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J Frøkiaer

Publications and source records attributed to J Frøkiaer.

At least 19 recordsLinked to original sources
PubMed2007

Regulation and dysregulation of aquaporins in water balance disorders.

The discovery of aquaporin-1 (AQP1) explained the long-standing biophysical question of how water specifically crosses biological membranes. These studies led to the identification of a whole new family of membrane proteins, the aquaporin water channels. At present, at least eight aquaporins are expressed at distinct sites in the kidney and four members of this family (AQP1-4) have been demonstrated to play pivotal roles in the physiology and pathophysiology for renal regulation of body water balance. In the present review, a number of inherited and acquired conditions characterized by urinary concentration defects as well as common diseases associated with severe water retention are discussed with relation to the role of aquaporins in regulation and dysregulation of renal water transport.

Animals↗
PubMed2006

Dysregulation of renal sodium transporters in gentamicin-treated rats.

We aimed to investigate the molecular mechanisms underlying the renal wasting of Na(+), K(+), Ca(2+), and Mg(2+) in gentamicin (GM)-treated rats. Male Wistar rats were injected with GM (40 or 80 mg/kg/day for 7 days, respectively; GM-40 or GM-80). The expression of NHE3, Na-K-ATPase, NKCC2, ROMK, NCC, alpha-, beta- and gamma-ENaC, and CaSR was examined in the kidney by immunoblotting and immunohistochemistry. Urinary fractional excretion of Na(+), K(+), Ca(2+), and Mg(2+) was increased and urinary concentration was decreased in both GM-40 and GM-80 rats. In cortex and outer stripe of outer medulla (cortex) in GM-80 rats, the expression of NHE3, Na-K-ATPase, and NKCC2 was decreased; NCC expression was unchanged; and CaSR was upregulated compared to controls. In the inner stripe of outer medulla (ISOM) in GM-80 rats, NKCC2 and Na-K-ATPase expression was decreased, whereas CaSR was upregulated, and NHE3 and ROMK expression remained unchanged. In GM-40 rats, NKCC2 expression was decreased in the cortex and ISOM, whereas NHE3, Na-K-ATPase, CaSR, ROMK, and NCC abundance was unchanged in both cortex and ISOM. Immunoperoxidase labeling confirmed decreased expression of NKCC2 in the thick ascending limb (TAL) in both GM-80- and GM-40-treated rats. Immunoblotting and immunohistochemical analysis revealed increased expression of alpha-, beta-, and gamma-ENaC in cortex in GM-80 rats, but not in GM-40 rats. These findings suggest that the decrease in NKCC2 in TAL seen in response to low-dose (40 mg/kg/day) gentamicin treatment may play an essential role for the increased urinary excretion of Mg(2+) and Ca(2+), and play a significant role for the development of the urinary concentrating defect, and increased urinary excretion of Na(+) and K(+). At high-dose gentamicin, both proximal and TAL sodium transporter downregulation is likely to contribute to this.

Animals↗
PubMed2006

Cyclooxygenase type 2 is increased in obstructed rat and human ureter and contributes to pelvic pressure increase after obstruction.

Prostanoids exert physiological effects on ureteral contractility that may lead to pressure changes and pain during obstruction. In the present study, we examined whether (1) obstruction changes the expression of the two cyclooxygenase (COX) isoforms, COX-1 and COX-2 in human and rat ureters and (2) administration of a selective COX-2 inhibitor influences the pelvic pressure change after experimental ureteral obstruction. Rats were subjected to bilateral ureter obstruction. Ureters were removed and dissected into a proximal dilated and distal non-dilated segment. RNA and protein were extracted and analyzed for cyclooxygenase expression by quantitative polymerase chain reaction and Western blotting. Human ureter samples were obtained from patients undergoing radical nephrectomy. Rat and human ureteral samples were processed for immunohistochemistry. COX-1, but not COX-2 mRNA, was readily detected in the normal rat ureter. COX-2 mRNA and protein expression was increased in the proximal dilated ureter compared to distal non-dilated ureter. This increased COX-2 expression was associated with increased urinary prostaglandin E2 (PGE2) excretion after release of obstruction. Immunohistochemistry showed increased COX-2 labeling in surface epithelium and smooth muscle layers in both rat and human obstructed ureters compared to control ureters. Furthermore, contractile PGE2-EP1 and thromboxane TP receptors were expressed in ureteral smooth muscle. Systemic treatment with the COX-2 selective inhibitor parecoxib (5 mg/kg/day) attenuated the pelvic pressure increase during obstruction. In summary, COX-2 expression is significantly increased in the ureteral wall in response to obstruction in the rat and human ureter and COX-2 activity contributes to increased pelvic pressure after obstruction.

