Oberkotter L V
Department of Biological Sciences, Florida Institute of Technology, Melbourne 32901.
Proc Soc Exp Biol Med. 1988 Mar;187(3):360-5. doi: 10.3181/00379727-187-42677.
It has been demonstrated that orally administered thyrotropin (bovine, bTSH) evokes an increase in circulating T4 and T3 levels in 15-day-old suckling rat pups, but not in weaned animals. Because the feedback mechanisms of the hypothalamo-pituitary-thyroid axis change dramatically during the neonatal period, we chose to examine the efficacy of exogenous bTSH in eliciting a thyrostimulatory response via the subcutaneous (sc) or peroral (po) route in rat pups at 5, 8, 12, and 15 days postpartum. Suckling pups were divided into four groups and received one of the following: (i) 2 IU bTSH/100 g body wt administered sc; (ii) distilled H2O (dH2O) sc; (iii) 2 IU bTSH/100 g body wt given po; (iv) dH2O po. Animals were sacrificed at Time 0 and 1, 2, and 3 hr post-treatment, and the collected serum was analyzed for T4 and T3 by RIA. Maximum serum T4 levels were attained at 2-3 hr post-treatment, and the T4 response to sc-bTSH was significantly greater than that of the po-bTSH groups at all ages examined. This difference became progressively greater with increasing age, due to a persistent decline in T4 responsiveness in animals receiving po-bTSH. No significant differences in T4 or T3 levels attained were observed in 8-day-old rat pups treated with rat vs bovine TSH, either sc or po. Percentage T4 response (vs basal levels) steadily declined between Days 5 and 15 postpartum, in both sc- and po-bTSH treatment groups. Percentage T3 responsiveness to sc-bTSH also declined between 5 and 12 days postpartum, after which time T3 generation increased. Our results suggest that the neonatal rat is highly responsive to exogenous TSH late in the first week of life, and that the permeability of the gut at this stage of development further facilitates the impact of orally ingested TSH in the suckling.
已证实，口服促甲状腺素（牛源，bTSH）可使15日龄哺乳大鼠幼崽的循环T4和T3水平升高，但对断奶动物则无此作用。由于下丘脑 - 垂体 - 甲状腺轴的反馈机制在新生儿期会发生显著变化，我们选择研究外源性bTSH经皮下（sc）或口服（po）途径对产后5、8、12和15天大鼠幼崽引发甲状腺刺激反应的效果。哺乳幼崽分为四组，分别接受以下处理之一：（i）2 IU bTSH/100 g体重，皮下注射；（ii）蒸馏水（dH2O），皮下注射；（iii）2 IU bTSH/100 g体重，口服；（iv）dH2O，口服。在处理后0、1、2和3小时处死动物，并通过放射免疫分析（RIA）检测收集的血清中的T4和T3。血清T4最高水平在处理后2 - 3小时达到，并且在所有检测年龄中，皮下注射bTSH组的T4反应显著大于口服bTSH组。随着年龄增长，这种差异逐渐增大，这是由于口服bTSH动物的T4反应持续下降所致。在8日龄大鼠幼崽中，无论是皮下注射还是口服，用大鼠促甲状腺素与牛促甲状腺素处理后，所达到的T4或T3水平均未观察到显著差异。在产后5至15天，皮下注射和口服bTSH处理组的T4反应百分比（相对于基础水平）均稳步下降。皮下注射bTSH的T3反应百分比在产后5至12天也下降，此后T3生成增加。我们的结果表明，新生大鼠在出生后第一周后期对外源性促甲状腺素高度敏感，并且在这个发育阶段肠道的通透性进一步促进了口服摄入的促甲状腺素对哺乳幼崽的影响。
