Roger A. Owen

Age-Related Variations in Renal Structure and Function in Sprague-Dawley Rats

Data from 500 male and 500 female Sprague-Dawley rats used as controls in studies performed at Huntingdon Research Centre to assess the safety of drugs were sampled at 17, 30, 56, 82, or 108 weeks of age. Plasma urea nitrogen levels remained constant, except in aged males. Aging caused increased proteinuria and decreased urinary concentrating ability, in addition to increased size, weight, and degree of cortical scarring of kidneys. Chronic progressive nephropathy, first seen histopathologically at 30 weeks of age, accounted for these changes and ultimately affected 81% of male and 44% of female rats. One-fifth of two-year-old male rats had diffuse parenchymal damage and a small number also had secondary hyperparathyroidism. Other notable changes included basophilic (often colloid-filled) cortical tubules, mononuclear cell infiltrations, parenchymal and pelvic mineralization, urothelial hyperplasia, and pyelonephritis. Miscellaneous low incidence findings included one lipomatous tumour and generalized lymphosarcoma.

Strain-related Susceptibility to Nephrotoxicity Induced by Aspirin and Phenylbutazone in Rats

Single doses of aspirin induce scattered foci of necrosis of proximal tubules in some strains of rats, whereas acute or sub-acute administration of phenylbutazone causes renal papillary necrosis. Initially, using Sprague-Dawley rats of CFY and CD strains, it became clear that these rats were not as susceptible to these drugs as the literature suggested. Aspirin-induced necrosis was apparently sex-related, being seen in females but could be induced by hormone treatment in males. Male Wistar and Sprague-Dawley rats had reacted differently to administration of phenylbutazone for two weeks. Two experiments were performed with four rat strains: Wistar, Lister-Hooded, Sprague-Dawley, and Fischer-344. The rats were six weeks old at the start of the experiments. Five males and five females of each strain were gavaged with either a single dose of 1,000 mg/kg of aspirin or 200 mg/kg phenylbutazone once daily for four weeks. The drugs were suspended in methylcellulose, which was given to equal numbers of control male and female rats in each experiment. The rats were maintained under standard conditions. Blood and 18-hour overnight urine samples were collected prior to sacrifice. There were no strain-related differences in the types of renal lesions seen, however there were differences in the degrees of responses to the two drugs. With aspirin the female Fischer-344 rats were the most susceptible showing necrosis of proximal tubules of both kidneys and markedly elevated urinary protein concentration and gamma-GT activity. Other females showed less change. Male rats were affected only slightly and males of the Wistar strain were not. Thus, the greater susceptibility of female rats to aspirin-induced nephrotoxicity was confirmed. Phenylbutazone killed two female and one male Wistar rats with gastrointestinal ulceration after three doses. Fischer-344 rats also showed reaction to the drug. For these two strains the dosage was reduced to 50 mg/kg/day for the remainder of the study. At the end of the dosing period one or more rats from each strain showed renal papillary necrosis. Thus, strain differences occurred in the susceptibility of the rats to phenylbutazone but this was not seen in the nephrotoxicity profiles.

The Morphology of Juxtaglomerular Cell Hyperplasia and Hypertrophy in Normotensive Rats and Monkeys Given an Angiotensin II Receptor Antagonist

L-694,492 (DUP 532), an angiotensin II (AII) receptor antagonist, was given orally at 125 mg/kg/day to rats and monkeys for up to 6 mo to assess the effects of the compound on juxtaglomerular (JG) cells. In rats, mild JG cell hypertrophy/hyperplasia occurred and was associated with a 12-fold increase in the bromodeoxyuridine-labeling index of JG cells and a 10-fold increase in renal renin content. Ultrastructurally, intermediate cells with characteristics of both smooth muscle cells and granulated renin-producing cells as well as hypertrophied renin-synthesizing cells were seen in the afferent arterioles. In monkeys, marked hypertrophy and hyperplasia were seen with an 80% increase in JG cell numbers, mitotic activity, and a greatly increased renin content compared to controls. Three mo after drug withdrawal, an increased number of cells remained, which showed features of smooth muscle cells with essentially no renin. These results show that AII receptor antagonism stimulates increased renal renin production by hypertrophy of existing granulated cells, metaplasia of smooth muscle cells to renin-synthesizing cells, and cell proliferation. When treatment was discontinued, the renin-producing cells redeveloped the features of smooth muscle cells, but, as we have shown with enalapril (angiotensin-converting enzyme inhibitor), the increase in their number persists for at least 3 mo.

Rat Urinary Bladder Hyperplasia Induced by Oral Administration of Carbonic Anhydrase Inhibitors

The carbonic anhydrase inhibitors, acetazolamide and MK-0927, were given by oral route to male Sprague-Dawley rats at 200 mg/kg/day and 25 mg/kg/day, respectively, for up to 4 weeks. Sequential necropsies were performed and urinary bladders were examined by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Similar urinary bladder changes were seen with both compounds. SEM evidenced slight multifocal urothelial changes consisting of cell swelling, dissociation, degeneration, and exfoliation after 3 and 5 days of treatment. After 2 and 4 weeks of treatment, elevated or leafy microridges on the luminal cell surfaces were seen together with foci of swollen cells. After a 2-month-recovery-period, the urothelial surfaces were normal. LM and TEM showed multifocal vacuolation of the urothelium associated with inflammation of the underlying lamina propria after 3 and 5 days of treatment. Cellular hypertrophy and hyperplasia of the transitional epithelium was seen after a 5-day treatment, persisted without increasing severity after 2 and 4 weeks of treatment, and totally regressed after the recovery period. It was concluded that, in the rat urinary bladder, oral administration of acetazolamide and MK-0927 induced early degeneration and inflammation followed by epithelial regeneration, resulting in a reversible hyperplasia of the transitional epithelium.

