Relation between renal and hepatic excretion of drugs: III. Comparison of various methods reducing the renal or hepatic excretory capacity of rats

Suitability of 5/6 nephrectomy (5/6NX) for the induction of interstitial renal fibrosis in rats--influence of sex, strain, and surgical procedure

Chronic renal failure (CRF) is a serious clinical problem and currently there are no adequate therapeutic strategies for treatment. Many possible treatment strategies have been tested in rats with CRF induced by subtotal nephrectomy. However, reports in the literature concerning the consequences of this procedure on rat kidney function are contradictory. For instance, such an intervention in male Sprague-Dawley rats apparently initiates the development of interstitial renal fibrosis, while in our similar studies on female Wistar rats (HW) there was minimal renal fibrosis. Therefore, we carried out experiments in adult rats to investigate the long-term consequences of 5/6 nephrectomy (5/6NX) in relation to (1) sex, (2) strain, and (3) two methods of surgical ablation. Ten weeks after 5/6NX, body weight gain, systolic blood pressure, creatinine clearance, and urinary protein were measured, along with renal hydroxyproline concentration determinations to assess the deposition of extracellular matrix. Also, light microscopic investigations were done to characterize renal damage. The functional parameters clearly indicated the development of CRF, while morphologic investigations showed only moderate fibrotic areas containing atrophic tubules and lymphocytic infiltrates. However, 45-60% of glomeruli were sclerotic. In summary, 5/6NX, using either method of partial nephrectomy, induces signs of moderate glomerulonephritis preferentially in female HW rats. Thus 5/6NX in female HW rats can be recommended as a suitable model in the induction of renal fibrosis.

Intestinal Absorption and Hepatic Extraction of Propranolol and Metoprolol in Rats with Bilateral Ureteral Ligation

To investigate the mechanism responsible for the increased bioavailability of propranolol in bilateral ureter-ligated (BUL) rats, the intestinal absorption and hepatic extraction of propranolol and metoprolol were evaluated. The initial absorption rate of these drugs after intra-intestinal administration was only slightly increased in the BUL rats, whereas the blood drug concentration in these rats was higher than that in control rats. The blood propranolol and metoprolol concentrations during intra-portal infusion in the BUL rat were significantly higher than that in the control rat. In the presence of NADPH, the intrinsic metabolic activity of metoprolol in hepatic microsomes was not altered by BUL. On the other hand, the NADPH generation rate in the hepatic cytosol in the BUL group was lower than that in the control group. These results indicate that the absorption rate-dependent decrease in hepatic first-pass clearance of propranolol and metoprolol due to saturation kinetics is marginal, and that the hepatic metabolic activity and extraction of the drugs is significantly decreased in BUL rats probably due to the reduced NADPH generation rate in the liver.

Renal handling of amino acids in 5/6-nephrectomized rats: stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone under amino acid load

In anaesthetized adult female rats, the renal amino acid handling was measured six days after 5/6 nephrectomy (5/6NX). The distinct rise in blood urea nitrogen as well as the significant reduction in urine flow and GFR indicate an impairment of kidney function. In principle, in 5/6NX rats amino acid plasma concentrations were comparable to those of control animals with two intact kidneys, whereas the fractional excretions (FEAA) of most endogenous amino acids measured were significantly enhanced. After bolus injection of leucine or taurine (each 20 mg/100 g b.wt.) or glutamine (90 mg/ 100 g b.wt.), dissolved in 2 ml normal saline per 100 g b.wt., the FEAA of both the amino acids administered and the endogenous amino acids increased as a sign of overloaded amino acid reabsorption capacity. This effect was more pronounced in 5/6NX rats than in controls. As early as one hour after amino acid load, plasma concentrations and FEAA returned to baseline values of 5/6NX rats. A pretreatment with triiodothyronine (20 micrograms/100 g b.wt.) or dexamethasone (60 micrograms/100 g b.wt.), both given intraperitoneally once daily for 3 days, stimulated the renal amino acid transport capacity in 5/6NX rats: the increase in FEAA after amino acid load was significantly lower compared to non-pretreated animals. This stimulation could be shown for the bolus amino acids and the endogenous amino acids and was more distinct in 5/6NX rats than in controls with two intact kidneys.

