The basic requirements for the function of the isolated cell free perfused rat kidney

Quantitative Bioimaging of Platinum via Online Isotope Dilution-Laser Ablation-Inductively Coupled Plasma Mass Spectrometry

A new calibration strategy for elemental bioimaging based on online isotope dilution analysis (IDA) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) was developed and applied for the quantification of platinum in rat kidney tissues. A dry ¹⁹⁴Pt spike aerosol was added in a post-cell setup, and the natural ¹⁹⁴Pt/¹⁹⁵Pt isotope ratio of the sample aerosol from laser ablation was changed accordingly. Spike mass flow determination was carried out based on reversed IDA using a reference standard. Quantitative data obtained by the new approach correlated well with those obtained by external calibration when analyzing parallel tissue slices of rat kidney from cisplatin perfusion studies. The novel quantification approach is traceable to SI units, as IDA is an definitive method. Signal drifts are compensated as the second isotope acts as an internal standard.

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.

Demonstration of the existence of nitric oxide-independent as well as nitric oxide-dependent vasodilator mechanisms in the in situ renal circulation in near term pregnant rats

1. We have investigated the role of endogenous nitric oxide on renal vascular reactivity in late pregnancy in in situ blood perfused kidneys of alpha-chloralose anaesthetized Wistar-Kyoto rats. Nitric oxide synthesis inhibition was achieved by intravenous administration of NG-nitro-L-arginine or NG-nitro-L-arginine methyl ester. 2. Intra-arterial mean blood pressure was lower in pregnancy compared with nonpregnant controls. Following nitric oxide synthesis inhibition mean blood pressure increased in both pregnant and nonpregnant groups, but remained lower in pregnant animals. 3. Basal renal perfusion pressure was similar in pregnant and nonpregnant groups. Intravenous administration of Ng-nitro-L-arginine resulted in dose-dependent increases in renal perfusion pressure but responses were substantially depressed in pregnancy. 4. Renal vasoconstrictor responses to regional angiotensin II (AII) were decreased in pregnancy, whereas those to noradrenaline (NA) did not differ from nonpregnant controls. NG-nitro-L-arginine (5 mg kg-1) potentiated renal responses to regional AII and NA in both groups, but AII responses remained lower in pregnancy. Blunted renal AII responses in pregnancy were still evident following large doses of NG-nitro-L-arginine methyl ester (100 mg kg-1). 5. The results demonstrate that nitric oxide synthesis inhibition increases renal perfusion pressure to a lesser extent in pregnant compared with nonpregnant rats, and that reduced renal pressor responses to AII are still evident in pregnancy after nitric oxide synthesis inhibition. 6. These results suggest that although endogenous nitric oxide synthesis modulates renal vasoconstrictor responses in both pregnant and nonpregnant animals, this mechanism does not fully account for the blunted renal vasconstrictor responses to regional AII or nitric oxide inhibitors in near term pregnant rats. The nature of this important physiological vasodilator mechanism in pregnancy remains to be elucidated.

Modulation of c-fos and egr-1 expression in the isolated perfused kidney by agents that alter tubular work

The isolated perfused rat kidney provides a model of selective hypoxia to the medullary thick ascending limb. To investigate the relationship between immediate early gene expression and the extent of hypoxic damage, we determined expression of the immediate early genes (IEG) c-fos and egr-1 in isolated perfused kidneys during standard perfusion and after various measures shown previously to be protective. mRNA levels of c-fos and egr-1 were markedly increased in kidneys after 90 minutes of standard perfusion with Krebs-Henseleit buffer containing albumin. Gene expression was most prominent in the outer medulla followed by papilla and cortex, a pattern reflected by the immunohistochemical demonstration of a prominent accumulation of both egr-1 and c-fos polypetides mainly in the medullary thick ascending limb (mTAL). Protective measures known to minimize morphological damage to the mTAL, including hyperoncotic perfusion, perfusion with glycine, or perfusion with a mixture of amino acids, decreased mRNA levels of c-fos and egr-1 in the outer medulla (by 50% and 35%, respectively) and the papilla (by 60 and 30%, respectively). Renal cortex showed only minor changes. In contrast, prevention of tubular transport by perfusion with 1 mM ouabain increased mRNA levels of c-fos and egr-1 in the outer medulla by 100% and 60%, respectively. Ouabain also dramatically increased mRNA levels of both IEGs in two lines of cultured renal epithelial cells. Changes in the level and distribution of the protein products of these IEGs were not detectable in perfused kidneys by immunohistochemistry. Hypoxic injury of the kidney stimulates IEG expression even in the absence of reperfusion. Protection against hypoxic injury in the mTAL correlates with suppression of IEG mRNA levels when protection is provided by amino acids or hyperoncotic perfusion, but not when provided by inhibition of Na,K-ATPase, which stimulates IEG expression. We conclude that diminished IEG expression is not a necessary concomitant of protection against hypoxic injury.