Spontaneous renal disease in laboratory animals.

Publisher Summary This chapter discusses spontaneously occurring renal diseases in laboratory animals. Spontaneously occurring renal diseases are common in laboratory animals. However, the diseases vary with each species examined. The chapter also discusses the importance of knowing the background disease patterns in laboratory animals. Knowing the background diseases in a species or strain of animal will aid an investigator in selecting or avoiding a given species for experiments. Such knowledge is also important to understand the similarities or differences between animal and human renal diseases. In some cases, the renal diseases in animals are identical to a human disease whereas in other cases, the diseases in animals have no human counterpart. An example of a disease occurring in animals but not in humans is the chronic renal disease of rats. All rat strains develop chronic renal disease. The cause is unknown, but it is rat-specific with no counterpart in humans. The renal anatomy, histology, and physiology of laboratory animals and humans are similar but not identical. Laboratory animals have a single renal papilla in contrast to humans where there are several conical regions called pyramids. Like humans, animals have a uniform tan to brown color and a smooth glistening capsular surface of the kidney. The functional unit of the kidney is the nephron and the distal tubule is connected to a system of collecting ducts. The nephrons and collecting ducts arise from different embryological primordial. The glomerulus consists of a tuft of capillaries enclosed within Bowmans capsule. The capillaries are lined by thin endothelium and a thin visceral layer of epithelium.

Renal Papillary Cytoplasmic Granularity and Potassium Depletion Induced by Carbonic Anhydrase Inhibitors in Rats

Renal papillary cytoplasmic granularity (RPCG) induced by carbonic anhydrase inhibitors (CAIs) in rats is characterized by the accumulation of dense secondary lysosomes in epithelial, endothelial, and interstitial cells and may be related to drug-induced potassium depletion. Female Sprague-Dawley rats were given the CAI, acetazolamide, by gavage. Half were supplemented with 1% potassium chloride in the drinking water. Two treated groups were allowed to recover for 1 or 2 mo. Potassium supplementation inhibited RPCG by 80% but produced little amelioration of the mild 13% decrease in serum potassium induced by 200 mg/kg/ day acetazolamide for 28 days. Acetazolamide-induced RPCG is reversible because 1- and 2-mo recovery periods decreased the incidence by 75% and 80%, respectively. The results support the hypothesis that RPCG is related to potassium depletion secondary to carbonic anhydrase inhibition. Because supplementation of potassium chloride had little effect on serum potassium, these data suggest that depletion of renal medullary potassium content is important in the pathogenesis of RPCG as previously suggested by others. Other types of diuretics that produce hypokalemia as a side effect may not deplete medullary potassium since RPCG has not been reported in humans or animals given these drugs.

Leiomyoma of the Iris, Sprague-Dawley Rat

A leiomyoma of the iris was composed of bundles of spindle-shaped cells with abundant myoglial fibres and represents the first observation of this rare tumour in a rat.

The Neoplastic Potential of Liver Tumors Induced by Mixed-Function Oxidase Inducers in the Mouse

Prolonged administration to mice of nongenotoxic mixed-function oxidase (MFO) inducers, typified by the much-studied prototype phenobarbital (11), produces liver growth characterized by an increase in weight and centrilobular hepatocyte hypertrophy and hyperplasia. The cells have abundant eosinophilic cytoplasm due to proliferation of smooth endoplasmic reticulum and enlarged, irregular nuclei. When these nodular structures grow to compress the surrounding hepatocytes and lose their normal lobular architecture, they are, by consensus, adenomas. An increase in the incidence of only these tumors may be seen at the end of long-term studies with MFO inducers. According to Butler (1), the incidences of basophilic adenomas and invasive and metastatic carcinomas are not increased by MFO inducers. He provides evidence that these eosinophilic adenomas are different from those that occur spontaneously or those that are induced by genotoxic carcinogens in mice. They differ histologically, biochemically, in cell culture, and after transplantation into nude mice and usually do not have H-ras mutations on codon 61. They almost never develop into carcinomas that invade and metastasize, yet carcinomas (nodules within nodules) are found in some of these eosinophilic nodules (5). Thus, centrilobular hypertrophy and hyperplasia, a zonal adaptive response pattern (6), may provide a favorable environment for some autonomous growth. There appear to be several mechanisms by which this occurs. Phenobarbital, a nongenotoxic carcinogen (10), induced dose- and time-dependent liver enlargement in C57BL/IOJ mice during a 13-wk study. Although replication of centrilobular hepatocytes occurred only during the first week of study (8), persistent increases of mitogenic growth factors [transforming growth factor a (TGF-a) and hepatocyte growth factor (HGF)] and their receptors (epidermal growth factor receptor and HGF receptor) and decreases in the inhibitor of hepatocyte replication (TGF-131) and its receptor (mannose-6