| Project/Area Number |
17591361
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General surgery
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| Research Institution | Kansai Medical University |
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Principal Investigator |
TSUBURA Airo Kansai Medical University, Faculty of Medicine, Professor, 医学部, 教授 (90098137)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUOKA Yoichiro Kansai Medical University, Faculty of Medicine, Associate Professor, 医学部, 助教授 (60219409)
UEHARA Norihisa Kansai Medical University, Faculty of Medicine, Instructor, 医学部, 助手 (30368211)
TAKASHI Yuri Kansai Medical University, Faculty of Medicine, Assistant Professor, 医学部, 講師 (50330212)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2006: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2005: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Keywords | Pregnancy / Estrogen / Progesterone / Rat / N-methyl-N-nitrosourea / Mammary / Cancer / Duration / MNU / Lewis rat / Carcinoma / estrogen / progesterone |
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| Research Abstract |
Early age at first full-term pregnancy inversely correlates with breast cancer risk. The protective effects of pregnancy against mammary cancer can be mimicked in the rat by short-term treatment (21 days or slightly longer) with estrogen and progesterone. However, there have been no precise evaluations of the effects of different durations of exposure to pregnancy levels of estrogen and progesterone on mammary carcinogenesis risk. Female Lewis rats were administered a single intraperitoneal injection of 50 mg/kg MNU at 28 days of age, and then were either left hormone-untreated (control group), or underwent subcutaneous implantation of a 21-day release pellet containing 0.5 mg 17 β-estradiol and 32.5 mg progesterone (E/P pellet) at 42 days of age. The pellet was either replaced every 3 to 4 weeks throughout the experimental period (long-term E/P group), or was implanted only once (short-term group). The rat were sacrificed when they developed a mammary tumor with a diameter of 【greater than or equal】 1cm, or when they reached the age of 29 weeks. In rats implanted with a single E/P pellet, circulating 17β -estradiol and progesterone reached pregnancy levels 2 weeks after implantation, but returned to control levels 8 weeks after implantation. Rats that received long-or short-term E/P treatment had a decreased incidence of mammary carcinoma with a diameter of 【greater than or equal】 1 cm, compared to control rats. However, when histologically detected microcarcinomas (diameter <1 cm) were included for comparison, the E/P-treated groups exhibited an abrupt increase in the number of microcarcinomas from 22 to 25 weeks after MNU injection. Although short-term E/P treatment significantly suppressed mammary carcinomas of all sizes, long-term E/P treatment had no cancer-suppressing effect. Thus, the duration of E/P treatment is an essential factor for the suppression of mammary carcinogenesis.
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