Renal Excretion Of P-aminohippurate Research Articles

Postnatal development of kidney function in rats receiving thyroid hormones.

In immature rats, renal excretion of p-aminohippurate (PAH) can be increased by daily pretreatment with triiodothyronine (T3) or tetraiodothyronine (T4) beginning on the 2nd day after birth (10 micrograms/100 g b.wt. i.p.). The increase of PAH excretion is nearly of the same extent, if 5-, 10-, 20-, 30-, 50-, and 105-day-old rats were pretreated with thyroid hormones (10 micrograms/100 g b.wt. i.p., 3 days, once daily). There is no strongly dose dependent renal effect of T3 and T4, respectively. The time course of stimulation of renal PAH excretion was also characterized in rats of different ages. Simultaneous pretreatment of young and adult rats with cyclopenthiazide and T3 is not distinctly more effective as both components given alone. Particularly the low degree of stimulation in young rats receiving cyclopenthiazide cannot be pronounced by additional T3 administration. Inhibitors of protein biosynthesis (azauracil, neomycin) can antagonize the stimulation of renal p-amino-hippurate excretion in rats receiving T3. The presented data indicate that T3 is effective in young rats. Furthermore, T4 can be converted to T3 in young rats, too. The importance of an intact protein synthesis seems to be a prerequisite to stimulate the kidney function by T3 pretreatment.

Altered expression of rat renal cortical OAT1 and OAT3 in response to bilateral ureteral obstruction

Bilateral ureteral obstruction (BUO) is characterized by the development of hemodynamic and tubular lesions. However, little is known about the expression of organic anion renal transporters. The objective of this work was to study the renal excretion of p-aminohippurate (PAH) and the cortical renal expression of the organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) in BUO rats. Male Wistar rats underwent bilateral obstruction of the proximal ureters for 24 hours (BUO) or sham operation. After 24 hours of ureteral releasing, the following studies were performed: PAH renal excretion employing conventional clearance techniques and OAT1 and OAT3 abundance (homogenates, intracellular and basolateral plasma membrane fractions from renal cortex) using immunoblotting and immunocytochemical techniques (light microscopic and confocal immunofluorescence microscopic analysis). BUO rats showed a lower renal excretion of PAH. In obstructed kidneys, immunoblotting revealed a significant decrease in the abundance of both OAT1 and OAT3 in basolateral plasma membranes from renal cortex. An increase of OAT1 expression was observed in homogenates and in intracellular membrane fractions in kidneys from BUO rats compared with sham-operated ones, indicating an internalization of this carrier. Immunocytochemical techniques confirmed these results. On the contrary, OAT3 expression was reduced both in homogenates and in intracellular membrane fractions in obstructed kidneys. BUO was associated with down-regulation of OAT1 and OAT3 in basolateral plasma membranes from proximal tubule cells, thus these carriers may play important roles in the impaired organic anion excretion displayed in the obstructed kidney.

Altered renal elimination of organic anions in rats with chronic renal failure

The progress of chronic renal failure (CRF) is characterized by the development of glomerular and tubular lesions. However, little is known about the expression of organic anions renal transporters. The objective of this work was to study, in rats with experimental CRF (5/6 nephrectomy), the expression of the organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) and their contribution to the pharmacokinetics and renal excretion of p-aminohippurate (PAH). Two groups of animals were used: Sham and CRF. Six months after surgery, systolic blood pressure and plasma creatinine concentrations were significantly higher in CRF groups. CRF rats showed a diminution in: the filtered, secreted and excreted load of PAH; the systemic clearance of PAH; the renal OAT1 expression; and the renal Na-K-ATPase activity. No remarkable modifications were observed in the OAT3 expression from CRF kidneys. The diminution in the systemic depuration and renal excretion of PAH may be explained by the decrease in its filtered and secreted load. The lower OAT1 expression in remnant renal mass of CRF rats or/and the lower activity of Na-K-ATPase might justify, at least in part, the diminished secreted load of this organic anion.

Contribution of Multidrug Resistance Protein 2 (MRP2/ABCC2) to the Renal Excretion of p-aminohippurate (PAH) and Identification of MRP4 (ABCC4) as a Novel PAH Transporter

p-Aminohippurate (PAH) is the classical substrate used in the characterization of organic anion transport in renal proximal tubular cells. Although basolateral transporters for PAH uptake from blood into the cell have been well characterized, there is still little knowledge on the apical urinary efflux transporters. The multidrug resistance protein 2 (MRP2/ABCC2) is localized to the apical membrane and mediates ATP-dependent PAH transport, but its contribution to urinary PAH excretion is not known. In this report, we show that renal excretion of PAH in isolated perfused kidneys from wild-type and Mrp2-deficient (TR(-)) rats is not significantly different. Uptake of [(14)C]PAH in membrane vesicles expressing two different MRP2 clones isolated from Sf9 and MDCKII cells exhibited a low affinity for PAH (Sf9, 5 +/- 2 mM; MDCKII, 2.1 +/- 0.6 mM). Human MRP4 (ABCC4), which has recently been localized to the apical membrane, expressed in Sf9 cells had a much higher affinity for PAH (K(m) = 160 +/- 50 microM). Various inhibitors of MRP2-mediated PAH transport also inhibited MRP4. Probenecid stimulated MRP2 at low concentrations but had no effect on MRP4; but at high probenecid concentrations, both MRP2 and MRP4 were inhibited. Sulfinpyrazone only stimulated MRP2, but inhibited MRP4. Real-time PCR and Western blot analysis showed that renal cortical expression of MRP4 is approximately fivefold higher as compared with MRP2. MRP4 is a novel PAH transporter that has higher affinity for PAH and is expressed more highly in kidney than MRP2, and may therefore be more important in renal PAH excretion.

