Renal clearance and isolated kidney perfusion techniques

Evaluating the nephrotoxicity of cytotoxic agents using a rat kidney perfusing model

The nephrotoxicity of a number of chemother apeutic drugs may be a great problem from the clinical point of view, especially under a high dose therapy. It has been shown that, under certain circumstances, the maximum dose of a cytotoxic agent is not administered by the tox icity in the bone marrow but by the renal toxic ity. The renal mechanisms of action of cytotoxic drugs are poorly understood. The kidney seems to be very sensitive to the actions of these substances. In addition, the kidney plays a spe cial role in comparison with other organs be cause of the existence of an osmotic gradient in the renal medulla that results in a higher local concentration of systemically given cytotoxic drugs than in the remaining organism. The exper imental model of the isolated perfused rat kidney is a powerful tool to investigate the nephrotoxicity of chemotherapeutic agents. In this preparation, functional parameters can be changed in a con trolled manner, and systemic influences on renal function are eliminated.

Reference values and physiological characterization of a specific isolated pig kidney perfusion model

BACKGROUND

Models of isolated and perfused kidneys are used to study the effects of drugs, hazardous or toxic substances on renal functions. Since physiological and morphological parameters of small laboratory animal kidneys are difficult to compare to human renal parameters, porcine kidney perfusion models have been developed to simulate closer conditions to the human situation, but exact values of renal parameters for different collection and perfusion conditions have not been reported so far. If the organs could be used out of regular slaughtering processes animal experiments may be avoided.

METHODS

To assess renal perfusion quality, we analyzed different perfusion settings in a standardized model of porcine kidney hemoperfusion with organs collected in the operating theatre (OP: groups A-D) or in a public abattoir (SLA: group E) and compared the data to in vivo measurements in living animals (CON). Experimental groups had defined preservation periods (0, 2 and 24 hrs), one with additional albumin in the perfusate (C) for edema reduction.

RESULTS

Varying perfusion settings resulted in different functional values (mean +/- SD): blood flow (RBF [ml/min*100 g]: (A) 339.9 +/- 61.1; (C) 244.5 +/- 53.5; (D) 92.8 +/- 25.8; (E) 153.8 +/- 41.5); glomerular filtration (GFR [ml/min*100 g]: (CON) 76.1 +/- 6.2; (A) 59.2 +/- 13.9; (C) 25.0 +/- 10.6; (D) 1.6 +/- 1.3; (E) 16.3 +/- 8.2); fractional sodium reabsorption (RFNa [%] (CON) 99.8 +/- 0.1; (A) 82.3 +/- 8.1; (C) 86.8 +/- 10.3; (D) 38.4 +/- 24.5; (E) 88.7 +/- 5.8). Additionally the tubular coupling-ratio of Na-reabsorption/O2-consumption was determined (TNa/O2-cons [mmol-Na/mmol- O2] (CON) 30.1; (A) 42.0, (C) 80.6; (D) 17.4; (E) 23.8), exhibiting OP and SLA organs with comparable results.

CONCLUSION

In the present study functional values for isolated kidneys with different perfusion settings were determined to assess organ perfusion quality. It can be summarized that the hemoperfused porcine kidney can serve as a biological model with acceptable approximation to in vivo renal physiology, also if the organs originate from usual slaughtering processes.

Evaluation of renal functional parameters in different settings of isolated organ hemoperfusions

Isolated porcine kidneys are commonly used to study physiological and pathophysiological aspects of renal homeostasis but standardized evaluation procedures of renal function in this model do not exist so far. A double-logarithmical nomogram is established for filtration and reabsorption functions in isolated and hemoperfused porcine kidneys using different perfusion settings. Model validity was demonstrated by the levels of urine flow and sodium excretion showing expected alteration levels of lowering in the ADH-group and increasing in the furosemide-group of isolated kidneys. Creatinine-clearance values were in constant ranges within each specific perfusion group as indicated by the nomogram procedure. The present studies used a nomogram method to analyze the effects of different renal perfusion settings in a porcine model of kidney perfusion. The method may be of use to differentiate various kidney perfusion parameters both at the experimental and clinical levels.

Isolated rat kidney perfused with dextran and bovine serum albumin: A stable model for investigating renal drug handling

INTRODUCTION

The rat isolated perfused kidney (IPK) preparation is a very useful model for pharmacokinetic and pharmacologic studies. Bovine serum albumin (BSA) is the oncotic agent used most commonly in IPK models, but the protein is expensive and varies significantly in quality. The present study evaluated the use of dextran to replace a large proportion of BSA as the oncotic agent, to establish a more reliable and economic IPK model for pharmacokinetic studies.

METHODS

The right kidneys of male Sprague-Dawley rats were isolated and perfused in recirculating mode with Krebs-Henseleit pH 7.4 buffer containing amino acids, glucose and 65 g/l BSA (BSA group, n=11) or 6.5 g/l BSA plus 36 g/l dextran (dextran/BSA group, n=6). (14)C-Inulin was added to the perfusate to permit estimation of glomerular filtration rate (GFR). An antiviral guanosine analogue, AM188, was administered to the IPK perfusate to investigate its renal disposition. During the 130-min experimental period, urine was collected in 10-min intervals and perfusate was collected at the midpoint of these intervals.

RESULTS

The kidney functional parameters were generally better and more stable in the dextran/BSA IPKs when compared to the BSA group. At a similar perfusate flow rate, the IPKs in the dextran/BSA group exhibited lower renal artery perfusion pressure, a higher GFR, and more extensive tubular reabsorption of water, glucose, and sodium. These functional parameters were acceptable and stable throughout the whole experimental period in the dextran/BSA group. The renal clearance of AM188 was higher in the dextran/BSA group compared with that in the BSA group.

DISCUSSION

Using a large proportion of dextran and a small proportion of BSA as oncotic agent in perfusate provides an improved IPK preparation. This offers a reliable and economic rat IPK model for pharmacokinetic studies.

