Abstract
Abstract
Our objective was to determine whether melatonin influenced mammary growth in response to mammogenic hormones. Prepubertal female BALB/c mice were injected for 9 days with 1 μg of 17β-estradiol and 1 mg of progesterone or 17β-estradiol/ progesterone plus 50, 100, or 200 μg of melatonin. Area of the parenchyma and total DNA content of the second thoracic gland were similar between controls and melatonin-injected mice. However, μg of DNA/100 mg of mammary tissue were lower in animals treated with 17β-estradiol/progesterone plus 200 μg of melatonin than in controls. Triglyceride content of mammary glands from animals treated with 100 or 200 μg of melatonin/day increased relative to controls. In an in vitro experiment, thoracic mammary glands of 21-day-old mice were cultured for 6 days in a mammogenic milieu of hormones (17β-estradiol/progesterone, aldosterone, bovine prolactin, growth hormone, and insulin) with 0 (control), 10-6, 10-9, or 10-12 M melatonin. Relative to controls, 10-12 M melatonin increased and 10-6 M melatonin decreased mammary DNA and uptake of [methyl-3H]thymidine. We conclude that high doses of melatonin reduce mammary development in normal mice and that some of this effect may be mediated directly at the mammary tissue.
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