Susceptibility of Male WS/Shi Rats to Melamine but not NaHCO₃ or Butylated Hydroxyanisole Promotion of Urinary Bladder Carcinogenesis

Abstract

Our previous data showed that the F344/DuCrj rat strain is sensitive to the promoting activity of sodium Lascorbate in two-stage urinary bladder carcinogenesis, whereas the WS/Shi rat strain is resistant. In the present study, we found that the latter also lack susceptibility to three other urinary bladder promoters of differing type: NaHCO₃, butylated hydroxyanisole, and melamine. Melamine formed urinary calculi, whereas NaHCO₃ and butylated hydroxyanisole did not. NaHCO₃ alone increased urinary pH and sodium ion concentration. Male rats, 6-week-old, were given 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine in their drinking water for 4 weeks, and then fed basal diet supplemented with 3% NaHCO₃, 2% butylated hydroxyanisole, or 3% melamine for 32 weeks. Melamine, which gives rise to urinary calculi, promoted urinary bladder carcinogenesis, whereas NaHCO₃ did not, despite significant elevation of urinary pH and sodium ion concentration. Butylated hydroxyanisole was also without effect. The results indicate that WS/Shi rats are sensitive to the promotion of two-stage urinary bladder carcinogenesis by melamine, but not NaHCO₃ or butylated hydroxyanisole.