Renal vasodilation to histamine in vitro: roles of nitric oxide, cyclo-oxygenase products and H2 receptors

The aim of this study was to evaluate the roles of nitric oxide (NO) and prostanoids in vasodilation to histamine in the preconstricted isolated perfused rat kidney. Kidneys were excised from Hypnorm/Hypnovel-anaesthetised Wistar rats and perfused at constant flow in vitro. Renal perfusion pressure was elevated similarly with methoxamine (3 microM) or modified Krebs Henseleit solution containing high KCl (30 mM) and vasodilation to histamine (10, 30 nmol) and papaverine (30, 100 nmol) was then examined before and during perfusion with the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 0.3 mM) or the cyclo-oxygenase inhibitor, indomethacin (10 microM). Furthermore, the vasodilator response to 30 nmol histamine was examined in the presence of the H2 receptor antagonist, ranitidine (0.1-10 microM). Vasodilation to histamine (10, 30 nmol) was found to be unaffected by L-NAME (0.3 mM) or indomethacin (10 microM), while ranitidine (0.1-10 microM) antagonised vasodilation to 30 nmol histamine with an estimated pA2 of 6.67. Vasodilation to histamine in the isolated perfused rat kidney is therefore probably independent of NO and prostanoids and mediated by H2 receptors.

In vitro nephrotoxicity of Russell's viper venom

To assess direct nephrotoxicity of Russell's viper venom (RVV; Daboia russelii siamensis), isolated rat kidneys were perfused in single pass for 120 min. Ten micrograms/ml and 100 micrograms/ml RVV were administered 60 minutes and 80 minutes, respectively, after starting the perfusion. Furthermore, cultured mesangial cells and renal epithelial LLC-PK1 and MDCK cells were exposed to RVV (100 to 1000 micrograms/ml) for 5 minutes up to 48 hours. The IPRK dose-dependently exhibited reductions of renal perfusate flow (RPF, 7.7 +/- 2.4 vs. 16.5 +/- 0.7 ml/min g kidney wt in controls, experimental values given are those determined 10 minutes after termination of 100 micrograms/ml RVV admixture), glomerular filtration rate (GFR 141 +/- 23 vs. 626 +/- 72 microliters/min g kidney wt) and absolute reabsorption of sodium (TNa 8 +/- 1.7 vs. 79 +/- 9 mumol/min g kidney wt), and an increased fractional excretion of sodium (FENa 60 +/- 7 vs. 8 +/- 0.8%) and water (FEH2O 68 +/- 3.2 vs. 13 +/- 1.2%). Urinary flow rate (UFR) showed both oliguric and polyuric phases. Functional alterations of this type are consistent with ARF. Light and electron microscopy of perfusion fixed IPRK revealed an extensive destruction of the glomerular filter and lysis of vascular walls. Various degrees of epithelial injury occurred in all tubular segments. In cell culture studies RVV induced a complete disintegration of confluent mesangial cell layers, beginning at concentrations of 200 micrograms/ml. In epithelial LLC-PK1 and MDCK cell cultures only extremely high doses of RVV (> 600 and 800 micrograms/ml, respectively) led to microscopically discernible damage. These results clearly demonstrate a direct dose dependent toxic effect of RVV on the IPRK, directed primarily against glomerular and vascular structures, and on cultured mesangial cells.

The effect of sodium fluoride at prophylactic and toxic doses on renal structure and function in the isolated perfused rat kidney

To assess the renal effects of fluoride, isolated rat kidneys were perfused in single pass mode for 120 min. Five, 15 and 50, as well as 150, 500 and 1500 mumol NaF were administered 60, 80 and 100 min after starting the perfusion, respectively. Kidneys were perfused with constant pressure (100 mmHg). The perfusate consisted of a substrate supplemented Ringer solution containing hydroxy ethyl starch (HES) to produce isoncotic conditions. Concentrations below 500 mumol/l NaF did not induce major changes in the main parameters of renal function. Only upon admixture of the highest concentration of 1500 mumol/l NaF severe changes in renal function could be observed, resulting in complete anuria and a drastic reduction of renal perfusion to 5% of control, associated with a cessation of glomerular filtration. Due to the lack in tubular load, tubular reabsorptive processes inevitably declined to zero. The morphological analysis of kidneys exhibited to 500 mumol/l NaF revealed the occurrence of vesicular material within the urinary space. These vesicles could electron microscopically be identified as membrane enclosed material of podocytic origin. The interstitium was widened. Upon admixture of 1500 mumol/l NaF, kidneys responded with a decrease of the interstitial space. Moreover, epithelial cell swelling, hydropic degeneration of all proximal and distal tubular segments, bleb formation and intraluminal casts were observed frequently. Glomerular capillaries were filled with fine precipitates and their endothelium was severely damaged. The results of our studies in the isolated perfused rat kidney (IPRK) model clearly demonstrate a direct dose dependent acute nephrotoxic effect of NaF only for extremely high doses, which, however, may be reached in human cases of severe fluoride intoxication. On the contrary, for low fluoride doses, especially for those concentrations occurring in human plasma upon cariesprophylactic intake of fluorides, no signs of direct acute nephrotoxic action could be observed in the IPRK model.