Impaired Renal Secretion of Substrates for the Multidrug Resistance Protein 2 in Mutant Transport–Deficient (TR−) Rats

ABSTRACT. Previous studies with mutant transport–deficient rats (TR−), in which the multidrug resistance protein 2 (Mrp2) is lacking, have emphasized the importance of this transport protein in the biliary excretion of a wide variety of glutathione conjugates, glucuronides, and other organic anions. Mrp2 is also present in the luminal membrane of proximal tubule cells of the kidney, but little information is available on its role in the renal excretion of xenobiotics. The authors compared renal transport of the fluorescent Mrp2 substrates calcein, fluo-3, and lucifer yellow (LY) between perfused kidneys isolated from Wistar Hannover (WH) and TR− rats. Isolated rat kidneys were perfused with 100 nM of the nonfluorescent calcein-AM or 500 nM fluo3-AM, which enter the tubular cells by diffusion and are hydrolyzed intracellularly into the fluorescent anion. The urinary excretion rates of calcein and fluo-3 were 3 to 4 times lower in perfused kidneys from TR− rats compared with WH rats. In contrast, the renal excretion of LY (10 μM, free anion) was somewhat delayed but appeared unimpaired in TR− rats. Membrane vesicles from Sf9 cells expressing human MRP2 or human MRP4 indicated that MRP2 exhibits a preferential affinity for calcein and fluo-3, whereas LY is a better substrate for MRP4. We conclude that the renal clearance of the Mrp2 substrates calcein and fluo-3 is significantly reduced in TR− rat; for LY, the absence of the transporter may be compensated for by (an)other organic anion transporter(s). E-mail: R.Masereeuw@ncmls.kun.nl

Brain natriuretic peptide increases urinary albumin and alpha-1 microglobulin excretion in Type 1 diabetes mellitus

Atrial natriuretic peptide (ANP) increases urinary albumin excretion in Type 1 diabetes mellitus (DM). Brain natriuretic peptide (BNP) is structurally and functionally related to ANP, but its effect on urine albumin excretion rate (UAER) is unknown.

AIMS

To compare the albuminuric effects of intravenous infusion of ANP and BNP, and to assess the effect of both peptides on tubular protein excretion.

METHODS

Eight subjects with Type 1 DM were randomised to a three leg, double blind, and placebo controlled study. On each study day, subjects were euglycaemic clamped and subsequently water loaded (20 mL/kg orally, plus urine losses) to steady state diuresis. When in steady state, creatinine clearance was estimated in three separate 1 hour periods. At the end of the first period, a 1 hour intravenous infusion of either placebo, ANP 0.025 microg/kg/min, or BNP 0.025 microg/kg/min was administered. There followed a 1 hour recovery period. Urine was collected at 15 min intervals for estimation of urine albumin (ACR) and alpha1 microglobulin creatinine ratio (MCR). Results were analysed by anova.

RESULTS

Creatinine clearance was similar on the three study days, and was unaltered by any infusion. ACR was unaltered by placebo (1.3 +/- 0.5-1.2 +/- 0.4 mg/mmol, mean +/- SD, p = 0.81), but increased compared to placebo with infusion of both ANP (1.2 +/- 0.4-9.8 +/- 8.4 mg/mmol, P = 0.0004), and BNP (1.1 +/- 0.4-13.4 +/- 8.6 mg/mmol, P = 0.0001). The MCR was unaltered by placebo infusion (P = 0.89), but increased compared with placebo after infusion of ANP (5.4 +/- 0.9-12.3 +/- 4.2 mg/mmol, P < 0.0001), and BNP (5.4 +/- 0.8-12.1 +/- 2.5 mg/mmol, P < 0.0001).

CONCLUSIONS

Intravenous infusion of BNP and ANP both increase the urine excretion of albumin and the tubular protein alpha1 microglobulin, independent of creatinine clearance.

Enhanced albuminuric response to atrial natriuretic peptide in normoalbuminuric patients with Type 1 diabetes mellitus--a pilot study

AIMS

To ascertain whether intravenous infusion of atrial natriuretic peptide (ANP) can induce microalbuminuria in patients with Type 1 diabetes mellitus (DM), as already demonstrated in patients with microalbuminuria, and to compare the albuminuric response to ANP infusion in Type 1 DM and a matched group of healthy non-diabetic controls.

METHODS

Eight normoalbuminuric DM patients participated in a three limb, randomized, double-blind, placebo-controlled study. Subjects were kept euglycaemic by insulin infusion, and subsequently water-loaded (20 ml/kg orally plus urinary losses). When in steady state, a 30-min infusion of either placebo, ANP 0.025 mg x kg(-1).min(-1) or ANP 0.05 mg x kg(-1) x min(-1) was administered intravenously. Urine was collected every 15 min for 90 min for the estimation of albumin-creatinine ratio (ACR). In addition, eight nondiabetic volunteers received a single infusion of ANP 0.025 mg x kg(-1) x min(-1).

RESULTS

ACR was unaltered by placebo in DM subjects (1.4 +/- 0.7-1.7 +/- 1.1 mg/mmol, mean +/- SD, ANOVA, P > 0.9), and by low dose ANP in controls (1.4 +/- 0.9-2.6 +/- 1.9 mg/mmol, P = 0.4). ACR increased with low dose ANP (1.3 +/- 0.5-14.6 +/- 13.6 mg/mmol, P = 0.02), and high dose ANP (1.3 +/- 0.7-26.4 +/- 31 mg/mmol, P = 0.01) in DM subjects. The ACR response to low dose ANP was greater in the DM than control subjects (P = 0.02).

CONCLUSIONS

ANP increases urine albumin excretion rate in normoalbuminuric Type 1 DM patients, and this effect is more pronounced than in healthy volunteers.

Urinary excretion of urodilatin is increased during pressure natriuresis in the isolated perfused rat kidney

The findings about mechanisms regulating production and excretion of urodilatin [ANP-(95-126)], a member of the atrial natriuretic peptide (ANP) family, are controversial. To elucidate a possible relationship between arterial blood pressure and renal urodilatin excretion, we studied the effects of different perfusion pressures on urine flow (UV), urinary sodium (U(Na)V), urinary potassium (U(K)V), and urodilatin excretion (U(URO)V), and the concentration of urodilatin in the perfusate (P(URO)) of isolated perfused rat kidneys. Kidneys were perfused for 180 min with constant perfusion pressures (80 and 120 mmHg, respectively; each, n = 4) in a closed circuit system. Samples of urine and perfusate were taken every 30 min. Mean UV, U(Na)V, U(K)V, and U(URO)V values were significantly higher with a perfusion pressure of 120 mmHg than with 80 mmHg, whereas P(URO) did not change significantly. Serial measurements revealed no direct relation of U(URO)V with either U(Na)V or UV. This suggests that renal perfusion pressure is a determinant of U(URO)V and that urinary and venous effluent concentrations of urodilatin (probably production) are not coupled directly and that U(URO)V and U(Na)V may dissociate during acute variations of sodium excretion and UV.

