Stimulation of renal tubular transport by ethacrynic acid in rats of different ages.

The transport system for organic acids in the kidney is not fully developed in the neonatal period. The effect of repeated administrations of ethacrynic acid on the renal excretion of p-aminohippurate (PAH) was studied in rats of different ages. Pretreatment with ethacrynic acid was followed by an increase in the renal excretion of PAH in 33-, 55-, 105- and 240-day-old rats but not in newborn rats. In 55-day-old rats the increase in renal excretion of PAH after pretreatment with ethacrynic acid was not associated with any consistent change of the glomerular filtration rate. It is concluded from these results that the stimulation of transport processes in the kidney by ethacrynic acid and some other drugs is linked with their affinity to tissue proteins.     

Acceleration of p-aminohippurate excretion in immature rats by dexamethasone treatment

In 5-, 10- and 15-day-old rats repeated administration of dexamethasone caused a dose-dependent increase of p-aminohippurate (PAH) excretion. Remarkably, dexamethasone has no influence on PAH excretion in adult rats. The effect of treatment in young rats cannot be explained by an increase in the glomerular filtration rate. In 10-day-old rats GFR shows a tendency to increase. In renal cortical slices from 5-day-old rats PAH transport is increased following dexamethasone treatment, whereas in 10- and 15-day-old rats an increase of kidney mass seems to be responsible for acceleration of renal excretion of PAH after administration of dexamethasone. In 5-day-old rats only the protein content is statistically significantly increased after dexamethasone treatment.     

Extent and duration of drug-induced stimulation of renal excretion of p-aminohippuric acid]

Repeated pretreatment with p-aminohippuric acid (PAH), probenecide, cyclopenthiazide, and phenobarbital stimulates the renal excretion of PAH. For an interval of at least 6 hrs following i.p. application pretreated rats excrete more PAH excretion than the controls. All the drugs studied were found to stimulate renal PAH excretion within a period of 3 hrs by 50-60% of the control value. The required duration of pretreatment varies with the substance used. With cyclopenthiazide, the excretion of PAH is demonstrable for 2-3 weeks. Phenobarbital has a brief stimulating action. Correlations of a binding of drugs to structures of their tubular cell and the length of the stimulating action are discussed.     

Stimulation of the renal excretion of p-aminohippuric acid by repeated application of phenobarbital]

The rate of renal excretion of p-aminohippuric acid can be accelerated by repeated administration of phenobarbital in adult rats. This stimulation could not be observed in newborn and young rats.     

Influence of neomycin pretreatment on stimulated and maturative renal transport of p-aminohippurate (PAH)

Renal tubular transport of organic anions is immature at birth and can be stimulated in adult rats by repeated administration of xenobiotics. There is some evidence of an increased synthesis of carrier proteins in renal tubular cells following stimulation as well as during postnatal development of renal tubular transport processes. The effect of pretreatment with an inhibitor of protein biosynthesis (neomycin) on stimulated and maturative transport of p-aminohippurate (PAH) was measured. Neomycin has a dose dependent long acting and reversible effect on stimulated PAH transport and on postnatal maturation of PAH excretion, and increased protein biosynthesis is the likely common basic phenomenon of both processes.     

Hormonal regulation of postnatal development of renal tubular transport processes

Renal tubular transport of p-aminohippurate (PAH) is immature at birth. Repeated saturation of transport sites by treatment with various organic anions is without any influence on the postnatal development of kidney transport capacity. Hormonal regulation of postnatal maturation of PAH transport must therefore be taken into consideration. It was tried to stimulate immature PAH transport by treating rats of different ages with thyroid hormones, corticosteroids or testosterone, respectively. In rats with immature kidney function, renal PAH excretion can be stimulated by daily treatment with thyroid hormones. Experiments on renal cortical slices have shown that PAH excretion is preferentially stimulated by an increase of transport capacity. Whereas thyroid hormones stimulate the renal excretion of PAH both in young and in adult rats, dexamethasone treatment is more effective in rats with immature kidney function. Dexamethasone treatment is without any influence on PAH accumulation in renal cortical slices. Kidney weight and the protein content of kidney tissue was increased after dexamethasone treatment. Repeated testosterone administration did not stimulate the PAH transport in rats of different ages. The data have demonstrated the influence of thyroid hormones or of dexamethasone on renal tubular transport processes in rats with immature kidney function. Treatment with such hormones could be useful in the management of renal insufficiency in full-term and pre-term neonates with immature kidney function.     

