In recent years, it has been emphasized that the changes which are a con- sequence of bacterial infection of the kidney may also result from other types.
L R LAWRENCE R. FREEDMAN*
C R F E A
of Department Yale University
Internal Medicine, School of Medicine
EXPERIMENTAL PYELONEPHRITIS. XII. CHANGES MIMICKING CHRONIC PYELONEPHRITIS AS A CONSEQUENCE OF RENAL VASCULAR OCCLUSION IN THE RATt
In recent years, it has been emphasized that the changes which are a consequence of bacterial infection of the kidney may also result from other types of injury.1'2 Nevertheless, in the minds of many, it is still considered possible to distinguish, by tissue changes alone, chronic pyelonephritis produced by bacteria from other nonbacterial renal insults. While studying the relation of renal vascular occlusion to susceptibility to infection in rats, it was noted that it was not possible, histologically, to distinguish infected from noninfected kidneys that had been subjected to a measured interval of anoxemia.8 These studies were conducted about one week after anoxemia and infection, and thus were concerned with acute inflammation. The purpose of the present report is to describe the changes that are seen one to four months after a single interval of occlusion of the main renal artery or vein in the rat. Bacteria were not given to the test animals. MATERIALS AND METHODS
Male Sprague-Dawley rats weighing 200 to 300 gm. were used as experimental animals. Occlusion of the main artery or vein to one kidney was maintained for 1 /2 to 2 hours as described previously.' Following the experimental procedure, the animals were returned to their cages, allowed free access to water and lab chow pellets and were untouched until the kidneys were removed for histological and bacteriological study. Most animals were subjected to 1X'2 hours of vascular occlusion since deaths in the post-operative period were frequent after two hours of vascular occlusion. Histological and bacteriological studies were carried out in the manner reported previously.4 Samples of blood, urine and one half of each kidney were examined bacteriologically. Associate Professor of Medicine. t Supported by Career Development Award No. 6K3-HD-22,587 of the U.S. Public Health Service, National Institute of Child Health and Human Development and by Research Grant No. 4767 from the Institute of Allergy and Infectious Disease, U.S. Public Health Service. Received for publication 15 February 1966. *
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RESULTS
Bacteriological and histological studies were conducted on the kidneys of 27 rats 4 to 16 weeks after a timed period of arterial or venous occlusion. Cultures of one half of each kidney and of the urine and blood at the time of removal of the kidneys were negative, by the techniques used, in all instances. After 45 minutes of arterial or venous occlusion, the changes at 10 to 16 weeks were minimal. The test kidneys were not decreased in size as compared to the opposite control kidney. The histological changes consisted of small scattered foci of tubular atrophy in the cortex surrounded by lymphocytes. Occasional glomeruli were seen in varying stages of atrophy, the changes ranging from thickening and fusion of capillary loops to shrinkage and hyalinization of the entire glomerulus. A few tubules in the outer zone of the medulla were dilated and filled with colloid material. Most of the rats were subjected to renal venous occlusion for 1Y2 hours. In these animals, a definite decrease in size of the test kidney was seen in seven of fourteen animals (Figure 1). In three animals subjected to 1Y2 hours of renal artery occlusion, all test kidneys were small. In the five rats whose renal veins were occluded for two hours, all the test kidneys were decreased in size and to a somewhat greater extent than was found after 1 X2 hours of venous occlusion (Figure 2). In addition to decrease in size of the test kidneys and enlargement of the control kidneys, the changes visible on gross examination included loss of the normal zone distinctions in the test kidneys (Figures 1, 2). After two hours of vascular occlusion, calcification of renal scars and flattening of the papilla was sometimes seen (Figure 2). Vascular lesions indicative of recent or past thrombosis were not encountered in any animals. The histological changes encompassed the same spectrum in kidneys subjected to arterial or venous occlusion and there were no consistent differences between those examined four to sixteen weeks after anoxemia. Varying degrees of fibrosis of tubules and interstitium constituted the basic change observed. The scarring was most prominent in the cortex but involved the medulla and papilla also. Some scars were almost acellular, whereas others contained dense collections of mononuclear cells (Figure 3), in some instances resembling lymphoid follicles. Other noteworthy features included a sharp line of demarcation between scarred and normal cortical tissue (Figure 4). Easily visible were glomerular crowding (Figures 3-5), periglomerular fibrosis (Figure 5) and areas of large zones of castfilled tubules, so called "thyroidization" of the renal tubules (Figure 5). 114
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In rare instances, dilated tubules were seen in the cortex which were filled with cellular casts composed of debris, degenerating nuclei and polymorphonuclear leucocytes. Polymorphonuclear leucocytes were not seen in the interstitium. Thrombosis of vessels was not detected histologically and foci of calcification were seen only in the few kidneys that had been subjected to two hours of vascular occlusion. DISCUSSION
