Acta path. microbiol. scand. Sect. A, 86: 333-335, 1978.

BRIEF REPORT UROTHELIAL HYPERPLASIA OF THE URINARY BLADDER OF THE RAT INDUCED BY

MECHANICAL PERFORATION AND PHENACETIN TREATMENT

Sonny Johansson

Department of Pathology 11, University of Goteborg, Sweden

Johansson, S. Urothelial hyperplasia of the urinary bladder of the rat induced by mechanical perforation and phenacetin treatment. Acta path. microbiol. scand. Sect. A, 86: 333-335, 1978.

Mechanical perforation of the urinary bladder of Sprague-Dawley rats and subsequent administration of phenacetin in the diet induced urothelial hyperplasia in I I of 12 rats. No pathological changes were found in the bladders of the control rats only submitted to mechanical perforation or phenacetin treatment only. The hyperplastic changes varied from mild focal urothelial hyperplasia after one week to severe focal and diffuse nodular and papillary hyperplasia after 3 weeks.

Key words Phenacetin; urothelial hyperplasia; mechanical perforation.

Somy Johansson, Department of Pathology 11. Sahlgren's Hospital, 4 I3 45 Goteborg, Sweden.

Accepted as submitted 2.v.78 The association between a heavy intake of phenacetin-

containing analgesics and the development of renal pelvic tumours is well established (Johansson et al. 1974). Primary tumours of the urinary bladder in phenacetin abusers have also been reported ( Johansson & Wahlqvist 1977).

Urothelial hyperplasia of the renal papillae has been induced in rats after long-term treatment with phenacetin (Johansson & Angevall 1976). Hyperplastic changes were also found in a few control rats but there was a significant difference in the degree and severity between the phenacetin-fed rats and the control rats. The hyperplastic changes were associated with vascular changes and/or calcification. In the above study also 2 out of 30 rats developed mild urothelial hyperplasia of the bladder. In a study by Toyoshima & Leighton ( I 975) trauma to the bladder wall, caused by insertion of chalk powder and subsequent formation of bladder calculi, induced papillomatosis and hyperplasia of the bladder mucosa. In their experiment, which lasted for up to 6 weeks, no malignant tumours developed.

This paper is a brief report of a study concerning the combined effects of mechanical trauma and phenacetin on the urinary bladder of the rat.

Material and Methods Experimental design: Twenty male Sprague-Dawley

rats weighing approximately 100 grams, supplied by Anticimex AB, Stockholm, were used. Four of the rats were put on a diet containing 0.535% phenacetin. Sixteen of the rats were anesthetized with phenobarbital; the abdominal cavity was opened and the urinary bladder perforated twice at the dome with a 23 gauge needle. Twelve of these 16 rats were then put on a diet containing 0.535% phenacetin, and 4 rats were given ordinary rat pellets without phenacetin. Four of the ))per- forated(( phenacetin-fed rats, one nnon-perforated(< phe- m t i n fed rats and one control rat were sacrified after one and after 2 weeks. The remaining phenacetin-fed rats (4 + 2) and 2 control rats were sacrificed after 3 weeks. The rats were weighed and the food consumption determined every week throughout the experiment.

Morphological methods: The urinary bladder was inflated with Bouin's solution. The bladder was devided into 2 parts and embedded in methacrylate and parafin. Five pm sections from the paraffin block and one pm sections from the methacrylate block were stained with hematoxylin and eosin and according to Weigert-van Gieson. Histological examination of the kidneys was also performed.

333

Fig. I. Severe urothelial papillary hyperplasia of the urinary bladder of the rat after mechanical perforation and three weeks of phenacetin treatment. H&E x 120.

Results Three out of the 4 ))perforated(( rats showed mild focal

urothelial hyperplasia after one week of eating phenace- tin. Eight rats had diffuse papillary and partly nodular hyperplasia after 2 and 3 weeks of eating phenacetin (Fig. I ) . Urothelial hyperplasia was found in the perforated areas as well as in areas distant from the areas of perforation. In 2 of the rats the entire bladder mucosa was involved. All of the control rats as well as the mon- perforated(( phenacetin-fed rats had a normal bladder mucosa. The renal pelvis and papillae of all rats were of normal appearence.