Extravasation of macromolecules

Macromolecules can extravasate across the normal endothelium by transcapillary pinocytosis as well as by passage through interendothelial cell junctions, gaps or fenestrae. The main biological factors that control extravasation of a solute include regional differences in the capillary structures, the disease state of the organ or tissue, and the rate of blood and lymph supply. Physicochemical properties that are of profound significance in the extravasation of macromolecules are molecular size, shape, charge and hydrophilic/lipophilic balance (HLB) characteristics. Extravasation of small drugs, proteins, oligonucleotides and genes can be controlled by conjugating or forming complexes with macromolecular carriers. This requires a thorough understanding of the relationship between the chemical structures, physicochemical properties and the pharmacokinetics of both carrier and active molecules. This review article discusses the extravasation of macromolecules from the view points of pharmacokinetics and drug delivery systems, with the main emphasis on the extravasation across the liver, kidney and tumor capillaries.

Peptide YY receptor distribution and subtype in the kidney: effect on renal hemodynamics and function in rats

This study characterizes the location and subtype of peptide YY (PYY) receptors in rat and rabbit kidney and the effect of PYY on renal function and renal hemodynamics in rats. Receptor autoradiography performed on kidney sections revealed a dense concentration of specific high-affinity binding sites [dissociation constant (Kd) = 0.7 +/- 0.1 nM] in the papilla of the rat, as well as cortical and papillary binding in the rabbit (papilla, Kd = 1.6 +/- 0.6 nM) and some medullary binding in both species. In the rat papilla, neuropeptide Y (NPY) and the Y1 agonist [Leu31,Pro34]NPY competed with PYY for binding (Kd = 1.1 +/- 0.4 nM and 1.6 +/- 0.5 nM, respectively), but NPY-(13-36) (Y2 agonist) and pancreatic polypeptide (PP, Y4 agonist) were without effect, demonstrating that the PYY receptor in the rat papilla is of the Y1 subtype. In the rabbit papilla, NPY and NPY-(13-36) competed with PYY (Kd = 0.5 +/- 0.1 and 3.1 +/- 0.6 nM, respectively), but [Leu31,Pro34]NPY and PP were without effect, evidence that the PYY receptor in the rabbit papilla is of the Y2 subtype. Infusion of PYY into rats (47 pmol x kg(-1) x min[-1]) increased mean arterial pressure (103 +/- 6 to 123 +/- 8 mmHg) and decreased renal plasma flow (13 +/- 1.8 to 8.4 +/- 2.1 ml/min) but produced no significant change in glomerular filtration rate or sodium excretion. Injection of PYY or angiotensin II directly into the renal artery caused a dose-related vasoconstriction, which was less intense but of longer duration for PYY than for angiotensin II. These results show that receptors for PYY are widely distributed in the kidney and that exogenously administered PYY causes renal vasoconstriction and may influence renal sodium excretion.

Effects of low and high density lipoproteins on renal cyclosporine A and cyclosporine G disposition in the isolated perfused rat kidney

PURPOSE

This study investigated the effects of low (LDL) and high density lipoproteins (HDL) on renal cyclosporine A (CsA) and cyclosporine G (CsG) disposition in the isolated perfused rat kidney model.

METHODS

Kidneys were perfused with CsA or CsG in perfusion medium containing 6% protein, bovine serum albumin only (BSA) (Control), LDL (200 mg/dl) and BSA, or HDL (200 mg/dl) and BSA. In vitro protein binding studies were conducted with CsA and CsG in the same media.

RESULTS

The unbound fractions (fu) of CsA and CsG were significantly reduced with LDL and HDL in the perfusion media. In the presence of LDL, fu for CsA and CsG was 3.9% and 5.9%, respectively. With HDL, fu was 2.1% for CsA and 1.8% for CsG. fu for the controls was 14.7% for CsA and 11.9% for CsG. Renal clearance (CLR) of CsA and CsG was significantly reduced when perfused with perfusion medium containing LDL and HDL. LDL and HDL had similar effects on reducing CsA and CsG CLR, and were approximately four-fold lower when compared to controls (approximately 0.006 Vs. 0.023 ml/min). Renal CsA and CsG tissue (whole organ, cortex and medulla) concentrations were lower than corresponding controls when perfused with LDL or HDL.

CONCLUSIONS

The interaction of CsA and CsG with LDL and HDL significantly reduced the CLR and extent of renal tissue distribution of both compounds.

Influence of trifluoperazine and verapamil on the isolated perfused rat kidney

1. Isolated rat filtering kidneys were perfused with Ringer bicarbonate solutions containing either trifluoperazine (TFP, 50 microM) or verapamil (VER, 100 microM) to prevent tissue dysfunctions observed during perfusion. 2. Water, sodium and chloride kidney contents diminished under both treatments as compared with control preparations, and potassium content increased. 3. When albumin concentration was increased (10 g%) in the perfusion medium (nonfiltering kidney preparation) these effects of TFP or VER were not observed. 4. Lipid peroxidation and LDH release diminished significantly under 50 microM TFP but only slightly under 100 microM VER.