The hepato-renal syndrome: renal amino acid transport in bile duct ligated rats (DL)--influence of treatment with triiodothyronine or dexamethasone on renal amino acid handling in amino acid loaded rats

The influence of triiodothyronine or dexamethasone on renal amino acid handling was investigated in anaesthetized, bile duct-ligated (DL) adult female rats. 3 days after DL, glomerular filtration rate (GFR) was unchanged whereas urine flow was decreased. Plasma concentrations of 5 out of 16 amino acids were significantly enhanced after DL. On the other hand, the fractional excretion (FE) of 11 out of 16 amino acids was significantly reduced as a sign of improved reabsorption capacity. Bolus injections of leucine (20 mg/100 g b.wt.), glutamine (45 mg/100 g b.wt.), or taurine (45 mg/100 g b.wt.) were followed by a temporary increase in the FE of the administered amino acids as well of the endogenous amino acids which were not administered. This phenomenon was more pronounced in DL than in control rats. Under load conditions, dexamethasone (60 microg/100 g b.wt.) or triiodothyronine (20 microg/100 g b.wt.) treatment for 3 days, i.p. once daily, was followed by a stimulation of renal amino acid reabsorption in DL rats. The increase in fractional amino acid excretion after amino acid load was significantly lower than in untreated rats. This effect was also more pronounced in DL rats.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Relation between renal and hepatic excretion of drugs. XIV. Elimination of ioglycamic acid after nephrectomy, bile duct ligation, and after treatment with hormones or xenobiotics in young and adult rats

Ioglycamic acid (IGA) is effectively eliminated in young and adult rats via urine and bile. After administration of low doses hepatic excretion dominates whereas following high supply renal elimination surpasses biliary excretion. Hepatic transport of IGA is active, indicated by the occurrence of a transport maximum in vivo and by a distinct accumulation of this drug within liver slices in vitro. Renal removal of IGA is preferentially caused by glomerular filtration. A tubular reabsorption obviously does not occur because forced diuresis (mannitol, furosemide) does not increase renal excretion of this substance. As calculated from our clearance data and as a result of accumulation experiments in vitro on renal cortical slices the active tubular secretion of this organic anion can be excluded. In principle there are no qualitative changes in IGA elimination between the 20th and 55th day of life, but active hepatic transport of the drug is significantly lower in young, immature rats. After bile duct ligation, renal excretion of IGA increases distinctly in both age groups, whereas in adult rats bilateral nephrectomy (NX) is followed by a significant decrease in its hepatic excretion in dependence on time after kidney removal. In young rats NX is without consequences on hepatic excretion of IGA. It is possible to stimulate renal and/or hepatic excretion of IGA by repeated administration of T3, dexamethasone, or phenobarbital. The effect of stimulation is different in kidney and liver and depends on age, too.

Relation between renal and hepatic excretion of drugs: XIII. Pharmacokinetics of new antiarrhythmic drug Bonnecor in rats with normal and impaired excretory functions

The clearance of 14C-Bonnecor, a weak organic cation, was measured in anaesthetized rats during 6 h after administration. The drug and its labelled metabolites are excreted both via kidney and liver. The renal excretion dominates especially following high doses. After bile duct ligation the renal excretion of Bonnecor increases significantly whereas in nephrectomized rats the biliary excretion of this substance is distinctly reduced. Plasma protein binding ratios amount to 60-70%. Renal removal of Bonnecor and the formed metabolites is in part a result of glomerular filtration. Increased urinary excretion of 14C-Bonnecor-activity under conditions of forced diuresis indicates the involvement of tubular reabsorption in renal handling of the drug and its metabolites. These in vivo results could be confirmed in experiments on renal cortical slices indicating a distinct tubular transport of the drug and its metabolites. In the kidney the aerobic accumulation of Bonnecor is very effective. Surprisingly, under anaerobic incubation conditions, uptake of Bonnecor into renal tissue remains relatively high indicating a distinct binding of Bonnecor within the tubular cells. In the liver the accumulation of Bonnecor is lower compared to the kidney. Furthermore, enterohepatic circulation of Bonnecor and its metabolites was checked. In animals with intact biliary tract, renal removal of 14C-Bonnecor-activity from the organism is significantly higher than in rats with bile duct cannulation. Reinfusion of bile increased renal excretion of 14C-Bonnecor-activity additionally. Both results indicate an effective intestinal reabsorption and enterohepatic circulation of this drug.

Relation between renal and hepatic excretion of drugs: VII. Hepatic and renal excretion of phenol red in thioacetamide-induced acute and chronic liver damage

Acute and chronic liver damage was induced in rats by thioacetamide (TAA). Centrilobular liver cell damage associated with an accumulation of lipid droplets was produced by a single high dose (10 mg TAA/100 g b.m.). Liver fibrosis, micronodular and macronodular liver cirrhosis were induced by chronic TAA treatment (300 ml/l drinking water for 1.5, 3 or 6 months). Acute administration of TAA caused a significant decrease of hepatic phenol red excretion but no compensatory increase of its urinary excretion. In contrast, 24 h after bile duct ligation renal excretion of the dye increased by about 50%. After chronic exposure to TAA for three months hepatic phenol red excretion remained reduced and renal excretion raised significantly. This compensatory increase of urinary excreted phenol red amounts did not occur after 6 months of TAA treatment, probably as a result of additional nephrotoxicity of TAA. Two weeks after cessation of TAA exposure for 3 months, hepatic and renal phenol red excretion returned to normal. Bile flow per animal increased significantly after 3 months of TAA exposure. Apparently this is due to a reduced intrahepatic reabsorption of canalicular bile in TAA-damaged liver.