• Open Access

Effects of Reproduction on Spontaneous Development of Endometrial Adenocarcinomas and Mammary Tumors in Donryu Rats

Authors

  • Takaharu Nagaoka,

    1. Safety Evaluation, Drug Development Laboratories, Pharmaceutical Research Division, Yoshitomi Pharmaceutical Industries Ltd., 14–1 Yamasaki, Fukusaki-cho, Kanzaki-gun, Hyogo 679–2296
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  • Kiyoshi Takegawa,

    1. Safety Evaluation, Drug Development Laboratories, Pharmaceutical Research Division, Yoshitomi Pharmaceutical Industries Ltd., 14–1 Yamasaki, Fukusaki-cho, Kanzaki-gun, Hyogo 679–2296
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  • Masaki Takeuchi,

    1. Safety Evaluation, Drug Development Laboratories, Pharmaceutical Research Division, Yoshitomi Pharmaceutical Industries Ltd., 14–1 Yamasaki, Fukusaki-cho, Kanzaki-gun, Hyogo 679–2296
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  • Akihiko Maekawa

    Corresponding author
    1. Department of Pathology, Sasaki Institute, 2–2 Kanda-Surugadai, Chiyoda-ku, Tokyo 101–0062
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Abstract

Effects of reproduction on spontaneous development of uterine endometrial adenocarcinomas and mammary tumors in Donryu rats were investigated. While the incidence of endometrial adenocarcinomas in Donryu rats was not influenced by a single reproductive experience (SRE), it showed a tendency to decrease in animals having three reproductive experiences (TRE), compared to the nulliparous case (NRE). In addition, both SRE and TRE animals showed delayed occurrence and decreased incidences and mean numbers of mammary tumors, along with reduced incidences of proliferative lesions in the pituitary gland and mucinous epithelium in the vagina. The appearancetime and incidences of persistent estrus in TRE rats were delayed and low, respectively, compared to the SRE and NRE values. The hormonal environment was altered in both groups, the prolactin level in TRE especially being decreased. These results suggest that suppression of the occurrence of endometrial adenocarcinomas and mammary tumors in rats experiencing reproduction is associated with change in the hormonal milieu.

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