Inhibition of kidney function after blockade of thromboxane synthetase by imidazole in anaesthetized rats

Experiments on anaesthetized female Wistar rats have shown that imidazole reduces renal excretion of p-aminohippurate (PAH). This effect occurs only after administration of imidazole simultaneously with a volume load (2 ml/100 g b.wt.). Injection of imidazole immediately before a PAH bolus (100 mg/100 g b.wt. in 2 ml) is followed by reduced PAH excretion via urine for at least 1 hour. In contrast, if a PAH bolus is given 20 min or later after imidazole no effect of this drug on renal PAH transport is demonstrable. These findings indicate that imidazole can interfere effectively with thromboxane synthesis only if thromboxane production is activated by volume expansion. Interestingly, despite 40% reduction of renal PAH excretion in volumen loaded rats, PAH serum disappearance is identical in controls and imidazole treated rats. Thus differences in the volume of distribution for PAH after imidazole must be expected. Under our experimental conditions imidazole was without effect on renal electrolyte excretion.     

Comparison of the effects on inhibition of cyclooxygenase and thromboxane synthetase on renal excretion and haemodynamics in rats of different ages

Effects of the cyclooxygenase inhibitors indomethacin, naproxen and the thromboxane synthetase inhibitor imidazole on renal sodium water and p-aminohippurate excretion were investigated in sodium loaded conscious rats of different ages. Renal and intrarenal blood flow were studied in anaesthetized adult rats. Indomethacin and naproxen reduced PAH excretion in 5- and 10-day-old rats but not in rats of older ages. Imidazole failed to influence PAH-excretion in young animals. The excretion of PAH was decreased in adult rats at 10 and 60 min following imidazole administration, but not after longer time interval (120 min). Following indomethacin and naproxen administration urine output was decreased in 5-, 10- and 15-day-old rats, but not in rats of older ages. Effects of imidazole on electrolyte excretion can be demonstrated in adult rats only. Cardiac output was not altered by the three drugs. Blood pressure was elevated after indomethacin, but remained unchanged after naproxen and imidazole treatment. Renal and cortical blood flow remained unaltered and no redistribution was seen in intrarenal blood flow after indomethacin, naproxen and imidazole administration. The experimental data suggest that prostaglandins and thromboxanes are involved in the regulation of kidney function, but prostaglandins in the rat--in contrast to the dog--do not seem to play a major role in the regulation of renal vascular tone in adult animals.     

Succinate dehydrogenase activity in rat kidney after repeated administrations of p-aminohippurate or sodium chloride

During PAH excretion and 18 h after repeated PAH administrations to rats, renal cortical SDH activity was unchanged in comparison with untreated controls. On the other hand, 18 h after repeated administrations of 0.9% or 1.8% NaCl solution, SDH activity was decreased by about 20% in kidney cortex. In outer medulla SDH activity was decreased 18 h after all pretreatments. The decline of SDH activity was observed whenever an increased urinary Na excretion occurred, except that PAH was repeatedly administered. The probability is discussed that substrate-induced stimulation of the carrier system for weak organic acids is accompanied by an increase of mitochondrial activity in kidney cortex.     

The Effects of Diuretics on Renal Clearances in Pigs

The following diuretics have been examined for their influence on renal clearances in pigs: chlorthiazidum (2 mg/kg), hydrochlor-thiazidum (0.2 and 2 mg/kg), furosemidum (0.5 mg/kg) and mer- salylum (2.5 and 10 mg/kg). The investigation comprised determinationof the clearances of inulin, endogenous creatinine, urea, PAH, sodium, potassium and chloride, before and after the administration of the diuretics. Ghlorthiazidum, hydrochlorthiazidum and mersalylum in the low dose did not affect the clearances of inulin, endogenous creatinine, urea and PAH. When furosemidum was administered, there was first a slight increase and then a decrease in those clearances. After administration of 10 mg/kg mersalylum, there was a strong decrease in the inulin, endogenous creatinine, urea and PAH clearances, and simultaneously glucose and protein could be found in the urine. All four diuretics caused a markedly increased excretion of sodium and chloride, while the excretion of potassium was only moderately increased. The effect on the excretion of sodium and chloride was of about the same order of magnitude for chlorthiazidum and hydrochlorthiazidum, though the effect of the latter was slightly more prolonged. In contrast to those two diuretics, furosemidum had a very strong but short effect. The influence of mersalylum on the excretion of sodium and chloride was somewhat stronger and more prolonged than that of the thiazides. Histological examinations of the kidneys of the pigs given 10 mg/kg mersalylum revealed pronounced tubular degeneration, particularly in the proximal tubules.     

