Postnatal exposure to AhR agonists does not affect breast cancer risk in rats.

2004 NOV 4 - (NewsRx.com & NewsRx.net) -- Postnatal exposure to aryl hydrocarbon receptor (AhR) agonists does not affect the risk of breast cancer in rats.

"There are concerns that early life exposure to organochlorines," including AhR agonists, "may lead to long-term effects and increase the risk of developing breast cancer," toxicologists in Canada explained.

D. Desaulniers and colleagues at Health Canada in Ottawa conducted a study to determine "if postnatal exposure to a mixture of 2,3, 7,8-tetrachlorodibenzodioxin (TCDD)-like chemicals would modulate the development of methylnitrosourea (MNU)-induced mammary tumors."

"Females received by gavage a mixture containing three non-ortho-polychlorinated biphenyls (PCBs), six polychlorinated dibenzodioxins (PCDDS), and seven polychlorinated dibenzofurans (PCDFs), at 1, 5, 10, 15, and 20 d of age," the collaborators said. "The doses were equivalent to 0, 1, 10, 100, or 1000 times the amount ingested through breast milk by a human infant during its first 24 d of life."

"Subgroups of 1000x treated rats and controls were sacrificed at 21 d of age for assessment of mammary gland development, cell death, and proliferation," according to the report. "Mammary tumor development was assessed in MNU (30 mg/kg body weight i.p. at 50 days of age)-induced rats pre-exposed to the mixture (MNU-0, MNU-1, MNU-10, MNU-100, MNU-1000)."

"Rats were sacrificed when their mammary tumors reached 1 cm in diameter, or when the rats reached greater than or equal to32 wk of age," published data indicated. "Mammary-gland whole mounts were analyzed with all palpable and microscopic lesions (n=1,563) ...