[Twenty-eight day repeated dose toxicity testing of diphenylamine in F344 rats]

A twenty-eight day repeated dose toxicity test of diphenylamine (DPA) was carried out in male and female F344 rats at dose levels of 1000, 333, 111 or 0 mg/kg/day. Thirty-six animals of both sexes were divided into 6 groups of equal number, 4 groups being used for the 28 days dosing study and the remainder for investigation of recovery. Inhibition of body weight gain, increase of liver, spleen and kidney weights, and anemia were observed in the highest dose groups in both sexes. The same groups demonstrated mucosal hyperplasia in the forestomach, dilatation, degeneration or necrosis of renal tubules in the corticomedullary junction, and hyperplasia in the bone marrow histopathologically. Slight increase of spleen, liver and kidney weights as well as slight degeneration of renal tubules were evident in several animals receiving the dose level of 333 mg/kg/day. Repair of histopathological lesions and anemia occurred within 14-day resting period. Based on these findings, under the present experimental conditions, the no observable effect level of DPA was 111 mg/kg/day.