Renin stimulating properties of parathyroid hormone-related peptide in the isolated perfused rat kidney

Previous studies showed that PTHrP exhibits renal vasodilating, arteriolar cAMP stimulating and receptor binding properties. The present experiments were designed to study whether PTHrP may influence renin secretion. Rat kidneys were isolated and single-pass perfused at constant flow and stabilized pressure. Exposures to PTHrP or PTH stimulated a dose-dependent renin release reaching similar Vmax. The affinity (0.1 nM) and threshold concentration (0.01 nM) for PTHrP were about 10 times lower than for PTH. Compared to 10 microM isoproterenol, the maximum renin responses to PTHrP were similar but of shorter duration. The PTHrP dose-response curve was not affected by 10 microM indomethacin. Administered simultaneously, PTHrP and PTH displayed no additive effects. PTHrP-induced renin release as well as the role of extracellular calcium were further studied in nonfiltering kidneys, which were perfused at a constant flow and stable pressure in a closed circuit. Basal renin release was inversely related with perfusate calcium and was depressed by the calcium ionophore BAY-K8644. PTHrP (100 nM) induced a 1.6-fold increase of basal renin release in normocalcic perfusate. Removing calcium abolished renin responses. PTHrP reversed the inhibiting effects of hypercalcic media or BAY-K8644 on basal renin release. The results support calcium-mediated renin stimulating properties for PTHrP, via PTH receptors, independently from baroreceptors, macula densa and prostaglandins.

The effects of Escherichia coli heat-stable enterotoxin in renal sodium tubular transport

To compare the function of sodium transport between intestine and renal tubule, we studied the effect of E. coli STa enterotoxin and 8-bromo cyclic GMP in perfused rat kidneys. Infusion of STa enterotoxin (0.017 and 0.1 micrograms/ml) caused a dose and time dependent decrease in total renal sodium tubular transport. The major site of STa effect was at the renal proximal tubule. Similar to Sta enterotoxin, 8-bromo cyclic GMP (10(-5) M) caused a significant decrease of fractional renal sodium proximal tubule transport. In contrast to STa enterotoxin, infusion of 8-bromo cyclic GMP resulted in a significant but short lasting (30 min.) increase in glomerular filtration rate. STa enterotoxin also decreased significantly the renal tissue potassium. This STa effect was related to a significant decrease in renal potassium tubular transport, resulting also in an increase of urinary potassium excretion. These studies demonstrate the specific functional effect of STa enterotoxin in promoting the decrease in renal proximal tubular sodium transport, similar to 8-bromo cyclic GMP. In perfused rat kidneys STa also decreased tissue potassium, mainly by a decrease in potassium transport and increase in urinary potassium excretion. These effects suggest the existence of an endogenous peptide resembling STa enterotoxin, that regulates the function of renal sodium tubular transport.

Basal prostaglandin synthesis by the isolated perfused rat kidney

In order to assess the main characteristics of the prostaglandin (PG) biosynthesis by the isolated perfused rat kidney, the urinary and venous outputs of PGE2, PGF2alpha, 6-keto-PGF1alpha and of thromboxane (Tx)B2 were followed during 120 min after an equilibration period of 30 min. Single pass kidneys were perfused with a Krebs-Henseleit solution added with Polygeline at a constant flow rate providing a perfusion pressure about 90 mm Hg. From the beginning of the study, major differences could be observed in the renal biosynthetic rate of the 4 PG studied which were mainly excreted into the venous effluent. During the perfusion, urinary and venous outputs of PGE2, PGF2alpha and of TxB2 remained stable whereas those of 6-keto-PGF1alpha sharply increased and were found inversely related to the glomerular filtration rate (r = -0.95; p n 0.001). Finally, the urinary and venous outputs of each of the four PGs studied were found positively related. It is concluded that the isolated perfused rat kidney is a valuable preparation for studying the biosynthesis of PGs and that, at least in thi model, the urinary excretion of PGs is a good index of their renal synthesis.

