The influence of equol on the hypothalamic-pituitary-thyroid axis and hepatic lipid metabolic parameters in adult male rats.
OBJECTIVE
Equol, the principal active metabolite of soy-derived phytoestrogen daidzein, has well-known estrogenic actions. Results of several studies indicate that equol may also have anti-androgenic activities. However, mechanisms of action of equol on hypothalamic-pituitary-thyroid axis (HPTA) and hepatic lipid metabolism in adult male rats have not been determined yet.


METHODS
Equol at two doses of 100 and 250mg/kgbodyweight(BW)/day was orally gavaged for 5days to groups of 4-month-old male rats. As a positive anti-androgenic control group, animals received 100mg of pure anti-androgenic drug flutamide/kgBW/day. Circulating concentrations of thyroid hormones and lipids, and expression levels of genes underlying HPTA function were determined by radioimmunoassay and TaqMan® real-time reverse transcription polymerase chain reaction, respectively.


RESULTS
Flutamide significantly decreased relative prostate weight, whereas equol did not. Both equol and flutamide caused a significant increase in relative liver weights, and decreases in plasma levels of total tetraiodothyronine (T4) and triiodothyronine (T3), whereas free T4 and T3 concentrations were not reduced. Equol caused the marked down-regulation of hypothalamic thyrotropin-releasing hormone mRNA expression, whereas flutamide did not. Equol as well as flutamide significantly down-regulated the expression levels of pituitary thyrotropin beta-subunit mRNA, without altering thyrotropin secretion. Equol caused reductions in plasma levels of total cholesterol, high- and low-density lipoproteins and triglycerides, whereas flutamide exerted opposite effects.


CONCLUSIONS
This is the first study to reveal that in male rats equol did not affect HPTA function and liver lipid metabolism through the anti-androgenic pathway, however, the intrinsic estrogenic actions of equol were observed.
Department of Biology Faculty of Science, Mahasarakham University, Khamriang Sub-district, Kantharawichai District, Mahasarakham Province 44150 Thailand. Electronic address: panida.l@msu.ac.th.
Panida
P
Loutchanwoot
Department of Biology Faculty of Science, Mahasarakham University, Khamriang Sub-district, Kantharawichai District, Mahasarakham Province 44150 Thailand.
Prayook
P
Srivilai
Department of Endocrinology, University Medical Center Göttingen, Robert-Koch-Strasse 40, D-37075 Göttingen, Germany.
Hubertus
H
Jarry
D000818:Animals; D002784:Cholesterol / Q000097:blood; D004435:Eating; D060754:Equol / Q000494:pharmacology*; D015870:Gene Expression; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D050356:Lipid Metabolism / Q000187:drug effects*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology; D017207:Rats, Sprague-Dawley; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood / Q000235:genetics; D013973:Thyrotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D060754:Equol; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin; D002784:Cholesterol; D013974:Thyroxine
Equol; Prostate; Serum lipids; Thyroid hormones; Thyrotropin secretion; Thyrotropin-releasing hormone