Role of perfusate hydrogen ion activity in kallikrein release from isolated rat kidneys

The present experiments were performed to investigate whether renal kallikrein release by isolated perfused rat kidneys correlates with acid-base-related parameters. Kallikrein excretion per millilitre of glomerular filtrate was inversely correlated with perfusate pH (r = -0.49, P < 0.001) and HCO3- concentration (r = -0.46, P < 0.005). A direct relationship between kallikrein excretion per millilitre of glomerular filtrate and urinary Na+/K+ ratio was found (r = 0.59, P < 0.001). Some 86% of the variability (F ratio 110, P < 0.00001) of urinary kallikrein activity was attributable to the perfusate pH and the urinary cation ratio. Therefore, urinary kallikrein activity was highly correlated with perfusate H+ activity corrected by the urinary Na+/K+ ratio (r = 0.92, P < 0.0001). Kallikrein secretion into the distal tubular fluid appears to be regulated by blood H+ activity, and modulated by factors that affect the distal Na+ and K+ handling. The HCO3 - excretion rate was inversely correlated with the urinary kallikrein activity (r = -0.62, P < 0.001). This finding confirms previous data from the author's laboratory showing a kallikrein involvement in the regulation of HCO3- secretion in rats and rabbits. Kallikrein probably transduces the sensing of interstitial fluid H+ activity by the connecting tubule cells into an appropriate translocation of HCO3- or H+ to the tubular lumen by the intercalated cells.

Relationship between the diuretic effect of radiocontrast media and their ability to increase renal vascular resistance

The relationship between diuresis and natriuresis induced by radiocontrast media (RCM) and their renal haemodynamic effects were investigated. The effects of the iso-osmolar iotrolan and the hyperosmolar diatrizoate on the renal vascular resistance (RVR) were studied in the filtering and non-filtering variants of the isolated perfused rat kidney (IPRK) preparation. In the non-filtering model, no tubular regulatory process can be activated. The effect of diatrizoate on the RVR of the filtering IPRK in the presence of fursemide (0.3 mmol l-1) an inhibitor of the tubuloglomerular feedback (TGF) was also investigated. There was no significant difference (p > 0.05) in the response of the filtering (n = 6) and non-filtering (n = 6) IPRK to iotrolan. The induced reduction in the renal perfusate flow (RPF) by iotrolan was 20.5 +/- 3.05% and 22.9 +/- 3.03%, respectively. The reduction in the RPF which was observed with diatrizoate in the non-filtering IPRK (n = 5, 17.5 +/- 3.04%) was significantly less (p < 0.05) in comparison to that of the filtering IPRK (n = 6, 26.9 +/- 4.28%). In the frusemide experiments, a reduction in the RPF comparable to that of the non-filtering kidney was observed (n = 5, 13.7 +/- 4.34%). This study demonstrates that the renal vascular effect of diatrizoate is partially dependent on the TGF response. No tubular regulatory mechanism was accountable for the haemodynamic effect of iotrolan. The activation of the tubular response is osmolarity dependent.

Intrarenal dopamine participation in frusemide diuretic and natriuretic responses to frusemide

1. Dopamine (DA) involvement in the renal response to frusemide was analysed using the isolated perfused rat kidney preparation. Endogenous DA levels were increased through the infusion of its precursor levodopa (LD) (0.5 or 1 microM) whereas benserazide (50 or 100 microM), an inhibitor of the enzyme L-dopa-decarboxylase, was used to decrease DA synthesis. 2. Frusemide administration (0.3-20 nmols) induced a dose-dependent increase in fractional excretion of water (FE H2O), sodium (FE Na+) and glucose (FEG). FE Na+ elicited by the diuretic was enhanced 30-40% by 0.5 microM of LD (n = 5, P < 0.05), and 60-80% by LD 1 microM (n = 5, P < 0.05). FE H2O produced by the diuretic was enlarged 80-100% by 0.5 microM (n = 5, P = 0.05), and 130-170% by 1 microM of LD (n = 5, P < 0.01). The increase produced by both concentrations of LD on FEG was 200% for the lowest dose of the diuretic (n = 5, P < 0.01), and 90% for the highest (n = 5, P < 0.05). 3. Benserazide (BZ) (100 microM) decreased the F.E. Na+ induced by frusemide (n = 5, P < 0.05) by 32-42%, and completely abolished frusemide effects on FE H2O and FEG (n = 5). 4. In conclusion, our results suggest that endogenous dopamine participates in the frusemide-induced diuresis and sodium excretion within the kidney, and that the participation of extrarenal factors is not essential for this effect. Dopamine may be involved in frusemide-induced inhibition of proximal sodium reabsorption.

Existence of two pathways for the endocytosis of epidermal growth factor by rat liver: phenylarsine oxide-sensitive and -insensitive pathways

The effect of phenylarsine oxide (PAO) on the internalization rate of epidermal growth factor (EGF) was investigated using perfused rat liver and isolated rat hepatocytes. In perfused liver, a tracer concentration of 125I-EGF alone or with excess unlabeled EGF (20 nM) was perfused and the internalization rate constants (kint) were measured. In the absence of PAO, kint values did not differ significantly for either dose condition. However, with the addition of PAO to the perfusate, the kint value dropped to 4% of that of the control at the low concentration of EGF, while dropping to only 40% of that of the control at the high concentration of EGF. These results suggest the existence of a PAO-insensitive internalization pathway having a kint value comparable with that of the other pathway. Similar EGF concentration-dependent inhibition of 125I-EGF internalization caused by PAO was ascertained using isolated rat hepatocytes. PAO also decreased the cellular ATP content in isolated hepatocytes. However, when we lowered the cellular ATP content with rotenone, the cell-surface binding and internalization of EGF were comparable with the control levels. We concluded that there exist dual pathways for the internalization of EGF and that excess doses of EGF lead to EGF internalization not only through a PAO-sensitive pathway but also through a PAO-insensitive pathway, whereas at a tracer dose of EGF, the internalization occurs mainly via the PAO-sensitive pathway.