Contribution of amino acids in protective solutions to postischemic functional recovery of canine kidneys

Amino acids are known to increase glomerular filtration rate (GFR). There is also an early resumption of filtration following 2-h renal ischemic stress under protection by histidine-buffered histidine-tryptophan-ketoglutarate solution (HTK), possibly due in part to an amino acid effect. Hence, we have examined the possibility of further enhancing the postischemic GFR by adding 32 (ASP I; 4 mM Mg2+) or 36 (ASP II; 6 mM Mg2+) mM L-aspartate (asp) or 32 mM DL-aspartate (ASP III) to the HTK solution in place of chloride. After infusion of 500 ml 5% glucose, canine kidneys were protected by an 8-min perfusion with HTK (n = 5), ASP I (n = 4), ASP II (n = 5) or ASP III-solution (n = 3). The subsequent ischemia lasted for 2 h at 27-31 degrees C. During reperfusion, both GFR and filtration fraction (FF) were higher in kidneys protected by L-aspartate-containing solutions. ASP III showed no improvement against HTK. An additional preischemic intra-aortal application of HTK or ASP I solution just above the exit of the renal arteries prior to the intrinsic protective perfusion further raised the postischemic GFR. The present results suggest that L-aspartate but also histidine may have favorable amino acid effects in renal protective solutions in addition to known positive effects of histidine.

Aldosterone metabolism in rat renal tissue in vitro. Formation of lipid soluble metabolites

In the present study the formation of lipid soluble metabolites from 3H-aldosterone was investigated in vitro in isolated kidneys and kidney and liver slices of Sprague Dawley rats. The steroids were separated by HPLC (forward and reversed phase systems) and detected on-line as UV- or 3H-chromatograms. Apart from an unenzymatically formed substance, isoaldosterone, three less polar metabolites were traced (A1, A2, A3). The structure of the quantitatively most important metabolite (A1), was identified as 5 alpha-dihydroaldosterone using a combination of techniques such as chromatographic comparison with reference steroids, antibody binding and mass spectrometry. Evidence for further conversion of DHaldo to 3 alpha, 5 alpha-tetrahydroaldosterone was obtained in chromatographic and antibody binding studies. The formation of metabolites was not dependent on glomerular filtration. Furthermore it displayed regional heterogeneity with highest activity in the outer medulla. Finally it was observed that the in vitro metabolism of aldosterone was not saturable over a range of initial aldo concentration of 10(-9) to 10(-5) M.

Renal handling of cadmium and cadmium-metallothionein: studies on the isolated perfused rat kidney

The isolated kidney perfusion model was used to study the uptake of Cd and metallothionein (MT)-complexed Cd. Cd2+ at concentrations above 40 nM strongly depressed the glomerular filtration rate (GFR), whereas MT-complexed Cd (Cd-MT) at concentrations of 0.8-920 nM had no effect on the GFR. In contrast to Cd2+, Cd-MT was readily reabsorbed by the kidney and uptake saturation for Cd-MT occurred at 240 nM. The maximal transport rate for Cd-MT calculated in this study was 18 pmoles Cd-MT . g-1 . min-1. The accumulation of Cd in the kidney was more efficient in the experiment using Cd-MT, in which case the Cd kidney contents were about 2-4 times higher than compared to CdCl2.

Vascular alpha-adrenoceptor blockade by E. coli endotoxin in the rat

It has been previously shown that Escherichia coli endotoxin (ENDO) reduces the pressor effect of phenylephrine. This work attempted to define precisely the involvement of vascular alpha-adrenoceptors in this action. The dose-response curves of three alpha-agonists noradrenaline, St 587 and B-HT 933 in pithed rats were shifted rightwards by pretreatment (i.v. injection of 10 and 100 micrograms/kg) with ENDO. ENDO 10 and 30 micrograms shifted the dose-response curve of noradrenaline in perfused rat kidney. It can be suggested that ENDO has a potent blocking action on vascular alpha-adrenoceptors without evident discrimination between alpha 1 and alpha 2 subtypes.

An inhibitory prejunctional 5-HT1-like receptor in the isolated perfused rat kidney. Apparent distinction from the 5-HT1A, 5-HT1B and 5-HT1C subtypes

The present study has identified a receptor for 5-hydroxytryptamine (5-HT) which functions to inhibit the stimulus-induced release of [3H] noradrenaline following sympathetic periarterial nerve stimulation to the isolated perfused rat kidney. In addition to 5-HT (IC30 = 4.5 X 10(-8) mol/l), both 5-carboxamidotryptamine (IC30 = 8 X 10(-9) mol/l) and 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl) indole (RU-24969, IC30 = 2.5 X 10(-7) mol/l) acted as agonists whereas 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) was inactive. The inhibitory effect of 5-HT on the electrically-evoked release of tritium was antagonized in a concentration-dependent manner by methiothepin (IC50 = 4 X 10(-9) mol/l), metergoline (IC50 = 4 X 10(-8) mol/l) and methysergide (IC50 = 1.3 X 10(-7) mol/l) but not by cyproheptadine, ketanserin, mesulergine, (-)-propranolol, (+/-)-pindolol, (+/-)-cyanopindolol, metoclopramide or phentolamine. It is concluded that the receptor to 5-HT conforms to general criteria defining 5-HT1-like receptors but at the present time the receptor site cannot be fitted to the designated 5-HT1A, 5-HT1B or 5-HT1C subtypes.

