title: Induction of mammary carcinomas by the direct application of crystalline N-methyl-N-nitrosourea onto rat mammary gland.
abstract: The effectiveness of the direct application of crystalline N-methyl-N-nitrosourea (MNU) onto the mammary gland was compared with the systemic intraperitoneal (i.p.) administration method for the induction of mammary carcinomas in female Sprague-Dawley (S-D) rats. The effectiveness was also tested in genetically resistant female Copenhagen (Cop) rats. The 10 mg crystalline MNU was dusted directly onto the right-inguinal mammary gland, or 50 mg/kg body weight MNU solution was given i.p. at 50 days of age. Animals were palpated for tumor detection twice weekly and killed when the tumor reached 1-2 cm in diameter or were necropsied 30 weeks after carcinogen treatment. In S-D rats, all of the 78 tumors produced by dusting were adenocarcinomas. By contrast, 40 tumors produced i.p. were adenocarcinomas, 1 was fibroadenoma, and 5 were lactating adenomas. The cumulative incidence of mammary carcinoma was high in the dusting and the i.p. groups (12/12; 100% and 11/13; 84%, respectively). However, the dusting groups showed a high number of carcinoma per rats (6.5 vs. 3.6; P < 0.01) and short cancer latency (13.8 weeks v.s. 28.1 weeks; P < 0.001) than the i.p. groups. In Cop rats, although low (4/11; 36%), adenocarcinomas were developed by the dusting method. In both strains, adenocarcinomas displayed various degrees of differentiation but no evidence was found for metastasis. For MNU-administration, the direct dusting technique is an effective method and offers added advantages of ease for the induction of mammary carcinomas in rats.
authors.affiliation: Department of Pathology, Kansai Medical University, Osaka, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Takahashi
authors.forename: Y
authors.initials: Y
authors.lastname: Uemura
authors.forename: I
authors.initials: I
authors.lastname: Nakao
authors.forename: A
authors.initials: A
authors.lastname: Tsubura
mesh_terms: D000230:Adenocarcinoma / Q000139:chemically induced* / Q000473:pathology; D000818:Animals; D003460:Crystallization; D005260:Female; D007150:Immunohistochemistry; D007274:Injections, Intraperitoneal; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced* / Q000473:pathology; D008770:Methylnitrosourea / Q000008:administration & dosage* / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D008770:Methylnitrosourea