Renal receptors and effects of atrial natriuretic factor in compensatory renal hypertrophy

In the present study we investigated the in vivo and in vitro renal responsiveness to ANF, and the adaptation of ANF receptors in compensatory renal hypertrophy in the rat. One week after left nephrectomy (UNx), plasma levels of immunoreactive ANF, blood pressure (MAP), hematocrit (Hct), and urine flow rate (V) were unaltered compared to control (C) rats. Baseline GFR and potassium excretion (UKV) were significantly higher, and sodium excretion (UNaV) tended to be elevated in UNx rats. Administered ANF led to similar dose-related decreases in MAP and increases in Hct in UNx and C rats. However, at each dose of infused ANF, absolute values and the increase in GFR and UNaV were higher in UNx than in C rats. Hypertrophied (H) kidneys were removed from UNx and perfused in vitro to determine distribution and density of ANF receptors, responsiveness to ANF, and receptor-mediated organ clearance of 125I-ANF1-28. The density of ANF receptors in cortex, outer medulla, and papilla of H kidneys was not significantly different from that in C kidneys. In H isolated kidneys, ANF led to dose-related increases in GFR, V, UNaV, and UKV that were indistinguishable (P greater than 0.05) from those in C kidneys. Receptor-mediated organ clearance of 125I-ANF1-28 in isolated H kidneys was 2.8 +/- .02 ml/min, a value not significantly different (P greater than 0.05) from that in C kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Pressure independence of renin release by isolated kidneys of Lyon hypertensive rats

In the present work the influence of perfusion pressure on renal functions and renin release was studied before and after the blockade of thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors using isolated kidneys from 7-week-old genetically hypertensive (LH), normotensive (LN), and low blood pressure (LL) rats of the Lyon strain. Kidneys were single pass perfused with Krebs-Henseleit solution with a gelatine derivative (Polygeline) added as an oncotic agent. A servocontrolled system stabilized the renal perfusion pressure (RPP) at any chosen (+/- 1 mm Hg) level. In baseline conditions (RPP, 90 mm Hg), LH (n = 7) kidneys differed from LN (n = 6) and LL (n = 8) controls by increased vascular resistance, decreased glomerular filtration rate, and natriuresis. The LH kidney responses to stepwise changes in RPP (between 60 and 170 mm Hg) differed from those of LN and LL rats by a significantly lower perfusion flow, glomerular filtration rate, and natriuresis. Above all, the reduction in RPP, which induced a marked and highly reproducible renin release in LN and LL kidneys, was devoid of effects in LH kidneys. The blockade of TXA2/PGH2 receptors by AH23848 (4 x 10(-6) M) did not change the baseline (RPP, 90 mm Hg) functions of kidneys of the three strains. During changes in RPP, the responses of LN and LL kidneys were not modified, whereas LH kidneys exhibited significant increases in both glomerular filtration rate and natriuresis. Finally, AH23848 significantly decreased the renin release by kidneys of the three strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of angiotensin II-induced alterations in renal flow on excretion of cefonicid in isolated perfused rat kidneys

The effects of variations in renal perfusate flow on the excretion of cefonicid was examined in isolated perfused rat kidneys. Cefonicid, an expanded-spectrum cephalosporin, is primarily eliminated by active tubular secretion and is neither metabolized nor reabsorbed in the isolated kidney. We used angiotensin II (AII), a strong vasoconstrictor hormone of the afferent and the efferent arterioles in the kidney, to determine whether the renal and secretion clearances, as well as the excretion ratio (ER = CLR/[fu x GFR], where CLR is renal clearance, fu is the unbound fraction, and GFR is glomerular filtration rate), of this low-extraction compound can be altered by a decreased perfusion flow. Control studies were performed in the absence (n = 5) and presence (n = 4) of AII; cefonicid studies were performed in the absence (n = 4) and presence (n = 5) of AII. AII (1 to 4 ng/min) and cefonicid (5 to 10 micrograms/min) were infused into the perfusate. Cefonicid was assayed by high-performance liquid chromatography, and its protein binding was determined by ultrafiltration. AII decreased the perfusate flow rate and increased the renal vascular resistance and filtration fraction of the isolated kidney in the presence and absence of cefonicid. The glomerular filtration rate remained unchanged among the groups. The fractional excretion of glucose was low and steady, indicating a well-preserved tubular function. Although the unbound fraction was unchanged between treatments, the renal and secretion clearances and the excretion ratio of cefonicid were reduced by about 40% in the presence of AII (excretion ratios, 10.3 without AII versus 6.03 with AII). These results suggest that the altered clearance parameters of cefonicid are the result of a flow-induced change in the intrinsic secretory transport of the drug.

Renal tubular handling of p-aminohippurate and epidermal growth factor (EGF) in filtering and nonfiltering perfused rat kidneys

We examined the integrity of renal tubular function in filtering and nonfiltering isolated perfused rat kidneys by using p-amino-3H-hippurate (3H-PAH) and the multiple indicator dilution method with 14C-creatinine as a reference. The influx clearance (PSu,1) of unbound 3H-PAH was 0.37 and 0.38 ml/sec in the filtering and nonfiltering kidneys, respectively. The efflux rate constants were comparable between filtering and nonfiltering kidneys, while the sequestration rate constant in the filtering kidney was approximately three times larger than that in the nonfiltering kidney. These data suggest that the nonfiltering kidney maintains 3H-PAH transporting ability through the antiluminal plasma membrane. The renal handling of epidermal growth factor (EGF) by filtering and nonfiltering kidneys was compared. The ratio of the total uptake of tracer 125I-EGF over 20 min in the nonfiltering kidney to that in the filtering kidney was 0.8. This ratio was reduced to 0.2 when the kidneys were perfused with tracer 125I-EGF plus 20 nM EGF. Furthermore, the total uptake of tracer 125I-EGF in the nonfiltering kidney was reduced 20-fold in the presence of 20 nM unlabeled EGF. These findings suggest that the tubular uptake of tracer 125I-EGF by filtering kidney takes place mainly via the antiluminal plasma membrane and that this uptake is a saturable process.

Localization of epidermal growth factor (EGF) binding sites on antiluminal plasma membrane of rat kidney: autoradiographic study using nonfiltering perfused rat kidney

We previously demonstrated that the specific binding of EGF to the antiluminal plasma membrane was a prerequisite step for the renal uptake of EGF. In the present study, the localization of 125I-EGF binding sites on the antiluminal plasma membrane was investigated by tissue sampling and X-ray autoradiography in the nonfiltering kidney. The binding of 125I-EGF was recognized over the whole kidney and was highest in the inner medulla followed by the cortex and outer medulla. The binding of 125I-EGF in the nonfiltering kidney was completely inhibited in the presence of 20 nM unlabeled EGF, suggesting specific binding of 125I-EGF to its receptor. Further, we used a histologic tissue staining method to confirm the location of the 125I-EGF binding sites. Binding of 125I-EGF was demonstrated on the proximal straight tubules (PST), cortical collecting ducts (CCD), inner medullary collecting ducts (IMCD), and thin limb of Henle in the inner medulla (IMTLH). We found that the binding of 125I-EGF was high in the IMTLH. In addition, we determined the grain density both on the cell surface membrane and in the intracellular space of the proximal straight tubules, where the grain density on the antiluminal plasma membrane was approximately 50% that in the intracellular space at 20 min after the start of 125I-EGF perfusion, suggesting the internalization of 125I-EGF from the antiluminal plasma membrane to the intracellular compartment. In conclusion, the binding sites of 125I-EGF, which were accessible from the antiluminal side, were broadly distributed over the whole kidney and were most dense around the IMTLH.