Glucose metabolism in renal tubular function

Heterogeneity of metabolic activity along the nephron points to a very varied relationship between glucose metabolism and ion transport. Glycolysis is linked closely to free-water clearance and possibly to sodium, potassium, and hydrogen ion transport. Glucose oxidation, while not the major source of renal energy, is crucial in sodium, potassium, and phosphate reabsorption. Gluconeogenesis recovers carbon compounds generated during the process of renal ammoniagenesis. Glucose synthesis and active sodium transport appear to compete for renal ATP, although no regulatory function for this competition has been identified. Glucose formed in the proximal tubule may support free-water clearance in adjacent distal tubule, but is not thought to contribute to any medullary function. The complex network of biosynthetic and catabolic pathways of glucose metabolism may have evolved in the kidney to protect the organism against wide variations in glucose demand which would otherwise be unavoidable during the course of rapidly fluctuating renal electrolyte loads.

Metabolic control of renal vascular resistance and glomerulotubular balance

Renal vascular resistance (RVR) and glomerulotubular balance were examined in isolated rat kidneys perfused at 100 mm Hg with 10 mM lactate (L) or 10 mM pyruvate (P) or 5 mM glucose (G) either alone or with a mixture of 20 amino acids (13.5 mM, AA); albumin oncotic pressure 24 +/- 1 mm Hg. RVR was L greater than P greater than G = AA. Vasodilation by G and AA was additive. Proximal tubular sodium-cotransport was evaluated from fractional reabsorption (FR) of phosphate (Pi), G, and L. FR Pi was 91% in AA, 86% in P, 72% in L, and 67% in G. Combining AA or P with L or G increased FR Pi to 89 to 90%. FRs of G and L by G and L perfused kidneys were 83 and 78%, respectively, and were increased to 97 to 99% by combining G or L with AA or P. P and AA also increased FR sodium and FR water when combined with L or G or when combined with each other. GFR correlated positively with FR sodium and FR water. AA combined synergistically with L to increase gluconeogenesis. These results indicate that, compared with pyruvate or AA, neither glucose nor lactate alone is a good energy source for proximal tubular reabsorption, that synergistic interactions between AA or pyruvate and lactate or glucose augment GFR by increasing proximal tubular reabsorption, and that the vasodilating effects of glucose and AA are not related directly to their effects on GFR.

Vasoconstrictor and norepinephrine potentiating action of 5-hydroxykynuramine in the isolated perfused rat kidney: involvement of serotonin receptors and alpha 1-adrenoceptors

Kynuramines are endogenously occurring diamines derived from tryptophan. In the present study, we have compared the pharmacological actions of 5-hydroxykynuramine (5-OH-K) with kynuramine and 5-hydroxytryptamine (5-HT) on vascular resistance changes and responsiveness to adrenergic stimuli in the isolated perfused rat kidney. 5-OH-K was found to mimic the actions of 5-HT in that it produced vasoconstriction, potentiation of alpha 1-adrenoceptor-mediated responses to norepinephrine (NE) and periarterial nerve stimulation, and displaced specific [3H]spiroperidol binding from rat cortical membranes. With regard to all parameters measured, 5-OH-K was about 15-times less active than 5-HT. Vascular responses to 5-OH-K and 5-HT were inhibited noncompetitively by ketanserin and cyproheptadine. Unlike 5-OH-K, kynuramine, failed to evoke vasoconstriction and inhibited vascular responses to NE via alpha 1-adrenoceptors. Thus, kynuramine lacks serotonin receptor agonist activity but possesses alpha 1-adrenoceptor blocking properties. In contrast, 5-OH-K potentiates NE and acts as a serotonin agonist. The present results raise the possibility that kynuramine and 5-OH-K might act as endogenous modulators of serotonergic and adrenergic mechanisms in the renal vascular bed.

Corticosteroid metabolism in isolated rat kidney in vitro. I. Formation of lipid soluble metabolites from corticosterone (B) in renal tissue from male rats

Kidneys of male Sprague Dawley rats have been isolated and perfused in vitro in order to study the metabolism of corticosterone (B). B is the main endogenous corticosteroid in this species. Using 3H-B and HPLC for the separation of steroid metabolites it has been possible to detect radioactive derivatives of B which have been denoted as met I, II and III. These substances were purified and compared with authentic reference hormones under different isocratic and gradient elution techniques. We observed chromatographic identity of met I with 11-dehydro-20-dihydro-B, of met II with 20-dihydro-B and of met III with 5 alpha-H-4,5-dihydro-B. From the fact that conversion of B can be observed with normal (50 g X l-1 albumin in perfusate) and elevated (75 g X l-1) colloid osmotic pressure of the recirculating perfusate it can be concluded that B gets access to the metabolic site in renal tissue not solely by glomerular filtration and tubular reabsorption. The metabolites identified presently are excreted in the urine. Metopirone increased the concentration of met I and decreased the concentration of met II. This is compatible with the concept of a stimulatory effect of metopirone on a C-20-hydroxysteroid oxidoreductase and a C-11-hydroxysteroid dehydrogenase.

