Metabolic studies of HgCl2-induced acute renal failure in the rat

Plasma Clearance of Intravenously Infused Adrenomedullin in Rats with Acute Renal Failure

Plasma adrenomedullin concentrations are reportedly elevated in patients with renal failure; however, the underlying mechanism is unclear. In this study, we investigated the plasma clearance of synthetic human adrenomedullin (AM) in two models of rats with renal dysfunction; one was induced by subcutaneous injection of mercury chloride (RD-Ag) and the other by completely blocking bilateral renal blood flow (RD-Bl). Sixty minutes after starting intravenous AM infusion, AM levels in RD-Ag, RD-Bl, and rats with normal renal function (NF) were still increased slightly; however, plasma AM levels in RD-Ag rats were approximately three times as high as in RD-Bl and NF rats. Plasma AM disappearance after the end of treatment was similar among the three groups. Pharmacokinetic analysis revealed that elevated plasma AM in RD-Ag rats may be caused by a reduced volume of distribution. The adrenomedullin functional receptor is composed of heterodimers, including GPCR, CLR (calcitonin receptor-like receptor, CALCRL), and the single transmembrane proteins, RAMP2 or RAMP3 (receptor activity modifying protein). Calcrl expression was downregulated in the lungs and kidneys of RD-Ag rats. Furthermore, the plasma concentration of exogenous AM was elevated in mice deficient in vascular endothelium-specific Ramp2. These results suggest that decreased plasma AM clearance in RD-Ag is not due to impaired renal excretion but to a decreased volume of distribution caused by a reduction in adrenomedullin receptors.

Distribution kinetics of inorganic mercury in the subcellular fractions of fish liver

The present study tries to find out the kinetics of distribution of mercury in the different subcellular fractions of the liver in a freshwater perch Anabas testudineus over a period of 48 h after a single i.m. injection of [203Hg]mercuric nitrate at a dose of 4 mg/kg body weight. The fish were killed at 15 min, 2 h, 6 h and 48 h post injection. In addition the interaction of this metal with different biomolecules, viz., protein, DNA and RNA, was also investigated. Cytosol was found to be the major site of mercury accumulation. Moderate amounts of accumulation occurred in the nuclear, mitochondrial and microsomal fractions, although varying with time, while the lysosomal fraction did not reveal any spectacular retention of mercury. A significant increase in the protein content of nuclear, mitochondrial, lysosomal and cytosolic fractions was also noticed at different time periods of mercury injection. In the nuclear, microsomal and cytosolic proteins, mercury binding increased more significantly over time than the mitochondrial and lysosomal proteins. A biphasic binding pattern of mercury was seen in nuclear and mitochondrial DNA and mitochondrial and cytosolic RNA.

Disposition of quinine in rats with induced renal failure

Aetiologically different models of experimental acute renal failure were induced in rats by the administration of glycerol, mercuric chloride and gentamicin, respectively, to different groups. Quinine levels in plasma and urine of the rats with induced renal failure were determined and pharmacokinetic parameters (elimination t1/2, CLp, V, CLR AUC0-infinity) of the drug were derived and compared with values obtained from control rats following intraperitoneal administration of a 10 mg/kg body-weight dose of quinine. Results showed that each of the three compounds caused an up to 25-fold increase in the plasma levels of the drug and a marked decrease in the levels of the metabolite 3-hydroxyquinine. All the pharmacokinetic parameters determined for the rats with renal impairment were markedly different when compared to control. The high plasma quinine levels observed in the rats with renal failure could be largely due to the marked decrease in V and reduced metabolism. Also, in the rats with renal impairment, no correlation was observed between the increased plasma urea levels and plasma quinine levels or disposition of the drug. The results of the study suggest that quinine should be used with caution in patients with renal impairment. The plasma urea levels, as a measure of renal function, might not provide a suitable index for determining quinine dosage.