The experiments described in this report were an outgrowth of a chance observation made during a study of the effects of anoxemia on susceptibility of the kidney to infection. It was found previously that the acute changes of anoxemia were the same in infected and noninfected kidneys whose major renal vessels had been occluded for 1 Y2 to 2 hours.8 The present experiments focused on the state of the kidneys 4 to 16 weeks after 1 Y2 to 2 hours of occlusion of the main renal artery or vein. Bacteria were not used and cultures at the time of examination of the animals were sterile. The histological changes in kidneys whose major renal vessels were occluded for a short interval 4 to 16 weeks previously were indistinguishable from the chronic changes known to result from bacterial infection in the kidneys of animals. It is apparent, therefore, that in rats, changes mimicking chronic bacterial pyelonephritis can be produced by anoxemia zwithout bacterial infection. These experimental lesions parallel quite closely what is called chronic pyelonephritis in man. 2' 5 Some features of "typical chronic pyelonephritis" in man are unusual in bacterial pyelonephritis of animals. As had been pointed out previously, although colloid casts may be found in many experimental renal lesions such as hypertensiond or hypertrophy and ageing,' bacterial pyelonephritis in animals rarely results in prominent colloid cast formation leading to "thyroidization" of tubules unless obstruction to urine flow has been produced by stone formation, ureteral ligation or papillary injury.4 In the present experiments, however, colloid cast formation was common. When microscopic slides from the anoxemic kidneys were shown to experienced pathologists, chronic pyelonephritis was invariably the diagnosis made. These observations are pertinent to the problems attending the studies of the pathogenesis of renal disease in man. If these studies in rats indicate that the same kind of lesions can be produced by anoxemia in man, then clinical states where there is anoxemia, e.g., severe vascular disease, 115
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might be accompanied by these lesions in the kidney. In diabetes mellitus or severe hypertension and arteriolosclerosis, one would anticipate that the diagnosis of bacterial chronic pyelonephritis would be difficult. Indeed, this seems to be the case; some experienced observers refuse to consider renal biopsy specimens from diabetics for the presence of chronic pyelonephritis.8 In malignant hypertension, the claim has been made that chronic pyelonephritis is present at autopsy in the vast majority of instances9 but there is considerable disagreement from one report to the next, no doubt a consequence of the nonspecificity of the pathological changes of pyelo-
nephritis.' The discrepancy between the preponderance of clinical urinary tract infections in women and the equal distribution of the diagnosis of chronic pyelonephritis among the sexes at autopsy may also, in part, be explained by the role of vascular disease in the production of these lesions.9"' In a previous study, the finding of hypertensive vascular disease stood out as a theoretical explanation for the high rates of histological chronic pyelonephritis in men.' Other situations in which these experiments may be pertinent include renal transplantation. Some of the lesions encountered after anoxemia alone resemble quite closely the changes noted in immunological rejection reactions. Since anoxemia is an inevitable consequence of transplantation procedures, one can only speculate as to how much this injury contributes to the histological picture of rejection. It is also necessary to consider the possibility that the histological picture of chronic pyelonephritis may be a consequence of vascular injury due to acute bacterial pyelonephritis. Thus, an acute infection could, in hours, temporarily influence blood flow so that the lesions developing over the succeeding months would progress without regard to the ease and rapidity with which the original infection was eliminated. Kincaid-Smith has described acute inflammatory lesions of arteries in acute pyelonephritis and believes that these vascular lesions are responsible for hypertension when they produce the type of pyelonephritic lesion called ischemic tubular atrophy.' It is evident from studies of experimental vascular disease, however, that ischemic tubular atrophy may result from vascular disease without pyelonephritis' and, furthermore, that ischemic atrophy of the cortex may result from bacterial pyelonephritis without detectable organic arterial narrowing.' Whatever the relation between vascular disease, hypertension and pyelonephritis, it is not likely that it will be clarified by a study of morphological changes in the kidney alone, since in animals the lesions 116
....'
..
FI(;. 1. Gross appearance of kidnleys four weeks after occlusioni of the left main renial vein for 1'2 hours. Note the (lecrease in size of the test kidnley, thle gralnularity of its surface and(I the loss of normal distinictioi b)etween cortex ani(l imed(lulla.
METtRC
-23
41
2. . ...........fkile s o r XXck atr oclsol f th et al .I ...........hus.Ca1gs sm la o ths 1 Fgr I n a(ltcll hr o .......lg to appar
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.....................
he rnlpail
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FIG. 3.
