Strain Differences in Sensitivity to the Promoting Effect of Sodium L‐Ascorbate in a Two‐stage Rat Urinary Bladder Carcinogenesis Model

Rat strain differences in sensitivity to the promoting effect of sodium L‐ascorbate (SA) on the development of urinary bladder tumors were investigated. In experiment 1, WS/Shi (WS), ODS/Shi‐od/od (ODS), and LEW/Crj (LEW) rats were initiated with 0.05%N‐butyl‐N‐(4‐hydroxybutyl)‐nitrosamine (BBN) in their drinking water and subsequently given basal Oriental MF diet (M) with or without a 5% SA supplement. In LEW rats the SA treatment increased the induction of neoplastic lesions in the urinary bladder, whereas WS and ODS animals proved unresponsive to its promoting effects. In experiment 2, WS and F344 rats were maintained on two kinds of commercial basal diets, M and CLEA CA‐1 (C), during administration of SA, since dietary factors can influence promoting effects. Feeding M during the promotion period in F344 rats yielded significantly more neoplastic lesions than feeding C, but in WS rats no such dietary influence was apparent. In experiment 3, strain differences in biosynthesis of α‐2u‐globulin (α(2u)‐g) were assessed because both α(2u)‐g in the urine and administration of sodium salts of organic acids such as SA have been reported to be involved in tumor promotion. Immunohistochemical analysis of renal tubules and Western blotting analysis of urine revealed the presence of α(2u)‐g in all three strains examined. These data suggest that differences in susceptibility to promotion are due to genetic factors rather than dietary factors and the ability to synthesize . α(2u)‐g.