Weber G M, Farrar E S, Tom C K, Grau E G
Department of Zoology, University of Hawaii, Honolulu 96822.
Gen Comp Endocrinol. 1994 Apr;94(1):62-71. doi: 10.1006/gcen.1994.1060.
This study describes changes in the thyroid hormones thyroxine (T4) and triiodothyronine (T3) in the toad Bufo marinus during development from early embryonic stages through metamorphosis. Both the total content and concentrations of T4 and T3 were calculated to assess whether changes in these hormones might derive from changes in body mass or water content rather than from changes in hormone production or metabolism. Three clutches of eggs were collected from ponds during the day following fertilization and raised through metamorphosis. Samples of five or more individuals were collected daily for thyroid hormone measurement and body mass determination. Hormones were measured by radioimmunoassay utilizing miniature Sephadex columns after whole-body extraction. Both T4 and T3 were elevated at gastrulation (1 day after fertilization), but declined to low levels within the first week. This is the first report that thyroid hormones occur in anuran embryos prior to thyroid differentiation. This suggests that thyroid hormones are deposited in the anuran egg during oogenesis in a manner similar to that described for teleost fishes and the domestic hen. Levels of T3 and T4 began to rise at about 2 weeks after fertilization (stage 31; staged according to Limbaugh and Volpe, 1957) and peaked during early metamorphic climax (stage 43). This pattern coincides well with the notion that thyroid hormones are central regulators of metamorphosis in B. marinus as has been shown in other amphibians examined to date. Generally, both total content and concentration of the two hormones varied in parallel. Overall, whereas individual mass and water changes may affect the magnitude of hormone changes, they appear to have little input into their direction.
本研究描述了海蟾蜍（Bufo marinus）从胚胎早期发育到变态发育过程中甲状腺激素甲状腺素（T4）和三碘甲状腺原氨酸（T3）的变化。计算了T4和T3的总量及浓度，以评估这些激素的变化是源于体重或含水量的变化，还是源于激素产生或代谢的变化。在受精后的白天从池塘中收集了三窝卵，并饲养至变态发育完成。每天收集五个或更多个体的样本，用于测量甲状腺激素和测定体重。全身提取后，利用微型葡聚糖凝胶柱通过放射免疫分析法测量激素。在原肠胚形成期（受精后1天），T4和T3均升高，但在第一周内降至低水平。这是关于甲状腺激素在无尾目胚胎甲状腺分化之前就已存在的首次报道。这表明甲状腺激素在卵子发生过程中以类似于硬骨鱼类和家鸡的方式沉积在无尾目卵中。T3和T4水平在受精后约2周（第31阶段；根据Limbaugh和Volpe，1957年分期）开始上升，并在变态初期高潮（第43阶段）达到峰值。这种模式与甲状腺激素是海蟾蜍变态发育的核心调节因子这一观点非常吻合，这一点在迄今研究的其他两栖动物中也已得到证实。一般来说，这两种激素的总量和浓度变化是平行的。总体而言，虽然个体质量和水分变化可能会影响激素变化的幅度，但它们似乎对激素变化的方向影响很小。
