Suppressive effects of genistein and daidzein on pituitary-thyroid axis in orchidectomized middle-aged rats.
High intake of soybean phytoestrogens, isoflavones genistein (G) and daidzein (D), has been associated with health benefits. However, isoflavones were reported to affect adversely thyroid function in the presence of other goitrogenic factors. As the thyroid gland becomes functionally impaired with age, we examined whether supplementary doses of G or D would affect morphology and function of pituitary-thyroid axis in middle-aged male rats. Sixteen-month-old orchidectomized Wistar rats were treated with 10 mg/kg of either G or D, while the control sham-operated and orchidectomized group received just the vehicle for three weeks. The animals were fed soy-free diet with increased iodine content, and killed 24 h after the last treatment. Their pituitaries and thyroids were excised and prepared for further immunohistochemical and morphometric investigation. The concentrations of thyroid-stimulating hormone (TSH), total T(4) and T(3), in the serum were determined. In both isoflavone-treated groups, pituitary TSH-immunopositive cells had increased cellular volume and relative volume density (P < 0.05), as well as increased serum TSH levels (P < 0.05) in comparison to the controls; their thyroid tissue was characterized by increased volume of thyroglobulin-immunopositive epithelium (P < 0.05), epithelial height and index of activation rate (P < 0.05), while the volume of luminal colloid, and total serum T(4) and T(3) levels decreased (P < 0.05) in comparison to the controls. In conclusion, this study provides the first direct evidence that both G and D can induce microfollicular changes in the thyroid tissue and reduce the level of thyroid hormones in Orx middle-aged male rats, a model of andropause. This reduction consequently led to a feedback stimulation of pituitary TSH cells. The detected stimulatory effect was higher in the daidzein-treated rats.
Sosić-Jurjević
Branka
B
Institute for Biological Research 'Sinisa Stanković', University of Belgrade, Despot Stefan Blvd 142, 11060 Belgrade. brankica@ibiss.bg.ac.rs
Filipović
Branko
B
Ajdzanović
Vladimir
V
Savin
Svetlana
S
Nestorović
Natasa
N
Milosević
Verica
V
Sekulić
Milka
M
D000375:Aging / Q000097:blood / Q000187:drug effects*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D053145:Cell Nucleus Size / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D019833:Genistein / Q000008:administration & dosage / Q000494:pharmacology*; D007279:Injections, Subcutaneous; D007529:Isoflavones / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D009919:Orchiectomy; D009929:Organ Size / Q000187:drug effects; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D052684:Thyrotrophs / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D007529:Isoflavones; D014284:Triiodothyronine; C004742:daidzein; D013972:Thyrotropin; D019833:Genistein; D013974:Thyroxine