RADIATION-INDUCED MAMMARY TUMORIGENESIS IN PSEUDOPREGNANT RATS MATED WITH VASECTOMIZED PARTNERS

Pseudopregnancy was induced in Wistar-MS female rats by mating with ma le rats 1 month after vasectomy. Pseudopregnant rats received whole-bo dy irradiation with 2.6 Gy gamma-rays at day 7 of pseudopregnancy and were then implanted with a DES pellet as a tumor promoter. In the cont rol groups, virgin 2.5 month-old rats, and normal pregnant rats at day 7 of pregnancy were also exposed to the same dose of radiation. The i ncidence of mammary tumors in rats irradiated in pseudopregnancy (52.6 %) was significantly higher than that in the irradiated virgin rats (2 0.8%), but was not significantly different from that observed in rats irradiated in normal pregnancy (66.7%). The appearance of the first ma mmary tumor in the rats irradiated in pseudopregnancy occurred 4 month s earlier than that in the normal pregnancy group. The proportion of a denocarcinomas in total tumors was 16.7, 0 and 38.5% in rats irradiate d in pseudopregnancy, virgin and pregnancy groups, respectively. The i ncidence of adenocarcinomas was not significantly different among the three groups. (C) 1997 Elsevier Science Ireland Ltd.