Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina, USA.
Mol Reprod Dev. 2010 Sep;77(9):784-94. doi: 10.1002/mrd.21219.
There is increasing evidence that thyroid hormones influence reproduction in vertebrates. However, little information is available on the mechanisms by which this happens. As a first step in determining these mechanisms, we test the hypothesis that the estrogen receptor subtypes (ERalpha, ERbeta-1, and ERbeta-2) are regulated by the thyroid hormone, (T(3)), in the gonads of goldfish. All three subtypes were down-regulated by T(3) in the testis or ovary. We also found evidence that T(3) decreased pituitary gonadotropin expression and decreased transcript for gonadal aromatase. Collectively, it appears that T(3) acts to diminish estrogen signaling by (1) decreasing pituitary LH expression and thus steroidogenesis, (2) down-regulating gonadal aromatase expression and thus decreasing estrogen synthesis from androgens, and (3) decreasing sensitivity to estrogen by down-regulating the ER subtypes. Goldfish are seasonal breeders, spawning once a year, and thus have two distinct periods of growth: somatic and reproductive. Circulating thyroid hormone levels have been found to increase just after spawning. Therefore, we propose that this may be an endocrine mechanism that goldfish use to switch their energy expenditure from reproductive to growth efforts in the goldfish.
越来越多的证据表明，甲状腺激素会影响脊椎动物的繁殖。然而，关于这种情况发生的机制，我们知之甚少。作为确定这些机制的第一步，我们检验了这样一个假设，即雌激素受体亚型（ERalpha、ERbeta-1 和 ERbeta-2）受甲状腺激素（T(3)）在金鱼性腺中的调节。这三种亚型在睾丸或卵巢中均被 T(3)下调。我们还发现证据表明，T(3) 降低了垂体促性腺激素的表达，并降低了性腺芳香酶的转录。总的来说，T(3)似乎通过以下方式减弱雌激素信号：（1）降低垂体 LH 的表达，从而降低类固醇生成；（2）下调性腺芳香酶的表达，从而减少雄激素转化为雌激素的合成；（3）通过下调 ER 亚型降低雌激素的敏感性。金鱼是季节性繁殖者，每年产卵一次，因此有两个明显的生长阶段：躯体生长和生殖生长。循环甲状腺激素水平在产卵后会升高。因此，我们提出这可能是一种内分泌机制，金鱼利用这种机制将其能量消耗从生殖生长切换到生长发育。