Animals↗
PubMed2006

Biphasic changes of epithelial sodium channel abundance and trafficking in common bile duct ligation-induced liver cirrhosis.

We hypothesize that dysregulation of the epithelial sodium channel (ENaC) may be responsible for the increased sodium retention in liver cirrhosis. Liver cirrhosis was induced by common bile duct ligation (CBDL). We examined the abundance of ENaC subunits and type 2 isoform of 11beta-hydroxysteroid dehydrogenase (11betaHSD2) in the kidney by immunoblotting and immunohistochemistry at 6 or 8 weeks after operation. At 6 weeks, cirrhotic rats had developed ascites and displayed a positive sodium balance. The urinary sodium excretion and fractional excretion of sodium were decreased, while plasma aldosterone was unchanged. The abundance of ENaC subunits was not changed in the cortex and outer stripe of the outer medulla (OSOM). In contrast, immunoperoxidase microscopy revealed an increased apical targeting of alpha-, beta- and gammaENaC in late distal convoluted tubule, connecting tubule and collecting duct. Moreover, 11betaHSD2 abundance was decreased in the cortex/OSOM and inner stripe of the outer medulla. At 8 weeks, urinary sodium excretion and fractional excretion of sodium were not changed, while the plasma aldosterone level was decreased. The expression of ENaC subunits was decreased in the cortex/OSOM. Immunoperoxidase microscopy confirmed decreased expression of ENaC subunits, whereas subcellular localization was not changed. These results suggest that increased apical targeting of ENaC subunits and diminished abundance of 11betaHSD2 may contribute to promote sodium retention in the sodium-retaining stage of liver cirrhosis (at 6 weeks). The subsequent decreased expression and reduced targeting of ENaC subunits may play a role in promoting sodium excretion in the later stage of liver cirrhosis (at 8 weeks).

11-beta-Hydroxysteroid Dehydrogenase Type 2↗
PubMed2005

Magnesium depletion enhances cisplatin-induced nephrotoxicity.

PURPOSE: Nephrotoxicity and magnesium (Mg)-depletion are well-known side effects to cisplatin (CP) treatment. The purpose of this present study was to investigate the role of Mg on CP induced changes in renal function. CP induced renal dysfunction was achieved by treatment with CP or vehicle (2.5 mg/kg) once weekly for 3 weeks. Since the CP-induced renal damage, including tubular reabsorption defects, is most prominent within the outer medulla (OM), changes in the expression pattern of OM aquaporins and sodium transporters including the Na,K-ATPase (alpha-subunit), type III Na,H-exchanger (NHE3), aquaporin 1 (AQP1) and 2 (AQP2) and the Na,K,2Cl-cotransporter (NKCC2) were investigated by semi-quantitative Western blotting. EXPERIMENTAL DESIGN: Rats had access to either a diet with standard Mg or to a Mg-depleted diet. Cisplatin was administered to female Wistar rats once a week for 3 weeks according to four regimens: (1) Cisplatin 2.5 mg/kg body weight i.p., to rats on a diet with standard Mg, (2) Cisplatin 2.5 mg/kg body weight i.p., to rats on a diet with low Mg, (3) Isotonic NaCl 2.5 ml/kg body weight i.p., to rats on a diet with standard Mg, (4) Isotonic NaCl 2.5 ml/kg body weight i.p., to rats on a diet with low Mg. RESULTS: CP had no effect on plasma creatinine or urea in rats with standard Mg intake, but the expression of all five transporters was significantly reduced when compared to vehicle treated rats on standard Mg-intake. Vehicle treated rats on low Mg-intake had a significant reduction in the expression of Na,K-ATPase, NHE3 and NKCC2, but unchanged expression levels of AQP1 or AQP2 when compared to standard treated controls. Forty percent of the CP-treated rats on low Mg-intake died during the experiment and the remaining animals had marked increased plasma creatinine and urea. Furthermore, the Western blot analysis revealed an almost complete disappearance of all four transporters, suggesting a dramatic synergistic effect of CP and Mg-depletion on renal function including the expression pattern of outer medullary sodium transporters and aquaporins. CONCLUSIONS: This study indicates a substantial additive effect of Mg-depletion on cisplatin induced renal toxicity as evidenced by significant changes in plasma creatinine and urea, renal failure induced mortality and loss of renal transporters. This should give cause for concern since the nephrotoxicity observed during cisplatin treatment might be substantiated by the known Mg-loss associated with cisplatin treatment especially in patients suffering from intense gastro-intestinal side effects.

