The possible reason for serum 3,3'5'-(reverse) triiodothyronine increase in old people.

I Szabolcs, M Weber, Z Kovács, G Irsy, M Góth, T Halász, G Szilágyi
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Abstract

Healthy subjects aged 70-90 and 20-40 years were investigated for the level of reverse triiodothyronine (rT3). The mean level in 57 old subjects was higher and the triiodothyronine (T3) level lower than in 30 young persons. No negative correlation was observed. A serum T3 elevation caused by liothyronine administration (5-15 micrograms/day for two weeks) was not followed by a change of the mean rT3 level in 12 old subjects. After a single intramuscular thyrotropin (TSH) injection, the rT3 elevation lasted 24h longer in 19 old persons than in the 9 control ones, though the early rT3 response was similar in both groups. Propranolol administration (40 mg t.i.d. for a week) caused a similar rT3 elevation in old persons (n = 18) as in 12 young ones. From the indirect data it is concluded that the serum rT3 elevation in old age is a result of faster peripheral generation and not of increased production in the thyroid gland. The data do not indicate any change of rT3 metabolism. T4-T3 and T4-rT3 conversion are provoked by different enzymes. The elevation of rT3 might be a cause of the observed decrease in peripheral T3 generation in old subjects, acting by an inhibition of the T4-T3 conversion.

老年人血清3,3'5'-(反向)三碘甲状腺原氨酸增加的可能原因。
研究了70 ~ 90岁和20 ~ 40岁健康受试者的逆转录三碘甲状腺原氨酸(rT3)水平。57名老年受试者的平均水平高于30名年轻人,三碘甲状腺原氨酸(T3)水平低于30名年轻人。无负相关。12名老年受试者服用碘甲状腺原氨酸(5-15微克/天,持续两周)引起的血清T3升高没有引起平均rT3水平的变化。单次肌内注射促甲状腺素(TSH)后,19例老年人的rT3升高持续时间比9例对照组长24小时,但两组的早期rT3反应相似。心得安(40 mg,次,一周)在18名老年人中引起的rT3升高与12名年轻人相似。从间接数据可以得出结论,老年人血清rT3升高是外周生成更快的结果,而不是甲状腺生成增加的结果。数据未显示rT3代谢有任何变化。T4-T3和T4-rT3转化是由不同的酶引起的。rT3的升高可能是观察到的老龄受试者外周T3生成减少的原因,其作用是抑制T4-T3转化。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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