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Kimura, Ikeda
Lack of effect of soy isoflavone on thyroid hyperplasia in rats receiving an iodine-deficient diet.Son HY, Nishikawa A, Ikeda T, Imazawa T, Kimura S, Hirose M. Jpn J Cancer Res. 2001 Feb;92(2):103-8. [abstract only]
"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
T(4) 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."
Dramatic synergism between excess soybean intake and iodine deficiency on the development of rat thyroid hyperplasia.Ikeda T, Nishikawa A, Imazawa T, Kimura S, Hirose M. Carcinogenesis. 2000 Apr;21(4):707-13.
"The effects of defatted
soybean and/or iodine-deficient diet feeding were investigated in
female F344 rats. Rats were divided into four groups, each consisting
of 10 animals, and fed basal AIN-93G diet in which the protein was
exchanged for 20% gluten (Group 1), iodine-deficient gluten (Group 2),
20% defatted soybean (Group 3) and iodine-deficient defatted soybean
(Group 4). At week 10, relative thyroid gland weights (mg/100 g body
wt) were significantly (P < 0.01) higher in Groups 2 (15.5 +/- 1.3)
and 4 (81.7 +/- 8.6) than in Group 1 (8.4 +/- 2.0) and pituitary gland
weights (mg/100 g body wt) were significantly (P < 0.01) higher in
Groups 3 (9.1 +/- 0. 6) and 4 (9.7 +/- 1.5) than in Group 1 (6.5 +/-
1.5). Serum biochemical assays revealed thyroxine to be significantly
(P < 0.05) lower in Groups 2 and 4 than in Group 1. On the other hand,
serum thyroid-stimulating hormone (TSH) was significantly (P < 0.01)
higher in Groups 3 and 4 than in Group 1. This was particularly
striking for TSH (ng/ml) at week 10 in Group 4 (126 +/- 11) as
compared with Groups 1 (4.36 +/- 0.30), 2 (4.84 +/- 0.80) and 3 (5. 78
+/- 0.80). Histologically, marked diffuse follicular hyperplasia of
the thyroid was evident in Group 4 rats. Proliferating cell nuclear
antigen labeling indices (%) were significantly higher (P < 0.05) in
Groups 2 (4.8 +/- 2.5) and 4 (13.2 +/- 1.1) than in Group 1 (0.4 +/-
0.5). Ultrastructurally, severe disorganization and disarrangement of
mitochondria were apparent in thyroid follicular cells of Group 4. In
the anterior pituitary, dilated rough surfaced endoplasmic reticulum
and increased secretory granules were remarkable in this group. Our
results thus strongly suggest that dietary defatted soybean
synergistically stimulates the growth of rat thyroid with iodine
deficiency, partly through a pituitary-dependent pathway."
Studies on soybean factors which produced goiter in rats.Suwa J, Koyanagi T, Kimura S. J Nutr Sci Vitaminol (Tokyo). 1979;25(4):309-15. [abstract only]
"The goitrogenicities of various preparations obtained from soybean were studied using rats. Thyroid weight, 131I uptake and the ratio of 131I-monoiodotyrosine to 131I-diiodotyrosine of the gland in rats fed the preparation was measured to determine the activity of these preparations. It was resulted that the group of rats receiving the curd had the most hypertrophied thyroid, the enlargement being equal to that in the group of these receiving soybean in the 8 weeks' feeding experiment. No difference on the content of iodine were found with the various diet preparations. The proteolytic digestion of soybean curd did not eliminate the goitrogenic property, thus, the goitrogen seems not to be a protein or peptide-like substance."
Development of malignant goiter by defatted soybean with iodine-free diet in rats.Kimura S, Suwa J, Ito M, Sato H. Gann. 1976 Oct;67(5):763-5. [abstract only]
"Hyperplastic goiters were observed frequently in female rats of Wistar strain when given defatted soybean under iodine deficiency for 6 to 12 months. The findings in the thyroid were those of malignant tumors in which the features of thyroid carcinomas were seen, accompanied with metastasis in the lungs of some animals. Enlargement of the thyroid was completely inhibited in rats when a small amount of iodine was added to the diet. The role of soybean factor(s) which causes enlargement of the thyroid is discussed in relation to the development of malignant goiter, together with pathological findings in the animals."
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