Plasma thyroxine and triiodothyronine levels in spontaneously metamorphosing Rana catesbeiana tadpoles and in adult anuran amphibia.
Plasma thyroxine and triiodothyronine levels in spontaneously metamorphosing Rana catesbeiana tadpoles and in adult anuran amphibia.
复制标题
自发变态林蛙蝌蚪和成年无尾两栖动物的血浆甲状腺素和三碘甲状腺原氨酸水平。
作者：
E. Regard;A. Taurog;T. Nakashima
我们开发了针对两栖动物血浆中 T4 和 T3 的灵敏且可靠的放射免疫测定法，并使用这些程序测量了自发发育的林蛙蝌蚪在变态不同阶段的血浆 T4 和 T3 水平。在变态前期，T4 和 T3 的循环水平均低于 RIA 程序的检测限（T4 低于 50 ng/100 ml，T3 低于 5 ng/100 ml）。血浆T3和T4在变态前期逐渐升高，在变态高潮开始时，T4和T3水平急剧升高。在变态高潮（第 XXIII 阶段）的中期观察到两种激素的峰值水平。循环 T3 水平达到平均峰值 78 ng/100 mg，比变态前期水平至少高 15 倍。 T4峰值水平为0.5微克/100毫升，比变态前水平增加约10倍。甲状腺激素分泌的激增只持续了几天，在变态高潮的后半期，血浆T4和T3出现了相当快的下降。到高潮后 2 天，水平已下降至峰值的 20% 左右。在蝌蚪发育的各个阶段，血浆中的游离 T4 和 T3 水平遵循与总激素水平相同的一般模式。在成年 R. catesbeiana 中，血浆 T4 和 T3 水平出奇地低。在蟾蜍和林蛙中也观察到类似的低值。变态前蝌蚪和成虫中循环 T4 和 T3 的水平都非常低，这表明甲状腺激素在无尾两栖类中可能仅在变态期间才重要。
We have developed sensitive and reliable radioimmunoassays for T4 and T3 in amphibian plasma and have used these procedures to measure plasma T4 and T3 levels in spontaneously developing Rana catesbeiana tadpoles at various stages of metamorphosis. During premetamorphosis circulating levels of both T4 and T3 were below the limits of detection of the RIA procedures (T4 less than 50 ng/100 ml, T3 less than 5 ng/100 ml). A gradual rise in plasma T3 and T4 became apparent during prometamorphosis, and at the onset of metamorphic climax the levels of both T4 and T3 increased sharply. Peak levels for both hormones were observed in the middle of metamorphic climax (stage XXIII). The circulating T3 level reached a mean peak of 78 ng/100 mg, at least 15 times greater than the level during premetamorphosis. The peak T4 level was 0.5 microgram/100 ml, about a 10-fold increase over the premetamorphosis level. The surge in thyroid hormone secretion lasted only for several days, and during the latter half of metamorphic climax there was a fairly rapid decrease in plasma T4 and T3. By 2 days post-climax the levels had declined to about 20% of their peak values. Free T4 and T3 levels in plasma followed the same general pattern as the total hormone levels during the various stages of tadpole development. In adult R. catesbeiana, plasma T4 and T3 levels were surprisingly low. Similarly low values were observed in Bufo marinus and in Rana pipiens. The very low levels of circulating T4 and T3 both in premetamorphosis tadpoles and in adults suggest that thyroid hormones in anuran Amphibia may be of importance only during the period of metamorphosis.