Organic anion transporters involved in the excretion of bestatin in the kidney

Bestatin, a dipeptide, a low molecular weight aminopeptidase inhibitor, has been demonstrated to be an immunomodulator with an antitumor activity. However, the transporter-mediated renal excretion of bestatin is not fully understood. The purpose of this study was to elucidate the transporter-mediated renal excretion mechanism for bestatin. The plasma concentration of bestatin was increased markedly and both the accumulative renal excretion and renal clearance of bestatin were decreased significantly after intravenous administration of bestatin in combination with probenecid. p-Aminohippuric acid (PAH), a substrate of organic anion transporter (OAT) 1, benzylpenicillin (PCG), a substrate of OAT3 and JBP485, a substrate of OAT1 and OAT3, reduced the uptake of bestatin in rat kidney slices and in hOAT1- or hOAT3-HEK 293 cells. The accumulation of bestatin in hOAT1-HEK and hOAT3-HEK 293 cells was significantly greater than that in vector-HEK, and the K(m) and V(max) were 0.679 ± 0.007 mM and 0.807 ± 0.006 nmol/mg protein/30s for OAT1, 0.632 ± 0.014 mM and 1.303 ± 0.015 nmol/mg protein/30s for OAT3 respectively. PAH and JBP485 inhibited significantly the uptake of bestatin in hOAT1-HEK with the K(i) values of 92 ± 9 μM and 197 ± 21 μM; and PCG, JBP485 inhibited significantly the uptake of bestatin in hOAT3-HEK 293 cells with the K(i) values of 88 ± 12 μM and 160 ± 16 μM. Our results are novel in demonstrating for the first time that OAT1 and OAT3 are involved in the renal excretion of bestatin.     

Compensation of renal drug excretion after unilateral nephrectomy

Twenty hours after unilateral nephrectomy (uNX) the PAH excretion of uninephrectomized rats reaches about 80% of the controls. Immediately after removal of one kidney the parenchyma loss can be compensated by an intensification of glomerular filtration. Thereafter the active tubular secretion capacity raises. 24 h after uNX, a significant increase of renal mass could be measured. The specific PAH accumulation capacity per 1 g renal cortical tissue increases significantly 96 h after uNX if the animals had been pretreated with cyclopenthiazide before the operation. Administration of azauracil or fluoruracil or neomycin causes a dose-dependent reduction of PAH elimination in sham operated as well as in uNX-rats. The effect of stimulation by cyclopenthiazide, also occurring after uNX could be reduced significantly by the inhibitors. The relative extent of compensation (80 +/- 10%) was not influenced by the inhibitors of protein synthesis. The compensation after uNX and the stimulation of renal tubular function are mediated by different mechanisms.     

Compared effects of isoxicam and indomethacin on the urinary excretion of prostaglandins in degenerative articular diseases

The effects of a 7 day-treatment with isoxicam (200 mg/24 h) on the urinary excretion of prostaglandins (PG) were compared to those of indomethacin (150 mg/24 h) in a double-blind randomized study conducted in 18 patients with degenerative arthritic disease and normal renal function. Indomethacin decreased the urinary excretion of PGF2 alpha by about 70% and 6-keto-PGF1 alpha and thromboxane (Tx)B2, the stable break-down products of prostacyclin and TxA2 respectively, by about 40%. Isoxicam effects on urinary PG did not significantly differ from those of indomethacin. During both treatments, urinary gamma-glutamyl transferase and N- acetyl-glucosaminidase remained stable and none of the changes in the urinary excretion of PGs could be related to either plasma or urinary drug concentrations. In conclusion, chronic administration of isoxicam inhibited the renal PG biosynthesis to a similar extent than indomethacin which suggests that non steroidal anti-inflammatory drugs of the oxicam group ought also be used cautiously in patients with renal impairment.     