Renal epithelial amino acid concentrations in mercury-induced and postischemic acute renal failure

The concentration of 18 alpha-amino acids (AAs) in plasma and renal cortical cell water were measured 3 or 24 hr after 1 hr of unilateral renal artery clamping or 24 or 48 hr after 15 mg/kg body weight HgCl2 injection sc as a test of epithelial integrity. Cellular glycine (Gly), hydroxyproline (Hpr), ornithine (Orn), phenylalanine (Phe), serine (Ser), and tryptophan (Trp) concentrations were depressed 24 hr after HgCl2 (p less than 0.05), but the remaining 12 AAs were not distinguishable from control despite the presence of severe renal failure. ARginine (Arg), glutamic acid (Glu), and valine (Val) also were decreased (P less than 0.05) 24 hr later, but concentrations of half of all measured AAs were still normal. Cellular alanine (Ala), Arg, Glu, Gly, Phe, and Ser concentrations were decreased 3 hr after ischemia, p less than 0.05, but 12 AAs were unchanged and only Arg, Phe, Ser, and threonine (Thr) were reduced 24 hr after ischemia was reversed. Concentrations of even the most affected AAs remained notably higher than in plasma in both forms of acute renal failure (ARF). Total loss of AAs from a small proportion of tubular cells would be hidden by essentially normal concentrations in the rest, and such losses may well have occurred. Unless cellular AAs in ARF are almost completely bound, however, the well-maintained cell:plasma AA concentration ratios indicate that cellular energetics were adequate for AA uptake and that epithelial permeability to AAs in the vast majority of cells was not greatly disturbed. Such findings suggest that most of the epithelium, although seriously damaged, had remained viable.

Extracellular Ca2+-dependent elevation in cytosolic Ca2+ potentiates HgCl2-induced renal proximal tubular cell damage

While normal fluctuations of cytosolic Ca2+ ([Ca2+]i) occur physiologically, the deregulation of cellular Ca2+ homeostasis leads to cellular injury. The contribution of [Ca2+]i to the process of cellular damage was assessed in a model system where HgCl2 was used to induce plasma membrane damage in renal tubular cells. In the presence of 1.37 mM extracellular Ca2+, HgCl2 (10-50 microM) induced a slow, dose-dependent, 4-6 fold increase in [Ca2+]i (as measured by Quin 2) by 10 min of exposure, which could be abolished by prior incubation of the cells with dithiothreitol. Correlates of cellular injury, i.e., decrease in cell viability, change in cellular morphology, such as bleb formation, membrane distortion and mitochondrial swelling, were induced after HgCl2 addition. The rate and dose-responses of these changes were similar to that of [Ca]i elevation. When cells were exposed to HgCl2 in the absence of added extracellular Ca2+, there was no increase in [Ca2+]i and both the rate and extent of cell damage were reduced. When Ca2+ was readded to the extracellular medium after HgCl2, there was a rapid elevation of [Ca2+]i, increased cell killing and bleb formation. The observed correlation between [Ca2+]i elevation, decreased cell viability and morphological aberrations in terms of (i) dose-dependency for HgCl2, (ii) requirement for high extracellular Ca2+, and (iii) rate of change, suggests that HgCl2-induced renal cell damage involves the entry of Ca2+ from the extracellular milieu which potentiates the progression of cellular injury.

Protective effect of sodium molybdate on the acute toxicity of mercuric chloride. V. Enhancement of renal regeneration after exposure to HgCl2

Pretreatment with Na2MoO4 protected rats from HgCl2-induced decreases in the renal concentration of amino acids, RNA, DNA, ATP and dry matter. It also reduced the mercury-induced increases in renal water, Ca and serum creatinine. Ma2MoO4 considerably elevated the RNA/DNA ratio in the renal cortex after treatment with HgCl2. In addition, subcellular distribution of mercury was markedly altered by pretreatment with Na2MoO4, specifically Na2MoO4 pretreatment decreased the mercury content in the particulate fractions such as the nuclei and mitochondria while increasing the mercury content of the cytosol. Sephadex G-75 gel filtration showed that the increase in mercury content in the cytosol of Na2MoO4-pretreated rats is due to an increase in the metal content of a metallothionein-like fraction. These results suggest that Na2MoO4-pretreatment protects against HgCl2 renal toxicity by stimulating mercury-mediated metallothionein induction in the renal cortex and renal regenerative processes.

