Dawson A, Deeming D C, Dick A C, Sharp P J
Institute of Terrestrial Ecology, Abbots Ripton, Huntingdon, PE17 2LS, United Kingdom.
Gen Comp Endocrinol. 1996 Sep;103(3):308-15. doi: 10.1006/gcen.1996.0126.
Thyroid hormones are of interest in ostriches because, in common with other ratites, ostriches are believed to have evolved through neoteny, a process which, in amphibia, is related to thyroid function. Farmed ostriches show marked differences in growth rates, a problem which also could be related to abnormal thyroid function. In adult farmed ostriches (more than 3 years old), mean plasma thyroxine concentration was 1.8 nmol middle dot liter-1 (range 0.2 to 6.5 nmol middle dot liter-1). This is a lower mean and a much greater range than those in adult starlings or Japanese quail measured at the same time. No sex differences were observed. In 5-month-old ostriches (approximately half grown) mean levels were again low (3.1 nmol x liter-1, range 0.2 to 9.9 nmol x liter-1). There was a correlation (P < 0.0005) between thyroxine and body weight, which ranged from 10.8 to 51.5 kg. Growth hormone in this group ranged from 0.7 to 45.6 microg x liter-1, but there was no correlation with body weight or with thyroxine. In the same group of birds at 10 months of age, plasma thyroxine concentrations were similar, but were not correlated with body weight. In young birds sampled between hatch and 13 weeks, mean thyroxine decreased from 7.6 nmol x liter-1 soon after hatching to less than 2 nmol x liter-1 at 2 weeks and remained less than 2 nmol x liter-1 for the following 3 months. Thyroxine was highly variable within and between individuals. There was no correlation with body weight or growth rate. There were no significant differences between values at 13 weeks, 5 months, 10 months, or in adults. The results do not suggest that slow growth is directly related to low thyroxine. However, the low means and wide range of values do suggest that thyroid function in the ostrich is abnormal compared to other birds.
甲状腺激素在鸵鸟研究中颇受关注，因为与其他平胸鸟类一样，鸵鸟被认为是通过幼态持续进化而来的，在两栖动物中，这一过程与甲状腺功能相关。养殖鸵鸟的生长速度存在显著差异，这个问题也可能与甲状腺功能异常有关。在成年养殖鸵鸟（3岁以上）中，血浆甲状腺素平均浓度为1.8纳摩尔·升⁻¹（范围为0.2至6.5纳摩尔·升⁻¹）。这一平均浓度低于同时测量的成年椋鸟或日本鹌鹑，且范围更广。未观察到性别差异。在5个月大的鸵鸟（约半成年）中，平均水平同样较低（3.1纳摩尔·升⁻¹，范围为0.2至9.9纳摩尔·升⁻¹）。甲状腺素与体重之间存在相关性（P < 0.0005），体重范围为10.8至51.5千克。该组中生长激素范围为0.7至45.6微克·升⁻¹，但与体重或甲状腺素均无相关性。在同一组10月龄的鸟类中，血浆甲状腺素浓度相似，但与体重无相关性。在孵化至13周之间采样的幼鸟中，甲状腺素平均浓度在孵化后不久从7.6纳摩尔·升⁻¹降至2周时的不足2纳摩尔·升⁻¹，并在接下来的3个月内一直低于2纳摩尔·升⁻¹。甲状腺素在个体内部和个体之间变化很大。与体重或生长速度均无相关性。13周、5个月、10个月时的值或成年时的值之间无显著差异。结果并不表明生长缓慢与甲状腺素水平低直接相关。然而，较低的平均值和较大的值范围确实表明，与其他鸟类相比，鸵鸟的甲状腺功能异常。