Corticosteroid metabolism in isolated rat kidney in vitro. III. Structure analysis of lipid soluble metabolites of corticosterone

We have previously demonstrated that isolated rat kidneys in vitro convert corticosterone (B). Four lipid soluble metabolites (met I, II, III and IV) have been identified which differ in polarity from the parent hormone [2, 5, 6, 11, 15, 16]. In the present experiments these metabolites have been extracted from perfusate after 4 h of recirculation through isolated kidneys of male and female rats. Subsequently they have been separated by HPLC using a polar stationary phase system and n-hexane and isopropanol as eluents. The chromatographic comparison of met II with authentic 20 alpha- and 20 beta-isomers documented that met II is identical with 20 beta-dihydro-B. Measurements of the mass spectra of the purified samples revealed the following structures: met I = 20 beta-dihydro-11-dehydro-B, met II = 20 beta-dihydro-B, met III = 5 alpha-H-4,5-dihydro-B and met IV = 11-dehydro-B.

Rabbit kidney function in vitro: the effect of colloids, energy substrate, a vasodilator, perfusion pressure, and bovine serum albumin

An in vitro perfusion system at 37 degrees C for the assessment of rabbit kidney function is described. The purpose of this assay system is to evaluate the effects of cryobiological manipulation on kidney function. The effect of the colloids dextran (MW = 70,000, 80,000, and 180,000) in the perfusate at 110 mm Hg were compared to a reduced perfusion pressure, colloid-free perfusate. Better function was obtained at lower perfusion pressure with the colloid-free perfusate. Less damage was noted histologically on light and electron microscopy. Investigation of energy substrates on rabbit kidney function demonstrated that butyrate, or lactate, in addition to glucose resulted in increased sodium and glucose reabsorption over glucose alone. Substrate-free perfused kidneys exhibited depressed Na transport. Lactate, and to some extent butyrate, decreased net glucose utilization. An alpha-adrenergic blocking agent, isoxsuprine, in the initial flush solution did not appear to be beneficial. An increase of perfusion pressure from 50 to 75 mm Hg resulted in an increase in GFR. Tubular function was enhanced by inclusion of small amounts of BSA in the perfusate.

Activities of enzymes of the tricarboxylic acid cycle in segments of the rat nephron

The activities of enzymes of the tricarboxylic acid cycle were measured in order to compare the respiratory capacity in different parts of the nephron of the rat. Oxoglutarate dehydrogenase, citrate synthase and isocitrate dehydrogenase were assayed in single nephron segments dissected out of freeze-dried cryostat sections. The activities of the three enzymes per unit weight are higher in the distal segments (thick ascending limb and distal convoluted tubule) than in the proximal tubule. The distal vs. proximal ratios of activities are about 1.5, 2.5 and 2 for oxoglutarate dehydrogenase, citrate synthase and isocitrate dehydrogenase, respectively. Oxoglutarate dehydrogenase shows the lowest activities along the whole nephron and appears to catalyze the rate-limiting step of the tricarboxylic acid cycle. The possibility to estimate the respiratory capacity in the different segments of the nephron on the basis of the activity of oxoglutarate dehydrogenase is discussed. The capacity calculated for the proximal tubule (between 44 and 66 mumol O X min-1 X g-1, depending on the substrate) is in agreement with direct measurements of oxygen consumption as well as with calculations made on the basis of morphometrical data.

Renal metabolism of corticosteroid hormones

IK and STF from male and female rats have been used to study in vitro the renal metabolism of B. in male rat tissue four lipid soluble metabolites (I-IV) have been found, I + II being more polar and III + IV being less polar than B. I and II have been identified as 11-dehydro-20-hydroxy-B and 20-hydroxy-B. The structure of III and IV remains to be determined. Renal tissue from female rats produced predominantly III indicating sexual variations of steroid metabolism in kidneys.--The literature has been reviewed which documents that the kidneys in addition to B metabolize A, cortisol, progesterone and other corticosteroids.

Renal handling of homologous and heterologous insulin in the isolated perfused rat kidney

1. Renal handling of pig- and rat-insulin was studied in the isolated perfused rat kidney. 2. Metabolic clearance rates of both pig- and rat-insulin exceeded GFR. 3. Peritubular uptake of pig-insulin accounted for 13% of rat-insulin for 31% of the total metabolic clearance. 4. The nonfiltering kidney does not remove insulin from the peritubular circulation. 5. Metabolic clearance rates of pig- and rat-insulin are directly related to GFR. 6. The filtration process seems to be necessary for the uptake of insulin at the peritubular site.