FIG. 4
FIG. 5
FIGs. 3, 4, 5. Microscopic views of typical changes evident 4 to 16 weeks after occlusion of the main renal artery or vein for 1 /2 hours. The prominent features are tubular atrophy and dense mononuclear cell tissue infiltration (Fig. 3); sharp line of demarcation between infiltrate and normal cortex and glomerular crowding (Fig. 4); large zone of atrophic tubules filled with colloid casts, glomerular crowding and periglomerilar fibrosis (Fig. 5).
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produced by temporary vascular occlusion, chronic vascular narrowing, and bacterial infection may be indistinguishable. The precise means by which anoxemia brings about the changes found is not clear. Various possibilities exist: direct cell damage and death leading to inflammation or perhaps sufficient cell damage to permit the formation of autoantibodies thus leading to the persistence of immunologically active cells.' Finally, there is the possibility that anoxemia permits the development of virus or bacterial infections not detected by the cultural techniques used in this study.' It is unlikely that the common types of bacterial infection could have resulted from the procedure and healed prior to examination, since no spontaneous infections were detected in cultures taken one week after vascular manipulation.! SUMMARY
Histological lesions, indistinguishable from those of bacterial chronic pyelonephritis, were observed in rats 4 to 16 weeks after total occlusion of the main renal artery or vein for 1 Y2 to 2 hours. Bacteria were not introduced as part of the experimental procedure and could not be found at the time of histological study. These data support the view that it is difficult, if not impossible, to incriminate remote bacterial infection of the kidney as the cause of a specific renal lesion on the basis of morphological criteria alone. REFERENCES
1. Freedman, L. R.: Pyelonephritis and urinary tract infection. In, Diseases of the Kidney, M. B. Strauss and L. G. Welt (Eds.). Boston, Little, Brown, and Co., 1963, pp. 469-500. 2. Pawlowski, J. M., Bloxdorf, J. W., and Kimmelstiel, P.: Chronic pyelonephritis, a morphologic and bacteriologic study. New Engl. J. Med., 1963, 268, 965-969. 3. Godley, J. A. and Freedman, L. R.: Experimental pyelonephritis. XI. A comparison of temporary occlusion of renal artery and vein on susceptibility of the rat kidney to infection. Yale J. Biol. Med., 1964, 36, 268-278. 4. Freedman, L. R., Werner, A. S., Beck, D., and Paplanus, S.: Experimental pyelonephritis. IX. The bacteriological course and morphological consequences of staphylococcal pyelonephritis in the rat, with consideration of the specificity of the pathological changes observed. Yale J. Biol. Med., 1961, 34, 40-51. 5. Weiss, Soma and Parker, Frederic, Jr.: Pyelonephritis: Its relation to vascular lesions and to arterial hypertension. M!1edicine, 1939, 18, 221-315. 6. Heptinstall, R. H. and Stryker, M.: Experimental pyelonephritis. A study of the susceptibility of the hypertensive kidney to infection in the rat. Bull. Johns Hopk. Hosp., 1962,111, 292-306. 7. Morrison, A. B.: Experimentally induced chronic renal insufficiency in the rat. Lab. Invest., 1962, 11, 321-332. 8. Raaschou, F.: Discussion in: Progress in Pyelonephritis, E. H. Kass (Ed.). Philadelphia, F. A. Davis Co., 1965, p. 374. 117
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9. Saphir, Otto and Cohen, N. A.: Chronic pyelonephritis lenta and the "malignant phase of hypertension." Arch int. Med., 1959, 104, 748-762. 10. Kleeman, S. E. T. and Freedman, L. R.: The finding of chronic pyelonephritis in males and females at autopsy. New Engl. J. Med., 1960, 263, 988992. 11. Freedman, L. R., Phair, J. P., Seki, M., Hamilton, H. B. and Nefzger, M. D.: The epidemiology of urinary tract infections in Hiroshima. Yale J. Biol. Med., 1965, 37, 262-282. 12. Kincaid-Smith, Priscilla: Vascular obstruction in chronic pyelonephritic kidneys and its relation to hypertension. Lancet, 1955, 2, 1263-1269. 13. Heptinstall, R. H., Michaels, L., and Brumfitt, W.: Experimental pyelonephritis: The role of arterial narrowing in the production of the kidney of chronic pyelonephritis. J. Path. Bact., 1960, 80, 249-258. 14. White, F. N. and Grollman, A.: Autoimmune factors associated with infarction of the kidney. Nephron, 1964, 1, 93-102. 15. Pandola, G. A., Kreutner, A., Kreutner, K., and Farmer, S. G.: Experimental ascending pyelonephritis in rats. Experimental hydronephrosis with sterile pyelonephritis. Lab. Invest., 1964, 13, 1484-1489.
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