Influence of the unbound concentration of cefonicid on its renal elimination in isolated perfused rat kidneys

The effect of variations in plasma protein binding on the renal excretion of cefonicid was assessed by using isolated perfused rat kidneys. Cefonicid exhibits preferential binding ex vivo to human serum albumin (HSA), as opposed to bovine serum albumin (BSA), and is eliminated mainly by tubular secretion, a process that was reported to be dependent on the total drug concentration. This contradicts previous studies with antimicrobial compounds and other drugs of low renal extraction in which the unbound drug concentration was shown to be the driving force for carrier-mediated tubular transport. To clarify this discrepancy, we performed perfusion studies by using 6% BSA at initial concentrations of 200 micrograms/ml (n = 6) and 20 micrograms/ml (n = 9) and in a combination of 4% BSA plus 2% HSA at initial concentrations of 200 micrograms/ml (n = 4). The excretion ratio [ER = CLR/(fu x GFR)] of cefonicid decreased with increasing unbound concentrations, whereas no apparent relationship with the total concentration was evident. At similar total concentrations of cefonicid, the renal clearance remained unchanged; the secretion clearance increased significantly in the 4% BSA-2% HSA experiments, reflecting the reduced unbound fraction and unbound drug concentration of cefonicid. The excretion ratio data were compatible with a model in which Michaelis-Menten kinetics were required to describe active transport and secretion was dependent on the unbound cefonicid concentration. As a result, changes in plasma protein binding as a result of drug interactions or disease states could significantly influence the tubular transport capability of compounds with low renal extraction.

Application of missing pulse steady state free precession to the study of renal microcirculation

Missing pulse steady state free precession (MP-SSFP), an extension of steady state free precession (SSFP), was evaluated for its ability to measure slow fluid flows. In experiments using flow phantoms, the MP-SSFP signal was sensitive to fluid velocities in the millimeters per second range. Isolated perfused rabbit kidneys were then used to determine if MP-SSFP could measure perfusion in a biological tissue. The signal intensities in the different anatomical regions of the kidney were observed to be related to the total flow to the organ. Furthermore, increasing the flow sensitivity of the pulse sequence by increasing the gradient strength resulted in decreases in the image signal intensity. The MP-SSFP signal was more sensitive to flow in the medulla than in the cortex. This can be related to slow flow sensitivity of MP-SSFP and the known differences in velocity profiles between these two regions. These results suggest that MP-SSFP may be a powerful tool for the noninvasive measurement of slow fluid flows in different regions of the kidney.

Effect of frusemide on lithium clearance and proximal tubular reabsorption in anaesthetized rats

1. In order to investigate the lithiuretic effect of frusemide, simultaneous measurements of fractional lithium excretion (FELi) and fractional fluid delivery to the end of the proximal convoluted tubules were made in Inactin-anaesthetized rats, first during a control period, then during intravenous infusion of frusemide at either 0.8 or 8.0 mg kg-1 h-1. Fluid balance was maintained by infusion of NaCl-KCl solution adjusted to match urinary excretion rates; measurements were made after urine flow had stabilized. 2. In time-control animals, which did not receive frusemide, no significant changes were observed in either FELi or fractional fluid delivery to the end of the proximal convoluted tubules (determined as the plasma/tubular fluid inulin concentration ratio, P/TFIn). 3. In animals given the high dose of frusemide, FELi increased from 0.22 +/- 0.02 (mean +/- S.E.M.) during the control period to 0.45 +/- 0.03 during frusemide infusion (P less than 0.001); this was accompanied by a modest increase in P/TFIn, from 0.43 +/- 0.02 to 0.51 +/- 0.02 (P less than 0.01). 4. In animals given the lower dose of frusemide, FELi increased from 0.21 +/- 0.01 to 0.37 +/- 0.01 (P less than 0.001). In this group, however, there was no discernible change in P/TFIn (0.43 +/- 0.02 vs. 0.44 +/- 0.01, not significant). 5. These results suggest that under control conditions a significant component of lithium reabsorption may occur beyond the proximal tubule, most likely in the loop of Henle.

Malignant cell attachment to endothelium of ex vivo perfused human umbilical vein. Modulation by platelets, plasma and fibronectin

The success of blood-born metastatic spread depends upon a key event: the tumor cell arrest and attachment to the host organ vasculature. In the present study, we have investigated interactions between several normal and cancer cell lines and vascular endothelium in a model of ex vivo perfusion of human umbilical vein. In this system, hydrodynamic parameters are monitored and endothelial cells are kept in their original environment known to modulate their phenotype. Metastatic tumor cell adhesion to the perfused endothelium was found to be significantly higher than that of normal cells tested. Platelets and soluble plasma factors including fibronectin promoted tumor cell arrest and adhesion to endothelium. Altogether our results indicate that the ex vivo perfusion of human umbilical vein allows the study of the interactions between malignant tumor cells, circulating plasma or blood cells and the endothelium during blood-born metastatic spread.

Haemodynamic effects of water-soluble contrast media on the isolated perfused rat kidney

The precise mechanism underlying the nephrotoxicity of radiocontrast media remains ill defined. In this study we have examined the direct effect of a wide range of low- and high-osmolar water-soluble contrast media (WSCM) on the vascular resistance of the isolated perfused rat kidney (IPRK). Water-soluble contrast media led to a significant fall in the renal perfusate flow and an increase in the renal vascular resistance (RVR). The magnitude of these haemodynamic changes was independent of the osmolality of the tested agents. This study shows a direct effect of WSCM on the vascular resistance of the isolated perfused rat kidney.