Compensation Increase in Organic Anion Excretion in Rats with Acute Biliary Obstruction: Role of the Renal Organic Anion Transporter 1

The purpose of the present study was to examine in rats the effects of acute bile duct ligation on the expression of the organic anion transporter 1 in the kidney and the consequences of these effects on the systemic clearance of organic anions, particularly on p-aminohippurate (PAH) clearance, since it has been viewed as the prototypic organic anion. Male Wistar rats underwent bile duct ligation (BDL rats). Pair-fed sham-operated rats served as controls. All studies were carried out 21 h after surgery. Our data revealed that BDL rats had a higher expression of organic transporter 1 protein in kidney cortex homogenates. Accordingly, systemic clearance of PAH and urinary excretion of PAH were both higher in BDL rats. These findings suggest that impairment of the liver function after BDL is followed by a distinct and statistically significant increase in renal excretion of PAH, indicating a possible compensation mechanism.

RT-PCR-based evidence for the in vivo stimulation of renal tubular p-aminohippurate (PAH) transport by triiodothyronine (T3) or dexamethasone (DEXA) in kidney tissue of immature and adult rats

Our previous studies have shown that a pre-treatment of rats with triiodothyronine (T3) or dexamethasone (DEXA) increases renal PAH excretion significantly. This stimulation was accompanied by an enhanced protein synthesis within the renal cortex. To explore the molecular basis for this sub-chronic induction process, we investigated the stimulation of PAH accumulation in renal cortical slices as well as the expression level of organic anion transporter 1 (OAT1), the recently cloned renal basolateral PAH-transporter, using RT-PCR techniques under the applied conditions. 10- and 55-day-old Han:WIST rats were treated in vivo with T3 (20 microg/100 g b.wt.) or DEXA (60 microg/100 g b.wt.), both for 3 days, once daily. Renal cortical slices were incubated for 2 hours in Cross-Taggart medium and PAH uptake into kidney tissue was measured time dependently (slice to medium ratio, QS/M). The accumulation capacity is comparable between immature and mature rats (control-QS/M: 6.7 +/- 0.1 vs. 6.9 +/- 0.2, respectively). Both age groups showed a significant increase of PAH accumulation capacity after T3 treatment (10-day-old rats: 15.0 +/- 0.2; 55-day-old rats: 11.7 +/- 1.3). After DEXA pre-treatment, PAH accumulation was only slightly changed (10-day-old rats: 5.9 +/- 0.2; 55-day-old rats: 8.2 +/- 1.3). Semi-quantitative measurements of OAT1 mRNA expression level showed a significant increase of OAT1 mRNA after pre-treatment with both T3 and DEXA in the two age groups. Thus, this is the first evidence that T3 and DEXA pre-treatment induces the expression of OAT1.

Renal excretion and renal tubular transport of p-aminohippurate (PAH) in methimazole treated, hypothyroid rats of different ages

Thyroid hormone deficiency following treatment with methimazole for 7 days does not reduce PAH secretion in renal tubular cells as expected from data in thyroid hormone treated rats. This treatment with methimazole causes an increase in renal excretion of PAH in rats of various age groups, statistically significant in 5-, 10- and 20-day-old rats. In 20-day-old, methimazole treated rats the increase in renal excretion of PAH is obviously caused by a higher transport rate in renal tubular cells, proved also in 33-day-old rats. An increased filtered fraction of PAH in 5- and 10-day-old rats could be the reason for the rise in renal excretion of PAH after repeated treatment with methimazole. The mechanism of renal effects of methimazole treatment remains unclear.

Postnatal development of sex differences in renal tubular transport of p-aminohippurate (PAH) in rats.

Compared with female rats a distinctly higher rate of accumulation of p-aminohippurate (PAH) in renal cortical slices from mature male rats can be proved; there are no sex differences in young rats with immature kidney function. Postnatal development of sex differences in kidney weight shows the same pattern. The lack of sex differences in the renal excretion of PAH in all age groups could be caused by a higher fraction of glomerularly filtered PAH in female rats. In mature male rats the high rate of tubular transport of PAH can be diminished by castration or by blockade of testosterone receptor sites (treatment with cyproterone). Stimulation of PAH transport by repeated treatment with testosterone is more expressed in male than in female rats. Furthermore, estrogens seem not to be responsible for sex differences in renal tubular transport of PAH (no influence of ovarectomy, low effects of treatment with estradiol in male rats).

