4-Maleimidohippuric acid--a tailor-made, direct, site-specific nephrotoxin: effects on renal function and ultrastructure in pentobarbital-anesthetized dogs.

A model has been proposed to explain at least one of the possible pathways through which a xenobiotic might produce proximal tubule necrosis. The model is formulated on the idea that a compound must possess two structural features: (i) a carboxyl or amino acid moiety that would allow for selective uptake into proximal tubule cells via the strategically located antiluminal membrane-bound organic anion transport system or the luminal membrane-bound amino acid transport system(s), respectively, and (ii) a highly reactive moiety that can directly alkylate proximal tubular components, or a moiety that can be biotransformed within proximal tubular cells to such a substance. In an attempt to validate the proposed structural features as prerequisites for xenobiotic induction of proximal tubular necrosis, a novel compound, 4-maleimidohippuric acid (4-MHA), was synthesized which possesses an anionic group and a reactive moiety. Following the administration of 4-MHA directly into the renal artery of pentobarbital-anesthetized dogs, specific unilateral ultrastructural damage was noted only in the S1 and S2 cell types of the proximal tubule; the most notable renal function changes included proteinuria and glucosuria. Anionic, but non-alkylating, relatives of 4-MHA failed to alter renal function or ultrastructure. The specific proximal tubular toxicity of 4-MHA validates the proposed structural requirements for induction of proximal tubular necrosis.

Citrinin produces acute adverse changes in renal function and ultrastructure in pentobarbital-anesthetized dogs without concomitant reductions in [potassium]plasma.

Citrinin's nephrotoxicity was examined in pentobarbital-anesthetized dogs under conditions that minimized or avoided significant changes in a number of its actions that could indirectly and adversely affect renal function and ultrastructure, such as, (i) major acute reductions in blood pressure and renal blood flow and, (ii) emesis and diarrhea that could lead to dehydration and electrolyte imbalances, especially hypokalemia. Slow intravenous injection of 20 mumol citrinin/kg to pentobarbital-anesthetized dogs did not induce any alterations in renal tissue ultrastructure or in any of the 23 whole blood, plasma or renal function parameters that were monitored over a 6-h post-citrinin period. On the other hand, 80 mumol citrinin/kg produced significant increases in the hematocrit and in the renal excretion rates of protein and glucose; modest reductions were noted in CIN, RBF and excretion rate of inorganic phosphorus. In addition, 80 mumol citrinin/kg induced ultrastructural lesions in the cells of the S2 proximal tubular segment, the thick ascending limb, the distal convoluted tubule and the collecting ducts. The glomeruli, S1 and S3 cells of the proximal tubule and the thin descending and ascending limbs of Henle's loop were unaffected by both citrinin doses. The location and nature of the adverse ultrastructural lesions were most likely the result of the direct actions of citrinin (or a citrinin metabolite) since the effects of citrinin that could lead to indirect adverse renal effects were totally avoided or greatly minimized.

The pentobarbital anesthetized dog: an animal model for assessing chemically induced changes in renal function and ultrastructure.

An experimental procedure was devised using the pentobarbital-anesthetized dog that could be used for the comprehensive evaluation of the renal effects of chemicals. After IV or renal arterial administration of 0.9% saline solution (vehicle), 12 renal function determinants were continuously monitored for periods of 2 and 6 hours. At the completion of the 2 or 6 hours of study, the kidneys of a number of dogs (usually between 1 and 7) in each vehicle-treated group were subjected to a modification of the intravascular perfusion-of-fixative technique to evaluate the ultrastructural status of the outer cortical, inner cortical, and outer medullary tissue. The remaining dogs (at least 3) in each vehicle-treated group were given a nonnephrotoxic, but maximally effective, diuretic dose of ethacrynic acid, which enabled an assessment of the functional integrity of the thick ascending limb of Henle's loop. Renal function and glomerular and tubular ultrastructure remained stable in the pentobarbital-anesthetized dog for up to 6 hours after administration of vehicle. Sustained infusion of inulin (included in the procedure to estimate glomerular filtration rate) throughout the duration of the experiments, and pentobarbital anesthesia of various durations did not alter the morphologic status of the canine nephron. The procedure used for the renal perfusion of fixative circumvented any manipulation of the kidneys before fixation and allowed for the acquisition of normal (unaltered) appearing tissue from all areas of the kidneys. The responses of pentobarbital-anesthetized dogs to ethacrynic acid administration were similar when given 2 and 6 hours after the vehicle administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a semi-automated blood urea nitrogen analyzer.

We compared results for urea concentrations in plasma and serum as measured with the Kimble Blood Urea Nitrogen Analyzer method as the test method with those determined by continuous-flow analysis (AutoAnalyzer 1 method) as the comparison method. We evaluated accuracy and precision for patients' samples, National Bureau of Standards Standard Reference Material, College of American Pathologists Survey Validated Reference Materials, and College of American Pathologists Quality Assurance Service control materials. We found the test method to be more accurate and precise than the comparison method.

Acute effects of alkylating agents on canine renal function and ultrastructure: high-dose ethacrynic acid vs. dihydroethacrynic acid and ticrynafen.

Ethacrynic acid (EA) is unique among diuretics in that it is both an avid alkylating agent and is actively secreted by renal proximal tubular cells. EA might therefore be expected to produce detrimental proximal tubular changes at elevated doses. Because of this possibility, we examined the renal effects of two relatively high doses of EA (i.e., 66 and 151 mumol/kg i.v.) and an equivalent high dose (i.e., 151 mumol/kg) of two nonalkylating relatives of EA [dihydro-EA (EA-H2) and ticrynafen]. Twelve renal function parameters were monitored in pentobarbital-anesthetized dogs for a period of 2 hr after administration of EA, EA-H2 and ticrynafen and renal tissue was acquired at the end of the 2 hr of study for light and electron microscopic evaluation. Both doses of EA produced a profound diuresis of similar magnitude. However, only the larger dose was associated with a concomitant reduction in the glomerular filtration rate, a downward trend in the renal blood flow, a proteinuric response in four of the seven dogs in the treatment group and a reproducible vacuolation of the initial portion of the proximal convoluted tubules (i.e., the S1 cells). EA-H2 induced a small, transient increase in the excretion rates of sodium, chloride and potassium, but failed to elicit a proteinuric response or alter proximal tubular ultrastructure. Ticrynafen, a far more efficacious diuretic agent than EA-H2, likewise failed to trigger a proteinuric response or changes in renal ultrastructure. The combination of acidic (anionic) and alkylating properties of EA is thought to be responsible for the proximal tubular effects observed in this study.