Animals↗
PubMed2005

Intrarenal blood oxygenation and renal function measured by magnetic resonance imaging during long-term cyclosporine treatment.

Treatment with cyclosporine (CsA) markedly affects the renin-angiotensin-aldosterone system in parallel with an increase in the net tubular reabsorption or a decrease in secretion. Since tubular reabsorption is closely linked to medullary oxygen consumption, the aim of the present study was to investigate the intrarenal oxygenation and renal function in response to CsA. Six mini Göttingen pigs were treated with CsA (10 mg/kg/d) for 6 months. The intrarenal oxygenation was indirectly measured as R2* obtained with a multiecho gradient-echo magnetic resonance imaging (MRI) sequence. Single-kidney renal blood flow (skRBF) was measured by a velocity-sensitive gradient-echo MRI sequence. Relative single-kidney glomerular filtration rate (rskGFR) was derived from the MRI time-activity curve in response to an intravenous bolus of Gd-DTPA (0.05 mmol/kg). The present study showed that administration of CsA increased the medullary R2* (23.1 Hz vs 19.0 Hz, P = .002), whereas R2* was slightly increased in the renal cortex (13.3 Hz vs 12.3 Hz, P = .012). In parallel, rskGFR increased significantly (47.2 mL/min vs 19.8 mL/min, P = .005) but skRBF was unchanged (197.6 mL/min vs 202.5 mL/min, P > .05). The increased R2* in the renal medulla indicated that CsA augments the tubular reabsorption of water, leading to increased oxygen consumption. The supply of oxygen to the kidney was, however, maintained during treatment with CsA as suggested by an unchanged renal blood flow. The increased tubular reabsorption was compensated for by an elevated glomerular filtration rate.

Animals↗
PubMed2005

Renal effects of hypotensive anaesthesia in combination with acute normovolaemic haemodilution with hydroxyethyl starch 130/0.4 or isotonic saline.

BACKGROUND: Hypotensive anaesthesia (HA) and acute normovolaemic haemodilution (ANH) are used separately to decrease per-operative blood loss. Reducing blood viscosity by adding ANH to HA may appear profitable in a situation with lowered perfusion pressure and concern about organ ischemia. The aim of this study was to clarify the influence of HA in combination with ANH using crystalloid or colloid as replacement fluid on renal function. METHODS: Hypotensive anaesthesia was induced in 11 patients referred to major spine surgery using sevoflurane in combination with fentanyl/remifentanil. Acute normovolaemic haemodilution was carried out by drawing venous blood into standard blood bags and replacing it by isotonic saline 0.9% (Group S) or HES 130/0.4 (Group V). Renal function was evaluated before, during and up to 8 h after hypotension as the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) by means of 51Cr-EDTA and 125I-Hippuran clearances. RESULTS: Lowering mean arterial blood pressure decreased GFR and ERPF in both groups. During hypotension ERPF was lower in Group S (n = 5) than Group V (n = 6). Renal function was normalized postoperatively. We found a positive but non-significant correlation between the relative GFR change and the duration of hypotension. CONCLUSION: In conclusion, our study demonstrated that renal function, assessed by GFR and ERPF, is transiently reduced during the combination of hypotensive anaesthesia and acute normovolaemic haemodilution. A colloid-based fluid regime (HES 130/0.4) used for haemodilution may preserve renal function to a greater extent than a crystalloid-based regime (0.9% saline).

