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Japanese Journal of Cancer Research : Gann logoLink to Japanese Journal of Cancer Research : Gann
. 2001 Feb;92(2):103–108. doi: 10.1111/j.1349-7006.2001.tb01071.x

Lack of Effect of Soy Isoflavone on Thyroid Hyperplasia in Rats Receiving an Iodine‐deficient Diet

Hwa‐Young Son 1,✉, Akiyoshi Nishikawa 1, Takako Ikeda 1,2, Takayoshi Imazawa 1, Shuichi Kimura 2, Masao Hirose 1
PMCID: PMC5926687  PMID: 11223538

Abstract

We have reported a dramatic synergism between soy intake and iodine deficiency regarding induction of thyroid hyperplasia in rats. Because isoflavones are active constituents of soybeans, in the present study, their possible contribution was examined. Female F344 rats were divided into 8 groups, exposed to diet containing a 0.2% soy isoflavone mixture (SI), 0.2% SI+iodine deficiency (ID), 0.04% SI, 0.04% SI+ID, 20% defatted soybean (DS) alone, 20% DS+ID, ID alone or basal diet alone for 5 weeks. Thyroid weight was not influenced by SI, but was increased by the ID and DS diets with a further significant increment in the DS+ID group (P<0.01). Compared to the control value, serum T4 was significantly (P<0.01) increased by 20% DS alone and decreased in all groups given the ID treatment (P<0.001). Serum thyroid stimulating hormone (TSH) level was increased by ID, and further enhanced by DS (P<0.01) but not SI. Histopathologically, diffuse hypertrophy and/or hyperplasia of thyroid follicles were observed in the ID‐treated groups, the severity being enhanced by DS but not SI. Proliferating cell nuclear antigen labeling indices (%) were elevated in the ID diet groups and again enhanced by DS, but not SI. These results thus suggest that isoflavones may not be involved in the mechanisms underlying the synergistic goitrogenic effect of soybean with iodine deficiency.

Keywords: Thyroid, Isoflavone, Iodine‐deficient, Soybean

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