstruction. Indeed, measurements during the first 24 hours of UUO showed up-regulation of renin mRNA in the obstructed kidney at 1 hour. UUO also led to increases in PRA and renal renin content, ACE activity and Ang II concentration in the experimental kidney. The obstructed kidney relative abundance of renin mRNA was increased compared to basal at 1, 2, 6, and 24 hours; the contralateral kidney renin mRNA expression was reduced. AT1-R mRNA expression was diminished at 6 and 24 hours in the obstructed kidney compared to contralateral and sham kidneys. ACE activity was up-regulated in the obstructed kidney and transiently down-regulated in the contralateral kidney. These findings show for the first time that activation of the RAS results from as little as 1 hour of UUO and that up-regulation of renin mRNA and ACE activity lead to increase Ang II production which down-regulates AT1-R mRNA as early as 6 hours post-UUO. These studies establish a pattern of sequential, differential regulation of the RAS genes in acute UUO that provide an explanation for the hemodynamic changes in this condition.

Volume Expansion Enhances the Recovery of Renal Function and Prolongs the Diuresis and Natriuresis After Release of Bilateral Ureteral Obstruction: A Possible Role for Atrial Natriuretic Peptide

Plasma atrial natriuretic peptide (ANP) levels are elevated in patients with bilateral ureteral obstruction (BUO). To further evaluate the role of ANP in postobstructive diuresis, natriuresis and recovery of renal function, 3 groups of dogs were studied: Group 1, 6 dogs that underwent 48 hours of unilateral ureteral obstruction (UUO); Group 2, 6 dogs that underwent 48 hours of BUO; and Group 3, 6 dogs volume replete with normal saline during 48 hours of BUO. All 3 groups underwent hourly hemodynamic and clearance studies for 15 hours after the release of obstruction. Group 1 experienced no increase in either urine output or sodium excretion from the ipsilateral or contralateral kidney after release of obstruction. Groups 2 and 3 both experienced an initial diuresis and natriuresis after BUO (p less than 0.01). However, in Group 2 diuresis and natriuresis after BUO ceased at 5 and 2 hours, respectively, while in Group 3 both persisted for 10 and 9 hours, respectively. Before obstruction the GFR was similar in all three groups. In Group 1 the GFR decreased significantly in the ipsilateral kidney (34.5 plus/minus 1.4 to 14.48 plus/minus 1.5 ml. per minute, (p less than 0.01)) and increased significantly in the contralateral kidney (32.4 plus/minus 2.8 to 44.4 plus/minus 2.0 ml. per minute, (p less than 0.05)) and remained so throughout the postobstruction period. The GFR in Groups 2 and 3 decreased to a similar level 1 hour after release (13.3 plus/minus 1.7 and 17.5 plus/minus 3.4 ml. per minute, respectively); however, Group 2 remained decreased during the period after release while group 3 increased to 23.4 plus/minus 3.4 ml. per minute (p less than 0.01) at 11 hours after release of obstruction. In Group 2 the control plasma ANP level was 17.9 plus/minus 3.7 pg./ml. and was not altered by BUO, whereas ANP increased significantly after 48 hour BUO in Group 3, from 30.6 plus/minus 6.7 to 63.7 plus/minus 11.7 pg./ml. (p less than 0.01). Before and after 48 hours of BUO, the pulmonary capillary wedge pressure was 5.0 plus/minus 2.0 mm. Hg and 7.0 plus/minus 1.0 mm. Hg (NS) in Group 2, while it increased from 7.18 plus/minus 1.5 mm. Hg to 11.6 plus/minus 1.9 mm. Hg (p less than 0.01) in Group 3. We conclude that volume expansion during BUO enhances postobstructive diuresis and natriuresis and allows a greater recovery of GFR after release of the obstruction. This effect may be mediated through elevated plasma levels of ANP as measured in this study.

Thromboxane A2 receptor blockade improves renal function and histopathology in the post-obstructive kidney

To elucidate the role of the vasoconstrictor thromboxane A2(TXA2) in post-obstructive nephropathy, we examined the effect of the TXA2 receptor antagonist GR32191(GR) on renal function and histopathology in the post-obstructed kidney (POK) in rats. Rats pre-treated with 3 or 6 mg/kg i.p. of GR prior to ureteral obstruction and maintained on b.i.d. doses of GR were compared to vehicle-treated and sham-operated controls. Renal hemodynamic, clearance and excretory function were assessed in each kidney following relief of 24 hours of unilateral ureteral obstruction. The histology of each kidney was evaluated. Mean clearances of inulin for the POK were significantly greater in the treated rats (0.42 +/- 0.06 ml/min at 6 mg/kg) than in controls (0.13 +/- 0.04 ml/min) and a dose-response effect was observed (P < 0.05). Paraaminohippurate clearance was increased by > 150% and renal vascular resistance was reduced by 50% in GR treated animals compared with controls (P < 0.05). Histopathologic findings in the untreated POK were typical of early obstruction. In the GR treated groups these changes were much less severe. These data support an important role for TXA2 in the pathogenesis of post-obstructive nephropathy.

The impact of total unilateral ureteral obstruction on intrarenal angiotensin II production in the polycalyceal pig kidney.