Adult↗
PubMed2004

Transepithelial pressure pulses induce nucleotide release in polarized MDCK cells.

The release of nucleotides is involved in mechanosensation in various epithelial cells. Intriguingly, kidney epithelial cells are absolutely dependent on the primary cilium to sense changes in apical laminar flow. During fluid passage, the renal epithelial cells are subjected to various mechanical stimuli in addition to changes in the laminar flow rate. In the distal part of the collecting duct, the epithelial cells are exposed to pressure changes and possibly distension during papillary contractions. The aim of the present study was to determine whether nucleotide release contributes to mechanosensation in kidney epithelial cells, thereby establishing whether pressure changes are sufficient to produce nucleotide-mediated responses. Madin-Darby canine kidney (MDCK) cells grown on permeable supports were mounted in a closed double perfusion chamber on an inverted microscope. The intracellular Ca(2+) concentration ([Ca(2+)](i)) was monitored with the Ca(2+)-sensitive fluorescence probe fluo 4. Transepithelial pressure pulses of 30-80 mm Hg produced a transient increase in [Ca(2+)](i) of MDCK cells. This response is independent of the primary cilium, since it is readily observed in immature cells that do not yet express primary cilia. The amplitudes of the pressure-induced Ca(2+) transients varied with the applied chamber pressure in a quantity-dependent manner. The ATPase apyrase and the P2Y antagonist suramin significantly reduced the pressure-induced Ca(2+) transients. Applying apyrase or suramin to both sides of the preparation simultaneously nearly abolished the pressure-induced Ca(2+) response. In conclusion, these observations suggest that rapid pressure changes induce both apical and basolateral nucleotide release that contribute to mechanosensation in kidney epithelial cells.

Adenosine Triphosphate↗
PubMed2003

Quantitative assessment of Gd-DTPA contrast agent from signal enhancement: an in-vitro study.

Quantitative determination of in-vivo gadolinium diethylenetriamine-pentaacid (Gd-DTPA) concentration is attractive in various studies involving perfusion, tracer kinetics and permeability constants. Using a 1.5 T clinical system and a 7 T small-bore system, we evaluated a method for absolute determination of Gd-DTPA concentrations in plasma solutions. Different solutions of Gd-DTPA and (99m)Tc-DTPA were mixed in human plasma and concentrations in the range of 0-5.0 mmol/l (1.5 T system) or 0-3.0 mmol/l (7 T system) of Gd-DTPA were divided into thirteen tubes. All MRI measurements were carried out using conventional sequences (SE, FLASH and GRASS). The MR measured intensity was converted to Gd-DTPA concentration by mathematical interpretation of the sequences. All MRI sequences showed, that the measured concentrations of Gd-DTPA revealed a slight non-linear difference compared with the calculated Gd-DTPA concentrations determined by the plasma (99m)Tc-DTPA using gamma counting. This non-linearity was most pronounced at high Gd-DTPA concentrations, suggesting that the discrepancy could be a result of an increased plasma relaxivity at higher concentrations. Adjustment of measured Gd-DTPA concentration was therefore performed using a selected power function, A[Gd-DTPA](a), which yielded the best linear relationship. Regression analysis showed that the scaling constant (A) varied from 0.11 to 97.45 and the power constant (a) varied from 0.83 to 1.6. Based on these constants, the MRI measured concentrations of Gd-DTPA did not differ from the calculated concentrations of Gd-DTPA obtained from reference measurements of (99m)Tc-DTPA. In the 1.5 T system, a linear relationship (r(2) > or = 0.95) was demonstrated in the range of 0-5.0 mmol/l Gd-DTPA, and in the 7 T system, a linear relationship (r(2) > or = 0.92) was demonstrated in the range of 0-3.0 mmol/l Gd-DTPA. Additionally, the effect of signal-to-noise on measured concentrations of Gd-DTPA was simulated using MR data of the mixed solutions of Gd-DTPA in plasma and the analytical expression of the pulse sequences. The simulations showed that the concentrations were most sensitive to noise in the GRASS sequence. In conclusion, this study demonstrates a novel approach to quantify accurately the Gd-DTPA concentration directly from MRI signal data using different routine sequences.