Presynaptic inhibition of sympathetic neurotransmission by adenosine in the rat kidney

The effect of adenosine on responses to sympathetic nerve stimulation was studied in the isolated perfused rat kidney. Adenosine at 1, 3 and 10 micrograms/ml caused significant impairment of renal sympathetic neurotransmission as evidenced in a dose-dependent reduction in the vasoconstrictor responses elicited by periarterial nerve stimulation at 2, 4 and 8 Hz. Vasoconstriction to exogenous norepinephrine was unaffected by adenosine except at 10 micrograms/ml where there was a slight reduction in response to norepinephrine. Theophylline, an adenosine receptor antagonist, inhibited the above action of adenosine at the frequencies of 2 and 4 Hz. At 2 Hz, 10 microM theophylline completely blocked the effect of 1 and 3 micrograms/ml adenosine and reduced by 50% the inhibitory action of 10 micrograms/ml. Higher concentration of theophylline (50 microM) was required to antagonize the action of adenosine at 4 Hz. These results indicate that adenosine can inhibit sympathetic neurotransmission in the rat kidney through a presynaptic purinergic mechanism. The physiological and pharmacological significance of this presynaptic action of adenosine is discussed.

Organic substrate effects on and heterogeneity of Necturus proximal tubule function

The effect of organic substrates such as lactate, alanine, glutamine, glutamate, lysine, and butyrate is compared with that of glucose, and the role of tubular heterogeneity is assessed in Necturus proximal tubule. Fluid absorption (Jv) is enhanced 34% by the presence of all substrates together in the tubular lumen. Addition of glucose to the peritubular perfusion fluid does not increase Jv significantly, whereas the other substrates augment Jv by 181%. Transepithelial potential difference (V3) and peritubular membrane potential difference (V1) are unaffected by these organic substrates. Transepithelial chloride to sodium transference number ratios (tCl/tNa) and transepithelial specific resistance (Rm) are higher in the presence of substrates, possibly because of effects on paracellular conductance. Organic solutes could influence fluid absorption by increasing entry of sodium across the luminal cell membrane, by increasing energy supply to the active transport mechanism, or by decreasing paracellular conductance. Early and late straight segments of the proximal tubule do not differ significantly in V3, V1, and transepithelial tCl/tNa. Early convoluted segments have a higher Jv than do late straight proximal segments, but they have a lower transepithelial specific resistance. We have concluded that net fluid absorption and transepithelial ionic conductance correlates with the supply of certain organic solutes and with specific localization along the proximal tubule.

Glomerular albumin filtration: a comparison of micropuncture studies in the isolated perfused rat kidney with in vivo experimental conditions

Glomerular albumin filtration was investigated in the isolated perfused rat kidney and compared with in vivo experiments. Applying micropuncture techniques, we obtained samples from the glomerulus or adjacent early proximal convoluted tubules (EPT) of cortical nephrons and analyzed them for albumin using ultramicrodisc electrophoresis. By determining albumin in glomerular filtrate, we could calculate the sieving coefficient (EPTalb/Palb) directly. The control in vivo value was 0.27 +/- 0.05 X 10(-3) (N = 11). In the isolated perfused rat kidney, the sieving coefficient was 2.1 +/- 0.8 X 10(-3), N = 18 (30 g/liter albumin in perfusate) and 2.3 +/- 0.8 X 10(-3), N = 13 (50 g/liter albumin in perfusate), which is approximately eight times the control in vivo value. With elevated renal venous pressure (20 cm H2O), it increased further to 5.4 +/- 1.6 X 10(-3), N = 8. In all experiments, GFR and proximal transit times were similar to the in vivo controls. Although no major morphologic changes could be detected in any instance, the albumin filtration was greatly elevated. These data confirm the role of a functional barrier in the prevention of glomerular albumin filtration.

Effects of vasopressin and its deamino-D-arginine analogue on renin release in the isolated perfused rat kidney

The direct action of arginine-vasopressin (AVP) and its deamino-D-arginine analogue (DDAVP) on renin release (RR) has been studied in isolated rat kidneys perfused with an electrolyte solution at constant pressure in a single-pass system. AVP and DDAVP infused at various concentrations (80 to 2100 pg/ml and 80 to 8700 pg/ml, respectively) reduced volume and increased osmolality of urine in a dose-dependent way. High doses of AVP reduced renal perfusate flow and glomerular filtration rate while DDAVP had no effect on renal haemodynamics. When vasoconstrictor doses of AVP or high concentrations of DDAVP were infused, "basal" RR remained unchanged. However, when RR had been stimulated by infusion of isoproterenol, vasoconstrictor doses of AVP as well as high doses of DDAVP which did not increase renal vascular resistance diminished RR by about 30% (P less than 0.01, and P less than 0.05, respectively). These results suggest that the inhibition of RR by vasopressin is not related to its vasoconstrictor action.

