Amelioration of sodium barbital- induced nephropathy and regenerative tubular hayperplasia after a single injection of streptoxotocin does not abolish the renal tumor promoting effect of barbital sodium in male F344/NCr rats

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Abstract
The renal tumor promoting activity of barbital sodium (BBNa) and the role of renal tubular cell hyperplasia in tumor promotion following initiation with streptoxotocin (STZ) was investigated. Six week old male F344/ NCr rats were given STZ as a single i.p. injection of 50mg/kg body wt and beginning 2 weeks later were fed diets containing 0 or 4000 p.p.m. of BBNA until they were killed at 33, 52 or 72 experimental weeks for histological evaluation and determination of levels of renal DNA synthesis by bromodeoxyuridine (Brdu) Immunohistochemistry. A promoting effect on renal carcinogenesis was found by 72 weeks, but not at 33 or 52 weeks, confirming tha tprolonged administration of BBNa is necessary to promote renal tubular cell neoplasms. The promoting effect was evident as a higher incidence of large renal tubular tumors after 52 weeks, rather than an increase in number of dysplastic tubules, putative preneoplastic lesions. These findings suggest that the targets for the promoting activity of BBNa may be dysplastic lesions which may progress to tumors. Detailed exmination by the step section technique through the entire kidneys revealed that STZ or BBNa administration induced a high incidence of putative preneoplastic renal tubular lesions (dysplasias) which seemed to be derived from the P1 or P2 segment of the nephron, also a site of high Brdu labeling index (LI) associated with BBNa toxicity. STZ administration was also associtaed with attenuation ofBBNa-induced nephropathy and with diabetes from pancreatic islet degeneration and atrophy. The reduction in severity of nephropathy was correlated with a ruduction in the LI of the renal cortical and medullary tubules, but not with the renal tumor incidence. These results indicate that decreased DNA synthesis in target cells does not eliminate tumor promoting activity in renal tubular epithelium. In addition, BBNa alone induced papillomas of the transitional epithelium of the renal pelvis and renal tubular cell adenomas.

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