Blood↗
PubMed2003

Renal function may not be restored when using decreasing differential function as the criterion for surgery in unilateral hydronephrosis.

OBJECTIVE: To evaluate the use of decreasing differential function (DF) as an indication for surgery in children with congenital hydronephrosis followed according to a flow chart with repeated renography and ultrasonography. PATIENTS AND METHODS: The hospital records of consecutive children (0-12 years old) who underwent an Anderson-Hynes pyeloplasty between 1993 and 2000 were reviewed. Follow-up was recommended according to a flow chart, with isotope renography and ultrasonography at 1, 3 and 6 months, and at 1 (2), 3 and 5 years of age. The diagnosis and follow-up were often at the referring hospital. The criteria for surgery included a decrease in renographic DF of > 10% of DF, and a DF of < 42%, breakthrough pyelonephritis despite antibiotic prophylaxis, pain or an anterior-posterior pelvic diameter of > 50 mm. RESULTS: Fifty-two children with unilateral hydronephrosis were included; eight had surgery because of decreasing DF of the hydronephrotic kidney. Seven children had a prenatal diagnosis. Only one of these eight children was managed according to the recommended procedures for follow-up. In two and possibly three children there was significant irreversible kidney damage since the initial renography before surgery. In one child the initial renography was at 15 months and the DF was < 10%. There was a functional improvement after surgery in three children. CONCLUSION: Few children undergo surgery for decreasing DF of the hydronephrotic kidney in this study. Failure to adhere to the follow-up schedule was common; this may jeopardize kidney function when using decreasing DF as a criterion for surgery. Therefore, not complying (by medical staff or the patient) with the follow-up should be considered when using expectant management for asymptomatic hydronephrosis. The serious consequences for renal function of not complying with follow-up can be avoided by surgery if the patient risks renal functional deterioration, by close cooperation with medical staff at referring hospitals, and by close follow-up at an early age with renography and ultrasonography.

Child↗
PubMed2003

Increased urinary excretion of aquaporin 2 in patients with liver cirrhosis.

BACKGROUND AND AIM: Water retention is a major clinical problem in patients with liver cirrhosis. Recent research suggests that renal aquaporins may be pathophysiologically involved in this condition. The aim of the present cross sectional study of patients with liver cirrhosis was to determine if 24 hour urinary excretion of renal aquaporin 2 (AQP2) differed from that of healthy control subjects and if such excretion was related to the severity of liver disease and to the patient's water balance. RESULTS: Twenty four hour urinary excretion of AQP2 and free water clearance were measured in 33 stable cirrhosis patients on usual medication and in eight healthy subjects. AQP2 excretion, quantitated by immunoblotting, was eight times higher in cirrhosis patients than in controls (0.167 (0.270) U/day v 0.021 (0.017); p<0.05). Stratification according to clinical manifestations (Child- Pugh classes) revealed that it increased with the clinical severity of cirrhosis (class A 0.04 (0.04); class B 0.09 (0.16); class C 0.31 (0.35); p<0.05) but was not related to liver function, as measured by galactose elimination capacity. Excretion correlated inversely with free water clearance (rho=-0.57, p<0.01). It was higher in patients with oesophagogastric varices but not in those with ascites. Plasma vasopressin concentrations were not related to AQP2 excretion and there was no relation to dose or type of diuretic treatment. CONCLUSIONS: Urinary AQP2 excretion was increased in patients with cirrhosis. Moreover, urinary AQP2 excretion increased with severity of cirrhosis in parallel with impairment of free water clearance. This suggests a functional association between increased AQP2 excretion and increased renal reabsorption of water in cirrhosis.