HgCl2-induced changes in cytosolic Ca2+ of cultured rabbit renal tubular cells

Fura 2 was used to measure changes in cytosolic [Ca2+] ([Ca2+]i) in cultured rabbit kidney proximal tubule cells exposed to HgCl2. Treatment with 2.5-10 microM HgCl2 resulted in an extracellular [Ca2+] ([Ca2+]e)-independent 2- to 12-fold increase in [Ca2+]i above resting levels of about 100 nM. Treatment with 25-100 microM HgCl2 caused a rapid [Ca2+]e-independent 10- to 12-fold increase in [Ca2+]i within 1 min followed by a recovery to about 2-fold steady state by 3 min. With 25-100 microM HgCl2, both magnitude and rate of Ca2+ increase were similar, but recovery was greater with increasing doses. A slower, secondary increase in [Ca2+]i followed which varied with HgCl2 concentration and required [Ca2+]e. The first increase in [Ca2+]i represents release from intracellular pools. Calcium channel blockers, calmodulin inhibitors, and mitochondrial inhibitors do not alter the patterns of [Ca2+]i changes due to HgCl2. The recovery response with higher HgCl2 concentrations appears to be triggered by Hg2+ and not by the increased [Ca2+]i. Sulfhydryl modifiers N-ethylmaleimide, PCMB and PCMBS produced [Ca2+]e-independent [Ca2+]i increases similar to those induced by low HgCl2 concentrations. Cell killing with HgCl2 was about 50% greater with normal [Ca2+]e than with low [Ca2+]e, suggesting that [Ca2+]e influx is important in accelerating injury leading to cell death.

Metabolic studies of postischemic acute renal failure in the rat

Postischemic acute renal failure was induced by 1 hr of clamping of the renal vasculature. Adenine nucleotide (ATP, ADP, AMP) and lactate (Lac) levels were measured after 0, 0.25, 1, 6, 24, and 48 hr of reflow to determine the time necessary for recovery to control levels. After 1 hr of ischemia with no reflow, [ATP] was 18% and [Lac] was 10-fold control levels. Control levels were restored after 24 hr of reflow. Variable ischemic times (5, 15, 30, 60, 90, and 120 min) followed by (1) no reflow or (2) 24 hr of reflow were also studied. [ATP] decreased to 25 and 13% of controls after 5 and 120 min of ischemia, respectively, and [Lac] increased to 5- and 13-fold controls after 5 and 120 min. Five to ninety minutes of ischemia followed by 24 hr of reflow resulted in a trend toward restoration of ATP and Lac levels; whereas, 120 min of ischemia followed by 24 hr of reflow resulted in death. The results indicate that: (1) In vivo ischemia results in a drastic and rapid shift in the ATP-ADP-AMP equilibrium; (2) the absolute concentration of ATP is not a reliable criterion of cell viability, but the ability to resynthesize ATP may be determinant in the reversibility of the lesion; (3) 1 hr of ischemia is reversible with respect to restoration of [ATP] and [Lac], but 24 hr of reflow are needed for restoration; and (4) ischemia for 90 min results in a metabolic derangement which is partially reversible in that metabolite levels are partially restored after 24 hr of reflow. However, 90 min of vascular clamping is not functionally reversible since the majority of animals exhibit severe azotemia and do not survive.

Methods in testing interrelationships between excretion of drugs via urine and bile

The liver and kidney are largely responsible for inactivating and eliminating drugs and other chemicals. As the excretory capabilities of the two organs overlap, a damage of one system might be compensated by the other. Because of the specificity of both renal and hepatic elimination mechanisms such an alternative excretion route is not possible generally. Several interferences are possible to characterize the relation between hepatic and renal excretion of drugs and xenobiotics. Firstly, the simultaneous assay of excreted drug amounts in urine and bile can give some information concerning the main transport routes of this drug. Thereafter the total interruption of liver or kidney function elucidates the general possibility of alternative excretion routes. But it is important for clinical practice to distinguish between different localizations of organ damages. Today some experimental possibilities exist to exclude partial functions of both kidney and liver separately. Thus it can be clarified why a compound might be excreted via liver or kidney. Moreover it can be characterized whether or not a compensation for the loss of one main excretion organ is possible or not. Such investigations are of some practical importance. Dosing guidelines for drug therapy must be completed for cases of renal or hepatic failure. Moreover the developmental pattern of both elimination routes has consequences for drug use in paediatrics as well as geriatrics. Beside this point of view such investigations are necessary for the prediction of changes in the toxicity of drugs after renal or hepatic insufficiency.