Receptor-mediated endocytosis of A14-125I-insulin by the nonfiltering perfused rat kidney

The mechanism of insulin uptake and/or degradation in the peritubular circulation of the kidney was investigated using nonfiltering perfused rat kidneys, in which glomerular filtration was sufficiently reduced. After perfusion of A14-125I-insulin in the nonfiltering kidney for designated intervals, the acid-wash technique was employed to separately measure the acid-extractable and acid-resistant A14-125I-insulin, which were quantitated by HPLC and TCA-precipitability. HPLC profiles showed that the nonfiltering kidney metabolizes A14-125I-insulin only to a small extent during 1-h perfusion, suggesting that the peritubular clearance of A14-125I-insulin was not due to extracellular degradation but for the most part to uptake by the kidney. Acid-extractable A14-125I-insulin rapidly increased with time and reached pseudo-equilibrium with perfusate at approx. 10 min, whereas acid-resistant A14-125I-insulin increased continuously. An endocytosis inhibitor, phenylarsine oxide, inhibited significantly the acid-resistant A14-125I-insulin with no change in acid-extractable A14-125I-insulin, suggesting that the peritubular uptake of A14-125I-insulin largely represents endocytosis of the peptide into the intracellular space. Moreover, both the acid-extractable and acid-resistant A14-125I-insulin were significantly decreased in the presence of unlabeled insulin (1 microM). These lines of evidence suggest that insulin is taken up by the nonfiltering perfused kidney via receptor-mediated endocytosis (RME), which possibly occurs at the basolateral side of renal tubular cells, and that the peritubular clearance of insulin is largely accounted for by this mechanism.

Isolated perfused rat kidney as a tool in the investigation of renal handling and effects of nonsteroidal antiinflammatory drugs

An isolated perfused rat kidney (IPK) preparation is described in which renal perfusion flow, perfusion pressure, urinary flow, urinary pH, and glomerular filtration rate (GFR) are recorded continuously during the perfusion experiment. The usefulness of this IPK system in studying the renal handling and the effects of non-steroidal antiinflammatory drugs (NSAIDs) is shown using salicyluric acid (SU), salicylic acid (SA), and naproxen (NA). Excretion of SU involves glomerular filtration, active secretion, and passive reabsorption. The excretion rates of SA and NA were both much lower than their filtration rate, indicating extensive reabsorption. All three drugs accumulate in the IPK but at different levels. SU accumulates much more than either SA or NA. The effects on renal function were different for the three drugs studied. SU had no effect on kidney function. SA perfusate concentrations greater than 100 micrograms/mL caused diuresis and natriuresis, while SA concentrations less than 100 micrograms/mL did not influence kidney function. NA perfusate concentrations ranging from 0.16 to 25 micrograms/mL caused a decrease in urinary flow and sodium excretion. Very high NA concentrations (greater than 500 micrograms/mL) caused an increase in urinary flow and sodium excretion. We conclude that the IPK is a suitable preparation for characterizing and comparing renal handling and effects of NSAIDs.

Metabolism of parathyroid hormone in isolated perfused rat kidney and liver combined

Metabolism of synthetic, intact, human parathyroid hormone (PTH) 10(-9) M was studied in a new experimental model using the isolated perfused rat kidney and liver combined. The combined organs cleared intact PTH significantly faster than the single kidneys (P less than 0.02) or livers (P less than 0.02), but not faster than the sum of the clearances in the single organs. The kidneys cleared intact PTH without accumulation of NH2-terminal, mid-molecule or COOH-terminal iPTH, and high-performance liquid chromatography (HPLC) studies did not reveal any PTH fragments. The livers cleared mid-molecule and COOH-terminal iPTH significantly slower (P less than 0.002) than intact PTH, and HPLC demonstrated generation of mid-molecule and COOH-terminal PTH fragments. The combined organs accumulated significantly less mid-molecule (P less than 0.001) and COOH-terminal (P less than 0.03) iPTH than the single livers, and HPLC demonstrated mid-molecule peaks that were smaller but not qualitatively different. In conclusion, the predominance of COOH-terminal PTH fragments in plasma may be maintained by differential clearance mainly in the liver, excessive accumulation being prevented by filtration in the kidneys.

Endocytosis and lysosomal hydrolysis of proteins in proximal tubules

The techniques and basic protocols described above can be readily reproduced by investigators with experience in perfusion of isolated nephron segments. They can be modified and adapted by the investigator to address specific issues. In particular, isolated perfused nephron segments have also been successfully used for elucidation of biochemical and morphological aspects of endocytosis and lysosomal hydrolysis of macromolecules, proteins, and polypeptides. The reader is directed to the references cited under Methodological Approaches in this chapter for a description of these techniques. Although studies on the endocytic uptake and metabolism of proteins and polypeptides using isolated perfused nephron segments have made significant inroads in our understanding of these fascinating and important biological processes, much remains to be learned. Hopefully, future uses of the technique will further advance our knowledge in this field.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.

Renal response to infusion versus repeated bolus injections of atrial natriuretic factor in man

In 7 healthy humans consuming a 170 mmol sodium diet the effect of the mode of administration of atrial natriuretic factor (human ANF 99-126) on renal function has been investigated, using conventional clearance studies during maximal water diuresis. ANF was administered as four repeated bolus (0.4 microgram/kg) injections and, after a 2-day interval, as a one-hour infusion (0.02 microgram/kg/min) preceded by a 0.4 microgram/kg bolus injection. In the two experiments ANF caused comparable elevations in glomerular filtration rate, free water clearance, and lithium excretion. No change in blood pressure or heart rate was observed in either study, and plasma renin activity and aldosterone fell by a similar extent. As expected, the time course of plasma ANF concentrations was markedly different during the two studies. It is concluded that with those doses of ANF the changes in renal haemodynamics and sodium handling were essentially similar after bolus injections and a constant infusion.