Adult↗
PubMed2002

Severe partial ureteric obstruction in newborn rats can produce renal dysplasia.

OBJECTIVE: To investigate whether partial unilateral ureteric obstruction (PUUO) produces renal dysplasia in newborn rats. MATERIALS AND METHODS: Left mild (in 31) or severe (in 34) PUUO was induced in 2-day-old rats by embedding a quarter or two-thirds of the ureter into the psoas muscles, respectively. Sham-operated control rats (36) were assessed in parallel. Kidney morphology, renal parenchymal weight and histology were examined 24 weeks and 30 months afterward. RESULTS: There was significant pelvic dilatation in all obstructed kidneys; four kidneys were dysplastic in those severely obstructed, with a significant decrease in renal volume. There were three dysplastic kidneys after 6 months and one at 30 months. The in vitro dysplastic kidney weight was 36% of the control kidneys. Microscopy showed primitive glomerular and tubular structures, with renal parenchymal developmental disorganization and marked fibrosis. The glomeruli, tubules and collecting ducts were deficient in number and had often undergone cystic changes. Columnar tubular epithelium and peritubular mesenchymal collars were present. There was no renal dysplasia in the mildly obstructed and sham-operated rats. The parenchymal weight of the kidneys contralateral to the dysplastic kidneys was significantly higher than in the controls (P < 0.001). CONCLUSIONS: Severe PUUO can produce renal dysplasia in newborn rats. However, only 12% with severe obstruction had renal dysplasia, indicating that the cause of renal dysplasia might also be related to other factors.

Animals↗
PubMed2002

Renal water and sodium handling during gradated unilateral ureter obstruction.

OBJECTIVE: Unilateral complete obstruction of the ureter (UUO) is associated with characteristic changes in renal function. To improve the understanding of how urine concentration directly is affected by changes in pelvic pressure, changes in renal salt and water handling along the nephron and collecting duct were examined. MATERIAL AND METHODS: Pelvic pressure was raised stepwise using an adjustable lever inserted in the right ureter. Urine samples were collected from the tip of the catheter by way of an overflow system. Water and sodium handling in the distal and proximal tubules were measured by the lithium clearance technique. Renal blood flow (RBF) was measured with implanted ultrasonic flow probes. Catheters were placed in both renal veins and glomerular filtration rate (GFR) and filtration fraction were calculated using renal extraction of (51)Cr-EDTA independent of urine sampling. RESULTS: The sequence of changes for each parameter is provided. The parameters did not show a uniform pattern from which specific threshold values could be derived. However, the mean value of the following parameters were markedly changed at specific pressures: (1) at 10 cm H(2)O ipsilateral urine output decreased rapidly and distal absolute reabsorption of sodium (DAR(H2O)) decreased, (2) at 20 cm H(2)O GFR started to decline rapidly, (3) at 30 cm H(2)O urine output was impaired, and (4) at 40 cm H(2)O proximal absolute reabsorption of water (PAR(H2O)) showed a decreasing tendency in all pigs together with impairment in tubular sodium handling. Furthermore, free water clearance was slightly impaired (-0.26 +/- 0.15 at baseline and -0.15 +/- 0.08 ml/min at maximum pressure) and ipsilateral RBF decreased from 171.1 +/- 12.4 ml/min at baseline to 136.3 +/- 12.3 ml/min at ureteral pressure of 80 cm H(2)O (p < 0.05). Consistent with that, ipsilateral renal vascular resistance increased with increasing pressure in the renal pelvis. CONCLUSION: Water reabsorption and sodium handling is progressively impaired with increasing pelvic pressure. GFR and RBF are reduced in parallel. The study shows that the kidney responds to ureteral obstruction is unique and individual.