Influence of sympathetic nervous system on dexamethasone-stimulated renal tubular transport of p-aminohippurate in young rats.

After simultaneous administration of dexamethasone together with 6-hydroxydopamine or adrenergic neuronal blocking agents (alpha-methyldopa, reserpine, guanethidine) the dexamethasone-stimulated increase in renal excretion of p-aminohippurate (PAH) is distinctly diminished. The same is true for dopamine. This depressive effect could be proved by measurement of transport rates of PAH in renal cortical slices in vitro. The increase in kidney weight and in the protein content of kidney tissue in dexamethasone-treated rats is lower in rats simultaneously treated with adrenergic neuronal blocking agents of 6-hydroxydopamine. Adrenoceptor agonists and antagonists (pholedrine, orciprenaline, phentolamine, propranolol) are without influence on the dexamethasone-stimulated increase in PAH transport.

Stimulation of renal tubular transport of p-aminohippurate in rats of different ages by treatment with adrenocortical steroids.

Treatment with prednisolone or dexamethasone is followed by an increase in renal excretion of p-aminohippurate (PAH) and in accumulation of PAH in renal cortical slices, particularly in 5- and 10-day-old rats with immature kidney function. Treatment with triamcinolone is effective both in immature and in 55-day-old rats. There is no stimulation of PAH transport after treatment with mineralocorticoids (desoxycorticosterone, aldosterone).

Effects of Prenatally Administered Thyroid Hormones or Glucocorticoids on Maturation of Kidney Function in Newborn Rats

Influences of treatment with thyroid hormones or dexamethasone during pregnancy on development of kidney function were studied in newborn rats. Treatment of dams for 3 days is followed by a higher rate of urine production in newborn rats. A statistically significant raise of sodium/potassium ratio in tetraiodothyronine- or dexamethasone-treated rats indicates a higher degree of maturation of kidney function. Treatment of dams with dexamethasone is followed by an increase of absolute excreted quantities of sodium and potassium in newborn rats. Treatment of dams with triiodothyronine can increase renal excretion of p-aminohippurate in newborn rats.

Age-related differences in nephrotoxicity of cadmium

Nephrotoxic effects can be quantified by measurement of renal excretion of p-amino-hippurate (PAH). Intraperitoneal administration of cadmium in increasing single doses to adult rats is followed by a biphasic effect on renal PAH excretion. Administration of low doses (250 or 500 micrograms/100 g b.wt. CdCl2) results in a significant increase whereas a single dose of 750 micrograms/100 g b.wt. CdCl2 is followed by a distinct diminution of renal PAH excretion. Repeated administrations of 500 micrograms/100 g b.wt. CdCl2 for 2 or 3 consecutive days result in a marked reduction of PAH excretion which is reversible 5 or 6 d following administration. In juvenile rats cadmium does not produce any statistically significant alteration in renal PAH excretion, likely caused by the immaturity of renal tubular transport processes.

Influence of inhibitors of protein synthesis on restitution of tubular transport capacity after unilateral nephrectomy

One day after unilateral nephrectomy (uNX), excretion of p-aminohippurate (PAH) reaches 80% of control values in rats. A stimulation of tubular transport by repeated administration of xenobiotics shortened the phase of diminished PAH excretion capacity following. The relative extent of compensation (%) after uNX is not affected significantly by inhibitors of protein synthesis. These inhibitors influence the time course of compensation after uNX. Administration of azauracil, fluorouracil and neomycin, respectively, causes a dose dependent reduction of PAH excretion in nephrectomized and sham operated animals. This effect is also provable following pretreatment with cyclopenthiazide, which can stimulate the PAH elimination. A stimulated renal function after uNX can also be suppressed by high doses of inhibitors of protein synthesis. In contrast to this, small doses of these substances produce a stimulation of renal PAH excretion. The extent of this stimulation reached the same degree as after cyclopenthiazide pretreatment found in preliminary experiments. An additional treatment with cyclopenthiazide does not additionally increase PAH excretion. These results indicate that processes of compensatory growth as well as induction of renal tubular transport are caused by increased protein synthesis.

Stimulation of kidney function in rats of different ages injured by nephrotoxic agents

Intensity and duration of nephrotoxic effects can be characterized by measurement of renal p-aminohippurate (PAH) excretion. Single administration of potassium dichromate or glycerol is followed by a marked decrease of renal PAH excretion in dependence on the time after the administration as well as on the dosage used. Both agents are without effect in young rats with an immature tubular transport system for organic anions. As observed previously in rats with intact kidney function, renal PAH excretion can also be stimulated in rats with potassium dichromate or glycerol induced kidney damage. Stimulation of renal PAH excretion is possible in injured rats by repeated administrations of PAH and cyclopenthiazide, respectively. Exactly, the duration of injury is shortened whereas the intensity of the nephrotoxic effect is not changed. However, this effect depends on the age of rats as well as on the nephrotoxic agent administered.