Potassium excretion in renal failure in the rat: the role of distal tubule flow and aldosterone

1. This study examines the contribution of an increased distal tubule flow and of aldosterone to the handling of a potassium load in conscious rats with renal failure induced by subtotal nephrectomy or by gentamicin on a control of high K+ diet. 2. Glomerular filtration rate was reduced by subtotal nephrectomy to 40% and by gentamicin treatment to 60% of control. Subtotal nephrectomy induced significant hypertrophy of glomeruli and proximal and distal tubules, but gentamicin did not. Both experimental groups had a normal iothalamate space and plasma potassium after a 20 h fast. 3. Two hours after an acute KCl load rats with renal failure excreted less potassium than control rats. There was also a lesser natriuretic effect of KCl in the renal failure groups. 4. A high K+ diet, given for 5-7 days, increased excretion of an acute KCl load in control rats and rats with renal failure. 5. (UNaV + UKV) was used as an estimate of distal tubule flow. Potassium excretion, related to distal tubule flow, was similar in the renal failure and control rats when on the same diet. This is consistent with potassium excretion being strongly, but not necessarily solely, dependent on distal flow. 6. Adrenalectomy reduced, and aldosterone restored, potassium excretion in the renal failure and control groups. This suggests a role for aldosterone in excretion of an acute potassium load with this degree of renal failure.

Interleukin-1 induces natriuresis in conscious rats: role of renal prostaglandins

The onset of infection is associated with increases in renal blood flow and sodium excretion. Our studies provide evidence that the natriuresis is mediated by stimulation of renal prostaglandin production by the cytokine, interleukin-1. A dose-dependent natriuresis and diuresis was elicited in conscious rats with bolus intravenous injections of human recombinant interleukin-1-beta (hrIL-1). Injection of 1.5, 3 and 24 micrograms hrIL-1 increased sodium excretion by 2.4 +/- 0.9 microEq/min, 4.0 +/- 0.8 microEq/min and 5.4 +/- 0.3 microEq/min, respectively. The natriuresis was preceded by a corresponding increase in urinary PGE excretion (80%, 110% and 296%, respectively). The natriuresis elicited by 3 micrograms hrIL-1 was independent of changes in glomerular filtration rate or effective renal plasma flow. IL-1 induced an increase in rectal temperature, (0.6 +/- 0.2 degrees C) and a modest increase in mean arterial pressure (12 +/- 3 mm Hg) within 10 minutes of injection. However, during the period of maximal natriuresis (40 to 100 min), blood pressure and rectal temperature were not significantly different from control. Pretreatment with the cyclooxygenase inhibitor, ibuprofen, significantly attenuated the natriuretic response and indomethacin completely abolished the natriuresis. These results identify IL-1 as a factor which stimulates renal PGE synthesis, and increases sodium excretion, independent of changes in glomerular filtration rate. We propose that IL-1-induced natriuresis may be a component of the overall acute phase response which is actively mounted by the host during infection.

Raised venous pressure: a direct cause of renal sodium retention in oedema?

Contemporary theories of oedema formation are often based on the idea that "effective" blood volume is reduced, and that sodium retention and oedema are a result of the kidney responding, as in haemorrhage, to a perception by receptors in the circulation that blood volume is inadequate. This idea has enhanced understanding of the pathophysiology of such conditions as cardiac failure and cirrhosis, but has obscured the fact that blood volume is almost always increased in oedematous states. Evidence is presented that an increase in renal venous pressure can cause sodium retention by a direct action on the kidney: a rise in venous pressure could thereby initiate a vicious circle by causing sodium retention, expansion of plasma volume, and further increase in venous pressure. This sequence of events may be crucial in the pathophysiology of cor pulmonale, and an exacerbating factor in other oedematous states.

Dose-response and time-response biochemical and histological study of potassium dichromate-induced nephrotoxicity in the rat

This study provides quantitative toxicological data on potassium dichromate-induced renal damage and considers the possible difficulties arising from the non-invasive in vivo assessment of renal damage, with particular attention to enzymuria. Renal damage induced in male Wistar rats by single sc injections of potassium dichromate was assessed 52 to 72 hr after doses ranging from 3 to 20 mg potassium dichromate/kg body weight and throughout a 9-day period following a dose of 20 mg potassium dichromate/kg. The earliest and most sensitive non-invasive functional change in the dose-response and time-response studies was an elevation in the rate of urinary excretion of protein. Evidence of tissue damage was observed with elevations in the urinary excretion rates of the brush border enzymes, gamma-glutamyltransferase, alkaline phosphatase and leucine aminopeptidase, the cytosolic enzymes, aspartate aminotransferase and lactate dehydrogenase and the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. Such changes occurred as early as the abnormal urinary protein excretion, but returned to control or sub-control values sooner. Urinary brush border enzyme excretion returned to control values within 48 hr following potassium dichromate injection, despite histological and histochemical evidence of extensive renal damage and renal dysfunction. Elevations in plasma aspartate aminotransferase and lactate dehydrogenase levels were observed, but histochemical and isoenzyme studies would be needed to determine the source of these increases. The simplest and most persistent indicators of renal damage were the urinary excretion of protein and N-acetyl-beta-D-glucosaminidase.

Alleviation of cyclosporine nephrotoxicity with verapamil and ATP-MgCl2. Mitochondrial respiratory and calcium studies

Although recent studies have shown that combined treatment with verapamil and ATP-MgCl2 (ATP) prevents cyclosporine (CyA)-induced nephrotoxicity, the mechanism of these effects remains unknown. To study this, rat kidneys were perfused at 100 mmHg for 100 minutes with Krebs buffer containing 7.5 g/dL of albumin and substrates. After an equilibration period of 30 minutes, 500 ng/mL CyA was added. In some experiments 1 microgram/mL verapamil was added 10 minutes prior to CyA and in others 2 mM ATP was added to CyA. At the end of the perfusion, cortical mitochondria (mito) were isolated and mito Ca2+ and Mg2+ (mumoles/g protein) and respiratory control ratios (RCR) were measured. In addition, total tissue Ca2+ and Mg2+ levels were measured. The results indicate that CyA treatment leads to an accumulation of mito Ca2+ and a decrease in ADP/O ratio. Simultaneous administration of ATP with CyA led to an increased mito Ca2+ accumulation and depressed RCR, which were corrected by verapamil pretreatment. The combination of verapamil pretreatment and ATP cotreatment with CyA increased tissue ATP levels from 0.8 +/- 0.4 (control) to 1.4 +/- 0.1 mumol/g. This pharmacologic regimen may prevent CyA-induced nephrotoxicity by preventing mito Ca2+ accumulation and by preserving mitochondrial respiratory function. This allows a more efficient generation of ATP and consequently preservation of renal function.