Animals↗
PubMed2001

Reduced renal vascular resistance in response to verapamil during gradated ureter obstruction in pigs.

Unilateral ureteral obstruction (UUO) is associated with reductions in ipsilateral renal blood flow (RBF) and glomerular filtration rate (GFR) caused by an active preglomerular vasoconstriction, where angiotensin II (ANGII) may be an important mediator. Calcium-channel blockers preferentially dilate preglomerular vessels and abolish the vasoconstrictor actions of ANGII in preglomerular arterioles of the hydronephrotic rat kidney. In this study, we, therefore, examined the effects of the calcium-channel blocker verapamil (3.65 microg/kg per minute i.v.) on RBF, GFR and renal vascular resistance (RVR) in our pig model with UUO, where ultrasonic flow probes are mounted on each renal artery and catheters placed in the abdominal aorta and both renal veins. Verapamil treatment was associated with a 34% reduction in ipsilateral RBF (from 182.6 +/- 20.5 ml/min to 120.6 +/- 12.2 ml/min, P < 0.001), which was similar to the 27% reduction in ipsilateral RBF in controls (from 194.6 +/- 13.1 ml/min to 140.6 +/- 15.2 ml/min, P < 0.001). Ipsilateral GFR was reduced by 70% in the verapamil-treated pigs (from 29.0 +/- 2.6 to 8.5 +/- 0.9 ml/min, P < 0.001) and by 73% in control animals (from 29.2 +/- 3.1 to 7.6 +/- 2.1 ml/min, p < 0.001). However, the increase in RVR was significantly attenuated in the verapamil-treated pigs. Ipsilateral RVR increased by 19% in the verapamil-treated pigs (from 0.585 +/- 0.076 to 0.726 +/- 0.081 mmHg/min/ml, P < 0.05) compared with a 34% increase in control pigs (from 0.560 +/- 0.056 to 0.854 +/- 0.091 mmHg/min per milliliter, P<0.001), suggesting that an intact calcium-channel may be important for the increase in renal vascular resistance during unilateral ureter obstruction. In conclusion, the present study shows that verapamil is able to modulate the increase in renal vascular resistance in response to increased pelvic pressure.

Angiotensin II↗
PubMed2001

Physiology and pathophysiology of renal aquaporins.

The discovery of aquaporin-1 (AQP1) by Agre and associates answered the longstanding biophysical question of how water specifically crosses biological membranes. In the kidney at least 7 aquaporins are expressed at distinct sites. AQP1 is extremely abundant in the proximal tubule and descending thin limb and is essential for urinary concentration. AQP2 is exclusively expressed in the principal cells of the connecting tubule and collecting duct and is the predominant vasopressin-regulated water channel. AQP3 and AQP4 are both present in the basolateral plasma membrane of collecting duct principal cells and represent exit pathways for water reabsorbed apically via AQP2. Studies in patients and transgenic mice have shown that both AQP2 and AQP3 are essential for urinary concentration. Three additional aquaporins are present in the kidney. AQP6 is present in intracellular vesicles in collecting duct intercalated cells and AQP8 are present intracellularly at low abundance in proximal tubules and collecting duct principal cells but the physiological function of these 2 channels remain undefined. AQP7 is abundant in the brush border of proximal tubule cells and is likely to be involved in proximal tubule water reabsorption. A series of studies have underscored crucial roles of aquaporins for regulation of renal water metabolism and hence body water balance. Moreover it has become clear that dysregulation of aquaporins, and especially AQP2 is critically involved in many water balance disorders. Lack of functional AQP2 is seen in primary forms of diabetes insipidus, and reduced expression and targeting is seen in several diseases associated with urinary concentrating defects such as acquired nephrogenic diabetes insipidus, postobstructive polyuria, as well as acute and chronic renal failure. In contrast, in conditions with water retention such as severe congestive heart failure, pregnancy and SIADH both AQP2 expression levels and apical plasma membrane targetting is increased suggesting a role for AQP2 in the development of water retention. Continued analysis of the aquaporins is providing detailed molecular insight into the fundamental physiology and pathophysiology of water balance and water balance disorders.