Evidence for a secretory component in the handling of unconjugated bilirubin by the isolated perfused rat kidney

Previous studies in rats have suggested that the urinary excretion of unconjugated bilirubin (UB) comprises only a small fraction of the pigment that reaches the tubular lumen by glomerular filtration and escapes from tubular cell reabsorption. However, additional data also indicated that UB interacts with renal peritubular cell membranes impairing the secretion of p-aminohippurate (PAH). In this study we examined the possibility of a secretory step which could also be involved in the renal excretory mechanism for UB. An isolated rat kidney preparation was used, and the uptake of UB by renal tissue, the UB appearance in the urine, and the secretion of PAH were analyzed throughout the perfusion. The results indicated that the UB urinary excretion rate changed independently of UB filtered load. The latter remained almost unchanged during the perfusion, whereas the excretion rate of UB and the UB-to-creatinine (Cr) clearance ratio increased significantly. Furthermore, a relationship between the uptake of UB by the kidney, the UB-to-Cr clearance ratio, and the decrease in PAH secretion rate, was proved. In addition, when probenecid was added to the perfusate solution the cumulative uptake of UB by the kidney and the rate of excretion of UB in the urine were diminished. We conclude that the mechanism of UB excretion by the kidney may be considered as the result of a process involving glomerular filtration plus tubular secretion followed by a back diffusion step from the lumen in a similar way to other endogenous compounds, thus explaining the virtual absence of UB from the normal urine.     

Accumulation of p-aminohippuric acid and cyclopenthiazide in renal cortex slices from rats of various ages and their dependence on the energy supply]

The accumulation of p-aminohippuric acid (PAH) and cyclopenthiazide, two drugs of acidic character and extremely different physico-chemical properties, was determined in renal cortical slices of rats aged 5, 15, 33, 55, 105, and 240 days. PAH is accumulated in the cortical slices of 5- and 15-day-old animals to a lesser extent than in those of adult rats. Cyclopenthiazide is accumulated in much higher amounts than PAH in all age groups. The age dependence of cyclopenthiazide accumulation is not so pronounced as with PAH accumulation. There is no accumulation of PAH in the cortical slices of all age groups through active tubular transport, when the energy supply is inhibited by means of 2,4-dinitrophenol (DNP) or nitrogen 2 times bubbling (i.e. anaerobic incubation). By subsequent addition of DNP to the incubation medium or subsequent N2 atmosphere bubbling, an already existing PAH accumulation may be completely nullified. Contrary to PAH accumulation, cyclopenthiazide accumulation can be neither prevented nor abolished by inhibiting the energy supply.     

Protection of glomerular filtration rate by the thromboxane receptor antagonist L655,240 during low dose cyclosporine administration

Cyclosporin A (CsA) alters the production of prostaglandins (PG) by the kidney. CsA causes an increase in renal vascular resistance, a decrease in renal blood flow, a decrease in glomerular filtration rate (GFR), and increases the renal production of the vasoconstrictor thromboxane. Recently, low dose CsA has been utilized in the treatment of refractory autoimmune diseases. To determine if low dose CsA administration could produce renal hemodynamic alterations and to determine if the thromboxane receptor antagonist L655,240 could prevent these alterations, we administered groups of rats either CsA, 5 mg/kg, subcutaneously and the L655,240 vehicle NaHCO₃ (CsA-NaHCO₃), or CsA and L655,240 (CsA-L655,240), or CsA vehicle and L655,240. The rats were administered the drugs for 7 days and then subjected to inulin and PAH clearances or kidneys were harvested for prostaglandin production studies. CsA significantly depressed GFR and renal plasma flow when compared to the L655,240 treated groups. There was no difference in inulin or PAH clearance between the CsA-L655,240 and CsA vehicle L655,240 groups. Glomerular prostaglandin production including thromboxane was depressed by CsA administration. No histologic alterations were noted in the glomeruli or the medullary portions of the kidney. We conclude that administration of low dose CsA, 5 mg/kg, for 7 days results in a decrease in renal blood flow and GFR without histologic alterations. Administration of the thromboxane receptor antagonist L655,240 prevents the renal hemodynamic alterations induced by CsA in this rat model.     

Stimulation of renal phosphate secretion in the stenohaline freshwater teleost: Carassius auratus gibelio Bloch

1. Renal excretion of phosphate in the Prussian carp was modulated by tubular reabsorption and tubular secretion. 2. Under the conditions of an i.v. phosphate-load during which the plasma concentration of phosphate was doubled, 65% of the phosphate load was excreted by the kidney, mainly by tubular secretion. 3. The renal clearance of PAH markedly exceeded the clearance of polyfructosan which could be used for the measurement of the GFR. 4. A transport maximum for tubular PAH secretion was reached at plasma concentrations of about 250 mumol/l.     

