Neoplasia induced in male rats fed lead acetate, ethyl urea, and sodium nitrite

Sprague-Dawley rats were exposed to 0, 26, or 2600 ppm lead as lead acetate in drinking water for 76 weeks. At 28 weeks of lead exposure, a portion of each group was exposed simultaneously to 6.36 g/kg ethyl urea (EU) and 2.0 g/kg sodium nitrite (NaNO2) for a duration of 20 weeks, and then continued an additional 28 weeks on standard diet free of EU and NaNO2. The animals were observed for incidence, latency, and distribution of tumors. Rats exposed to 2600 ppm lead alone had 81% renal tumors, while rats given 2600 ppm lead in combination with EU/NaNO2 had a 50% incidence. Renal tumors did not occur in the EU/NaNO2 only or EU/NaNO2-26 ppm lead groups. The major tumor type found in EU/NaNO2-exposed rats was lymphosarcoma. Lead did not appear to be syncarcinogenic to the activity of ethylnitrosourea, the carcinogen formed by oral exposure to EU and NaNO2. The lead-induced renal neoplasms were histologically similar to those which occur spontaneously in man and, therefore, may serve as an animal model to study human disease.