Darras V M, Kotanen S P, Geris K L, Berghman L R, Kühn E R
Laboratory of Comparative Endocrinology, Zoological Institute, K.U. Leuven, Louvain, Belgium.
Gen Comp Endocrinol. 1996 Nov;104(2):203-12. doi: 10.1006/gcen.1996.0163.
Embryonic chickens (Day 18 of incubation) and 8-day-old posthatch chicks were subjected to an acute glucocorticoid challenge by a single iv injection of corticosterone (B), dexamethasone, or porcine adrenocorticotropin. Plasma samples were analyzed for changes in T4, T3, rT3, alpha-subunit, LH, GH, and B levels; iodothyronine deiodinase activity was measured in liver, kidney, and hypothalamus at several time points after injection. The effects of the different treatments were broadly similar within one age group, but differed clearly between pre- and post-hatch animals. In 18-day-old embryos glucocorticoids increased plasma T3 and decreased plasma T4, rT3, and the calculated TSH index, within hours after injection. These changes were accompanied by an immediate (1-4-24 hr after injection) decrease in hepatic inner ring deiodinating type III enzyme (IRD-III) activity and a delayed (24-48 hr after injection) increase in hepatic outer ring deiodinating type I enzyme (ORD-1) activity. Glucocorticoid challenge in 8-day-old chicks similarly decreased plasma T4 and the TSH index but tended to also lower plasma T3. Hepatic ORD-I activity decreased within 1 hr after injection, while the already very low hepatic IRD-III activity was for the most part unaffected. Acute increases in glucocorticoids lower thyroidal T4 secretion in both pre- and posthatch chickens but have clearly different effects on peripheral thyroid hormone deiodination and hence on circulating T3 at both developmental stages.
对胚胎鸡（孵化第18天）和孵化后8日龄的雏鸡通过单次静脉注射皮质酮（B）、地塞米松或猪促肾上腺皮质激素进行急性糖皮质激素刺激。分析血浆样本中甲状腺素（T4）、三碘甲状腺原氨酸（T3）、反三碘甲状腺原氨酸（rT3）、α亚基、促黄体生成素（LH）、生长激素（GH）和皮质酮（B）水平的变化；在注射后的几个时间点测量肝脏、肾脏和下丘脑的碘甲状腺原氨酸脱碘酶活性。不同处理的效果在同一年龄组内大致相似，但在孵化前和孵化后的动物之间有明显差异。在18日龄胚胎中，注射糖皮质激素后数小时内，血浆T3升高，血浆T4、rT3和计算出的促甲状腺激素（TSH）指数降低。这些变化伴随着肝脏内环脱碘III型酶（IRD-III）活性立即（注射后1-4-24小时）下降，以及肝脏外环脱碘I型酶（ORD-1）活性延迟（注射后24-48小时）升高。对8日龄雏鸡进行糖皮质激素刺激同样降低了血浆T4和TSH指数，但也倾向于降低血浆T3。注射后1小时内肝脏ORD-I活性下降，而原本就很低的肝脏IRD-III活性在很大程度上未受影响。糖皮质激素的急性增加降低了孵化前和孵化后鸡的甲状腺T4分泌，但在两个发育阶段对周围甲状腺激素脱碘以及因此对循环T3有明显不同的影响。