Volume changes in cells of the outer medulla during perfusion of the rat kidney

1. A method is described for the perfusion of the rat kidney with a medium resembling rat plasma in its ionic constituents but with 3% polyvinylpyrrolidone (mol.wt. 44,000) replacing the plasma proteins. 2. In the early stages of perfusion, there was rapid swelling of the tubular cells in the outer medulla, a low glomerular filtration rate and a low filtration fraction. 3. After 30 min perfusion, the tubular cell volume in the outer medulla was normal and filtration had increased and stabilised. 4. Cell swelling and the low initial filtration fraction were prevented by (a) adding 50 mM-mannitol to the basic medium, (b) replacing 50 mM-NaCl with 50 mM-choline chloride, or (c) adding 5% human serum to the basic medium. 5. The addition of human serum to the perfusion medium depressed the fractional reabsorption of sodium and potassium; sodium from 0.94 +/- 0.01 (S.E. of mean) with the basic medium to 0.79 +/- 0.02 with basic medium +5% serum after 35 min perfusion; and potassium from 0.73 +/- 0.04 with the basic medium to 0.37 +/- 0.05 with the basic medium +5% serum after 35 min perfusion. 6. Two conclusions are drawn from the observations: first, that at the start of perfusion the effective internal osmolality of tubular cells of the outer medulla is greater than that of cortical cells and of the basic medium; and second, that the presence of small amounts of plasma proteins in the perfusion medium has a marked effect on the properties of plasma cell membranes.

Role of cyclic AMP in the regulation of renin release from the isolated perfused rat kidney

The role of cyclic AMP in the regulation of renin release (RR) was studied in isolated rat kidneys, which were perfused at constant pressure in a single-pass system with a modified Krebs-henseleit solution. Isoproterenol (IP) (2 x 10(-9) to 2 x 10(-6) M) and 3-isobutyl-1-methyl-xanthine (IBMX) (4 x 10(-7) to 7 x 10(-5) M) induced a dose-dependent increase of renal perfusate flow, glomerular filtration rate and urinary sodium excretion. RR was stimulated up to 10-fold above control values within 5 min. At the lowest concentrations IP stimulated RR, but did not affect renal haemodynamics. When IP and IBMX were administered concomitantly, a supraadditive stimulation of RR was observed. Dibutyryl-cAMP (db-cAMP) and 8-Br-cGMP (10(-6) to 10(-4) M) produced a similar dose-dependent vasodilation and natriuresis, but differed in their action on RR. Within 15 min after the start of the infusion, db-cAMP increased RR up to 4-fold, whereas 8-Br-cGMP was without an effect. These results suggest that IP, IBMX and db-cAMP stimulated RR by increasing the concentrations of cAMP in the epitheloid cells and independently of changes in renal haemodynamics and sodium excretion.

Substrate-limited function and metabolism of the isolated perfused rat kidney: effects of lactate and glucose

1. The objective of this study was to determine the separate contributions of exogenous substrate and of kidney tissue to the support of function and metabolism in the isolated perfused rat kidney. The effects of the addition of L(+) [U-14C]lactate or D[U-14C]glucose either to a specially prepared substrate-free albumin (SFA) or to Fr. V bovine serum albumin (Fr. V-BSA) were compared. The Fr. V-BSA has significant quantities of lactate, citrate and free fatty acids associated with it. 2. Perfusion of the rat kidney with the Krebs-Ringer bicarbonate solution containing SFA, without addition of exogenous substrate, resulted in a lower % Na+ reabsorption (approximately 43%) than when the perfusions contained Fr. V-BSA (approximately 80%). Thus, kidney tissue can support at most 45% of Na+ reabsorption, while the substrates associated with the Fr. V-BSA can support approximately 30% of Na+ reabsorption. When the initial concentration of L(+)lactate in the perfusate containing SFA was progressively raised from 0 to 10 mM, % Na+ reabsorption increased to between 85 and 90%. 3. The apparent Km (0-59 mM) and the Vmax (0-67 micronmole g-1. min-1) for lactate oxidation in the presence of SFA were both significantly lower than when Fr. V-BSA was present (Km = 2-0 mM; Vmax = 1-1 micronmole g-1. min-1). The lower Km is interpreted as being due to the removal of substances from the Fr. V-BSA which competitively inhibit either the uptake or oxidation of lactate; the lower Vmax is considered to be related to the lower rate of Na+ reabsorption when SFA is present. 4. Addition of glucose enhanced gomerular filtration rate in the presence of both types of albumin. The resulting increase in the filtered load of Na+ in the presence of glucose was associated with either no change (Fr. V-BSA) or an increase (SFA) in fractional Na+ reabsorption. Although absolute Na+ reabsorptive rate was greater in the presence of glucose than in the presence of lactate, the oxidation rate of glucose, on a carbon-atom basis, was less than 50% of the oxidation rate of lactate. 5. The metabolism of glucose may regulate the permeability characteristics of the glomerulus and the tubular epithelium: by contrast, the high oxidation rate of lactate suggests it can provide direct support for a major fraction of the Na+ actively absorbed.