Animals↗
PubMed2001

Renal function outcome in unilateral hydronephrosis in newborn pigs. II. Function and volume of contralateral kidneys.

PURPOSE: We evaluated the compensatory response of contralateral kidney growth and function in pigs with unilateral hydronephrosis. MATERIALS AND METHODS: Unilateral partial ureteral obstruction causing severe hydronephrosis was induced at age 2 days in 12 piglets, while 10 underwent sham operation. At ages 4, 12 and 24 weeks single kidney function was assessed using 99mtechnetium diethylenetriaminepentaacetic acid differential uptake on renography combined with the glomerular filtration rate estimated from the plasma clearance of 99mtechnetium diethylenetriaminepentaacetic acid. Kidney size was measured in parallel by magnetic resonance imaging. RESULTS: At 4 weeks the glomerular filtration rate and volume of the contralateral kidneys did not differ from those in controls, although obstructed kidney function was significantly decreased. At 12 weeks the mean glomerular filtration rate plus or minus standard error of mean of the contralateral kidneys significantly increased to 1.60 +/- 0.11 versus 1.33 +/- 0.11 ml. per minute per kg. (p <0. 05), whereas kidney volume did not differ from that in sham operated controls. At 24 weeks the glomerular filtration rate and volume of the contralateral kidneys did not differ from those in controls. Glomerular filtration rate and volume of the contralateral kidneys did not correlate at 4 weeks but they correlated at 12 and 24 weeks (r = 0.94 and 0.89, respectively). CONCLUSIONS: Initially kidneys contralateral to obstructed kidneys with decreased function had no increased growth or function. Furthermore, function and volume of the contralateral kidneys were not associated at the early age. Thus, the results of our study imply that determining the size (growth) or function of the contralateral kidney at an early age does not predict function decrease in a partially obstructed kidney in this pig model.

Animals↗
PubMed2001

Effects of centrally administered arginine vasopressin and atrial natriuretic peptide on the development of brain edema in hyponatremic rats.

OBJECTIVE: Centrally released arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) have been shown to participate in brain volume regulation. The aim of the present study was to evaluate the effects of centrally administered AVP and ANP on the time course of development of brain edema in vivo in hyponatremic rats, using diffusion-weighted magnetic resonance imaging. METHODS: We performed intracerebroventricular (ICV) administration of 120 microg AVP, 20 microg ANP, or physiological saline into the right lateral ventricle in 18 rats. Twenty-five minutes after the treatment, we induced systemic hyponatremia by the intraperitoneal administration of 140 mmol/L dextrose solution. Serial diffusion-weighted imaging scans were obtained up to 96 minutes after the start of the hyponatremia. Changes in the brain extra-to intracellular volume fraction ratio were estimated as changes in the apparent diffusion coefficient (ADC). RESULTS: No change in the ADC was observed after the ICV injection of saline or AVP. The onset of hyponatremia induced a rapid and marked ADC reduction in both groups, indicating an increased intracellular space. However, the ADC decrease became significantly more pronounced in the ICV AVP group (83.3+/-4.7% of baseline level, mean +/- standard deviation) than in the saline group (93.7+/-3.3% of baseline, P < 0.001) after 78 minutes of hyponatremia. The ICV injection of ANP induced a prompt ADC increase to 111.5+/-10.0% (P < 0.05) of the baseline level, indicating a rapid reduction in the intracellular compartment. In the initial phase of hyponatremia, the ADC values in the ANP group were consistently higher than those in the saline group, decreasing finally to 86.9+/-9.6% after 96 minutes of hyponatremia. CONCLUSION: Our findings demonstrate the opposite effects of AVP and ANP on the intracellular volume fraction of the brain during the development of cellular brain edema, with an immediate effect on ANP and a delayed effect on AVP. The results emphasize the direct effects of these hormones on the cellular volume regulatory mechanisms in the brain during the development of cerebral edema.

Animals↗