Pekary A E, Hershman J M, Sugawara M, Gieschen K I, Sogol P B, Reed A W, Pardridge W M, Walfish P G
J Gerontol. 1983 Nov;38(6):653-9. doi: 10.1093/geronj/38.6.653.
In order to identify the changes in thyroid regulation and function that are responsible for the age-related decline in T4 secretion, we measured the secretory response of the rat pituitary and thyroid glands to thyrotropin-releasing hormone (TRH), plasma T1/2 for 125I-rat thyrotropin (TSH), the molecular weight of pituitary TSH, T4 uptake and conversion to T3 by the liver, amount of T4 and T3 in serum and in thyroglobulin, and the thyroid peroxidase concentration. The molecular weight of TSH and the biexponential plasma clearance of TSH were not affected by aging. TSH response to TRH administered intravenously did not differ between old and young rats. T3 response to TRH was greater and T4 response lower in old compared with young rats despite levels of T4 and T3 in thyroglobulin which were not affected by aging. Aging effects on hepatic conversion of T4 to T3 varied between rat strains. T4 uptake by liver in vivo by old rats was the same as that reported for young animals. The data are consistent with a marked decrease in the ratio of T4 to T3 secreted by the aging rat thyroid in both the basal and stimulated state possibly due to increased intrathyroidal conversion of T4 to T3.
为了确定导致与年龄相关的甲状腺素（T4）分泌下降的甲状腺调节和功能变化，我们测量了大鼠垂体和甲状腺对促甲状腺激素释放激素（TRH）的分泌反应、125I-大鼠促甲状腺激素（TSH）的血浆半衰期、垂体TSH的分子量、肝脏对T4的摄取和转化为T3的情况、血清和甲状腺球蛋白中T4和T3的含量以及甲状腺过氧化物酶浓度。TSH的分子量和TSH的双指数血浆清除率不受衰老影响。静脉注射TRH后，老年大鼠和年轻大鼠的TSH反应没有差异。尽管甲状腺球蛋白中的T4和T3水平不受衰老影响，但与年轻大鼠相比，老年大鼠对TRH的T3反应更大，T4反应更低。衰老对肝脏将T4转化为T3的影响因大鼠品系而异。老年大鼠肝脏在体内对T4的摄取与年轻动物的报道相同。这些数据与衰老大鼠甲状腺在基础状态和刺激状态下分泌的T4与T3之比显著降低一致，这可能是由于甲状腺内T4向T3的转化增加所致。