Nine pigs with unilateral complete ureteral obstruction were investigated for 15 hours. Obstruction of the ureter resulted in a maximum intrapelvic pressure of 60 cmH2O within the first hour after obstruction, and a gradual decline to 40 cmH2O during the next 15 hours. In 6 pigs both renal veins were catheterized together with the abdominal aorta allowing measurement of the hormonal difference over the kidney. Plasma angiotensin II, plasma vasopressin and plasma atrial natriuretic peptide concentrations were determined. Arterial concentration of plasma angiotensin II gradually increased from 38.7 pg/ml to 252.3 pg/ml. The highest concentrations of angiotensin II were found from the ipsilateral renal vein. From 1 hour after obstruction and onward there was a negative extraction ratio of angiotensin II from the ipsilateral kidney indicating enhanced intrarenal generation of angiotensin II. No difference in vasopressin was found among the sample sites, but a significant reduction in vasopressin from 15.2 pg/ml to 4.9 pg/ml was found from the ipsilateral renal vein during the 15 hours of unilateral ureteral obstruction. Arterial atrial natriuretic peptide concentrations were higher than renal venous levels at all times. Glomerular filtration was immediately reduced to 58%. It is suggested that an increased ipsilateral generation of intrarenal angiotensin II is at least partly responsible for some of the changes in kidney function during acute obstruction.

Expression of Renin and Its mRNA in the Adult Rat Kidney With Chronic Ureteral Obstruction

Angiotensin II has been implicated in mediating renal vasoconstriction resulting from chronic unilateral ureteral obstruction (UUO) in both mature and developing animals. We have previously shown that chronic neonatal UUO results in increased distribution of renin and its mRNA in the obstructed kidney, as well as of immunoreactive renin in the intact opposite kidney. The present study was designed to evaluate the effects of 24 hours versus 4 weeks of UUO on the distribution of renin mRNA and its protein in the adult rat kidney. Renin was detected by immunocytochemistry using a polyclonal anti-rat renin antibody. Renin mRNA was localized by in situ hybridization to an oligonucleotide complementary to renin mRNA. UUO of 24 hours' or 4 weeks' duration did not alter the distribution of renin and its mRNA in the obstructed kidneys as compared with sham-operated kidneys, although kidneys obstructed for 4 weeks had a significant increase in the percent of renin-containing juxtaglomerular apparatuses (JCA) when compared with the intact opposite kidneys (P less than 0.05). Compensatory hypertrophy was not present in the intact opposite kidneys after 24 hours of UUO and distribution of renin gene expression was not altered at that time. However, 4 weeks following contralateral UUO, the intact kidneys were hypertrophied and showed a decrease in renin gene expression relative to the obstructed and sham-operated kidneys. We conclude that unlike UUO during early development, chronic UUO in the mature animal does not activate renin gene expression nor alter renin distribution in the obstructed kidneys. Renin gene expression is suppressed in the hypertrophied kidney with prolonged contralateral UUO.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal effects of aprotinin after 24 hours of unilateral ureteral obstruction

We have previously demonstrated that, after the release of 24-h unilateral ureteral obstruction (UUO), glomerular filtration rate (GFR), and renal blood flow (RBF) are reduced because of increased production of the potent vasoconstrictors thromboxane A2 (TxA2) and angiotensin II (ANG II). Captopril, which blocks ANG II production, increases GFR and RBF. Sequential administration of aprotinin, a kallikrein inhibitor, has an additive effect to further decrease renal vasoconstriction, even though kinins are generally thought to be vasodilators. Therefore, we assessed mechanisms by which aprotinin might improve renal function of previously obstructed anesthetized rats. When given alone to UUO rats, aprotinin improved renal hemodynamics. Since kinins stimulate TxA2 production by UUO kidneys perfused in vitro, our data suggest that aprotinin improved postobstructive function by decreasing kinin-stimulated TxA2 production, although this may not be its only effect. Aprotinin also improved postobstructive function, even if TxA2 formation was blocked with indomethacin. But when both ANG II and TxA2 formation were blocked by the simultaneous administration of captopril and indomethacin, aprotinin had no effect. This suggests that aprotinin may also affect ANG II formation. These pharmacological effects of aprotinin suggest that the kallikrein-kinin system may also contribute to postobstructive renal vasoconstriction by stimulating the production of both vasoconstrictor eicosanoids and ANG II.

The effect of 2 hours of complete unilateral ureteral obstruction on tubuloglomerular feedback control.

The mechanisms affecting renal blood flow and filtration during and after unilateral ureteral obstruction (UUO) are incompletely understood. Since ureteral obstruction leads to changes in interstitial pressure and volume, and since we have previously shown that interstitial pressure conditions can modulate the sensitivity of the tubuloglomerular feedback (TGF) control system, we sought in the present study to define the contribution of the TGF system to changes in GFR during and after UUO, and to observe associated changes in pressures in vessels, tubules and the interstitial space. Interstitial pressures and glomerular filtration rate (GFR) were measured in one group of Sprague Dawley rats. Interstitial hydraulic pressure was determined with a thin catheter placed in the subcapsular space. Interstitial oncotic pressure was estimated from the protein concentration in collected hilar lymph. In a second group of rats proximal tubule pressure (PT) and stop-flow pressure (PSF) were measured during the first three hours of UUO and after 24 h UUO. In a third group of rats PSF was measured while the loop of Henle was perfused at different rates. The sensitivity of the TGF system was determined from the maximal drop in stop-flow pressure (delta PSF) and the turning point (TP)--the tubule perfusion rate at which 50% of this maximal stop-flow pressure response was obtained. In a fourth group of rats proximal tubule flow-rate was measured after release of 2 hrs UUO. The results show that PT and PSF are both increased during the first three hours of obstruction and that they return to normal or sub-normal levels after 24 h of UUO.(ABSTRACT TRUNCATED AT 250 WORDS)