Effects of ochratoxin A in the partially nephrectomized rat

The effects of ochratoxin A (OA), a nephrotoxic mycotoxin, were investigated in partially nephrectomized (PN) rats (approximately 70% reduction in renal mass) following compensatory hypertrophy of the renal remnant. Renal function stabilized 27 d after surgery. PN rats compensated for the initial loss of renal function except for glomerular filtration rate (GFR, inulin clearance); this remained significantly impaired. Sham-operated (SO) rats cleared inulin and p-aminohippurate (PAH) at rates of 3.84 and 7.49 ml/min, respectively, while compensated PN rats cleared inulin at 2.51 and PAH at 8.84 ml/min. Daily administration of low levels of OA produced decreased urine osmolality and body weight with a modest increase in urinary protein of PN versus SO rats. OA-treated rats cleared inulin, creatinine, and PAH at rates significantly lower than nontreated controls: 0.89 and 1.96 ml/min for inulin, 0.35 and 0.56 ml/min for creatinine, and 2.29 and 6.23 ml/min for PAH. Histopathological findings indicated a considerable increase in renal tubular necrosis and subcellular damage (i.e., loss of cytoplasmic ground substance, vacuolization, degeneration of mitochondria, and reorganization of endoplasmic reticulum) in PN animals versus controls, concurrent with alteration in renal function. These results verify that the nephrotoxic action of OA is elicited mainly in renal proximal tubules and is enhanced in the PN rat.

Toxicity of mercuric chloride to the developing rat kidney. I. Postnatal ontogeny of renal sensitivity

Although the sensitivity of the adult rat kidney to mercuric chloride has been widely reported, the degree to which this toxicant affects the developing kidney is unknown. Therefore, this study examined the effects of HgCl2 on renal function during postnatal maturation. Sprague-Dawley rats were treated with a single sc injection of 5 mg/kg HgCl2 on Day 1, 8, 15, 22, or 29 after birth. The effects on renal function, histology, and morphology were assessed 24, 48, and 120 hr after each treatment. Measurements of renal function included urine volume, osmolality, the ability to concentrate urine during water deprivation, urinary pH, chloride and protein content, tests for glucosuria, hematuria, and various serum chemistry parameters. Rats were killed and their kidneys processed and examined by light microscopy. The renal sensitivity to HgCl2 increased throughout maturation for every parameter measured. No pups treated with HgCl2 on Day 1 died, but mortality increased to almost 20% in rats treated 22 and 29 days after birth. Body weight was unaffected in Day 1 animals, but was decreased at 120 hr post-treatment in three of the other four age groups. Kidney weights were unaffected in 1- and 8-day olds, but were increased by 10 to 55% in rats that were 15, 22, and 29 days old. Urine volume was increased 48 to 72 hr following treatment at all ages. The ability to concentrate urine in response to water deprivation was compromised in all animals with the exception of those treated on Day 1, and was decreased to the greatest extent in 29-day-olds. Urinary chloride concentration was decreased in Day-22 animals at 24 and 48 hr, and in Day-29 rats at all times observed after injection. Urinary pH was more acidic in treated suckling pups, and more basic in treated pups after weaning on Day 22. Urinary protein content was increased after exposure in all but the pups treated on Day 1. Serum creatinine was increased at 120 hr after injection in Day-8 rats, and 24 and 48 hr after injection in older rats. Glucosuria and hematuria occurred with increasing frequency as the pups matured. Histological evaluation revealed some cortical tubular dilatation in rats treated on Day 1 or Day 8; there was tubular necrosis in older rats. For all parameters observed, the neonatal kidney was largely insensitive to HgCl2 toxicity; however, a trend toward increased sensitivity with increasing age was demonstrated.