Comnienrs

Mechanical perforation of the urinary bladder follo- wed by administration of phenacetin in the diet induced urothelial hyperplasia in 1 I / I2 rats after I to 3 weeks of feeding phenacetin. All of the control rats which were only subjected to mechanical perforation or mon-perfo- rated(( phenacetin-fed rats had normal bladder mucosa. These findings indicate that ingestion of phenacetin in combination with mechanical trauma promotes prolife- ration of the urothelium of the bladder in Sprague- Dawley rats. In another study Sprague-Dawley rats were fed for up to I10 weeks the same dose of phenacetin in the diet as in the present study. Only 2 of 30 rats developed mild urothelial hyperplasia of the bladder, one of which also had moderate cystitis (Johansson & Angervall 1976). In 26 of the 30 rats urothelial hyperplasia of the renal papillae was found, often associated with vascular changes and/or calcifica- tion

A concentration of N-hydroxylated phenacetin meta- bolites in the renal papillae of the rat after ingestion of phenacetin has been suggested (Nery I97 I ). Therefore. the localization of the lesions in the renal pelvis and not of the bladder may be caused by a higher concentration of phenacetin or N-hydroxylated metabolites of phenace-

tin in the urothelium of the renal papillae. Also the vascular changes and calcification may provide a locus minoris resistentiae and be of pathogenetic importance for the development of urothelial hyperplasia. equivalent to the trauma to the bladder wall in the present study. The carcinogenic N-hydroxy esters of aromatic amines and amides (phenacetin is an aromatic amide) are highly reactive and shortlived (Miller 1970); therefore a lesser amount of the active substance may be expected to reach the bladder.

It is not possible to determine whether the urothelial hyperplasia of the renal papillae after long-term feeding of phenacetin or the similar changes induced in the bladder after mechanical trauma and phenacetin treat- ment are reactive or preneoplastic. The administration of the nitrofuran N- 4-(-nitro-2-furyl)-2-thiazolyl forma- mide (FANFT) in the diet to rats induces epithelial lesions of the bladder. The lesions progress from mild focal hyperplasia after 2 weeks to microinvasive carcinomas after 25 weeks (Cohen et a / . 1976). If FANFT was discontinued after 6 and 10 weeks. respectively. the hyperplastic changes reverted to normal in the former group and progressed into invasive carcinomas in the latter (Cohen et a / . 1976).

By scanning electron microscopy it has been demon- strated that after 8-1 0 weeks of feeding FANFT there is an appearance of pleomorphic microvilli on the surface of the hyperplastic lesions. These pleomorphic microvilli seemed to indicate irreversibility, i.e. the hyperplastic lesions will not revert to normal but progress into a tumor (Jacobs et al. 1976).

Scanning electron microscopy may be used to determine whether the epithelial lesions induced by mechanical trauma in combination with phenacetin treatment are reactive or preneoplastic Studies of discontinuation of phenacetin after different time- intervals of feeding phenacetin following mechanical trauma would also be necessary.

334

Reserences: Cohen, S . M., Jacobs, J. B., Arai, M., Angervall, L . , Bengtsson. (1. & Wahlqvisr, L.: Cancer 33: Johansson, S. & Friedell. G. H . : Cancer Res. 36: 2508- 743-753, 1974. - Johansson. S . & Wahlqvist. L . : Acta 251 I , 1976. - Jacobs, J. B.. Arai, M., Cohen, S. M. & Path. et Microbiol. Scand.. Sect. A 85: 768-774, 1977. - Friedell, G. H . : Cancer Res. 36: 2512-2517, 1976. - Miller, J.A.:CancerRes.30:559-576, 197O.-Nety. R . : Johansson. S. & Angervall, L.: Acta Path. et Microbiol. Xenobiotica I : 339-343, 1971. - Toyoshinfa, K & Scand., Sect. A 84: 375-383, 1976. - Johansson. S., Leighton, J . : Cancer Res. 35: 3786-3791, 1975.

335