Gentamicin nephrotoxicity. II. Physiological, biochemical and morphological effects of prolonged administration to rats.

The purpose of this investigation was to determine the morphological, physiological and biochemical effects of gentamicin upon the rat kidney following prolonged administration of the antibiotic. Sprague-Dawley and Fischer 344 strain rats were given 3, 10, 20 or 40 mg gentamicin per kg body weight per day for 28 days. Morphologic alterations were evaluated by light and electron microscopy. Functional parameters included glomerular filtration rate, PAH secretion, renal plasma flow, sodium reabsorption, potassium excretion, urine volume and protein, and serum urea nitrogen. Oxidative metabolism of mitochondrial fractions from renal cortical homogenates was evaluated by oxygen uptake and P:O ratios. The results indicate focal proximal tubular injury, decreased tubular maximum secretion of PAH, and altered oxidative metabolism at the higher dose levels of gentamicin. Neither elevations of serum urea nitrogen nor alterations in glomerular filtration rate, renal plasma flow, or sodium or potassium excretion were observed. Thus, it appears that high dose levels (40 mg per kg per day) alter the structure and function of some proximal tubular segments when administered over prolonged periods. The alterations appear reversible. Although nephro-toxicity is identified under these conditions in rats, extrapolation to human patients usually receiving much lower doses must be guarded.     

Protection of glomerular filtration rate by the thromboxane receptor antagonist L655,240 during low dose cyclosporine administration.

Cyclosporin A (CsA) alters the production of prostaglandins (PG) by the kidney. CsA causes an increase in renal vascular resistance, a decrease in renal blood flow, a decrease in glomerular filtration rate (GFR), and increases the renal production of the vasoconstrictor thromboxane. Recently, low dose CsA has been utilized in the treatment of refractory autoimmune diseases. To determine if low dose CsA administration could produce renal hemodynamic alterations and to determine if the thromboxane receptor antagonist L655,240 could prevent these alterations, we administered groups of rats either CsA, 5 mg/kg, subcutaneously and the L655,240 vehicle NaHCO3 (CsA-NaHCO3), or CsA and L655,240 (CsA-L655,240), or CsA vehicle and L655,240. The rats were administered the drugs for 7 days and then subjected to inulin and PAH clearances or kidneys were harvested for prostaglandin production studies. CsA significantly depressed GFR and renal plasma flow when compared to the L655,240 treated groups. There was no difference in inulin or PAH clearance between the CsA-L655,240 and CsA vehicle L655,240 groups. Glomerular prostaglandin production including thromboxane was depressed by CsA administration. No histologic alterations were noted in the glomeruli or the medullary portions of the kidney. We conclude that administration of low dose CsA, 5 mg/kg, for 7 days results in a decrease in renal blood flow and GFR without histologic alterations. Administration of the thromboxane receptor antagonist L655,240 prevents the renal hemodynamic alterations induced by CsA in this rat model.     

Epidermal growth factor (EGF) increases the renal amino acid transport capacity in amino acid loaded rats

Summary In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal amino acid handling was investigated in glutamine, arginine (both 50 mg/100 g b. wt. per hour), or alanine (90 mg/ 100 g b. wt. per hour) loaded animals. Continuous infusions of the three amino acids were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment (8g/100g b. wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was followed by a stimulation of renal amino acid reabsorption. The increase in the fractional excretion of the administered amino acids was significantly lower than in non-EGF-treated rats. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pretreatment (0.96 ± 0.10 vs. 0.62 ± 0.07 ml/min X 100 g b. wt.) and a distinct increase in sodium excretion (2.98 ± 0.55 vs. 4.97 ± 0.71val/100 g b. wt. X 20 min). After loading with p-aminohippurate (PAH; 200mg/100g b. wt.), PAH excretion in EGF rats was increased by about 20%, whereas urinary protein excretion was lower in EGF pretreated rats (control: 0.45 ± 0.04 vs. EGF: 0.18 ± 0.03 mg/ 100 g b. wt. X 20 min). The PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions. Furthermore, EGF pretreatment depressed normal kidney weight gain significantly (874 ± 18 vs. 775 ± 32mg/100g b. wt.). EGF can improve the renal tubular transport capacity, but, compared to well-known stimulators of renal transport like dexamethasone or tri-iodothyronine, its effect is only of a moderate degree.