Jack L J, Kahl S, St Germain D L, Capuco A V
United States Department of Agriculture, Livestock and Poultry Sciences Institute, Beltsville, Maryland 20705.
J Endocrinol. 1994 Aug;142(2):205-15. doi: 10.1677/joe.0.1420205.
Thyroxine 5'-deiodinase (5'D) catalyses deiodination of the prohormone thyroxine (T4) to the metabolically active hormone 3,5,3'-tri-iodothyronine (T3). Previously, it has been demonstrated that rat mammary gland expresses a 5'D with enzymatic properties equivalent to those of the type I enzyme (5'D-I) found in rat liver and kidney. Using complementary DNA (cDNA) for rat hepatic 5'D-I, we have examined expression of 5'D-I messenger RNA (mRNA) in liver, and mammary gland from virgin and lactating rats, and in seven other tissues from virgin rats. 5'D-I mRNA could not be detected in mammary gland either by Northern blotting or by the more sensitive technique of reverse transcribing mRNA and then amplifying the cDNA by polymerase chain reaction (RT-PCR). Analysis of the seven tissues from virgin rats by RT-PCR showed 5'D-I amplicons in liver, kidney and thyroid. No amplicons were detected in adrenal gland, cardiac muscle, skeletal muscle or spleen. In addition, the effect of lactation intensity on circulating thyroid hormones, hepatic and mammary gland 5'D activity, and hepatic 5'D-I mRNA levels was examined. A strong inverse relationship was noted between increased lactation intensity (suckling burden) and circulating T4 and T3, hepatic 5'D-I activity and hepatic 5'D-I mRNA levels. Mammary gland 5'D activity was positively correlated to lactation intensity. The data presented strongly suggest that the 5'D activity expressed in lactating mammary gland is encoded by a mRNA different from the 5'D-I message found in rat liver, kidney and thyroid gland, and may help explain the differential regulation of 5'D-I activity in these organs during lactation. In addition, hepatic 5'D-I activity was found to be correlated with the concentration of 5'D-I mRNA, suggesting that regulation is pretranslational. Results are consistent with a previously suggested involvement of 5'D in establishing metabolic adaptations to support lactation.
甲状腺素5'-脱碘酶（5'D）催化前体激素甲状腺素（T4）脱碘生成具有代谢活性的激素3,5,3'-三碘甲状腺原氨酸（T3）。此前已证明，大鼠乳腺表达一种5'D，其酶学特性与大鼠肝脏和肾脏中发现的I型酶（5'D-I）相当。利用大鼠肝脏5'D-I的互补DNA（cDNA），我们检测了5'D-I信使核糖核酸（mRNA）在肝脏、未孕和泌乳大鼠的乳腺以及未孕大鼠的其他七种组织中的表达情况。通过Northern印迹法或更灵敏的逆转录mRNA然后用聚合酶链反应（RT-PCR）扩增cDNA的技术，均未在乳腺中检测到5'D-I mRNA。通过RT-PCR对未孕大鼠的七种组织进行分析，结果显示在肝脏、肾脏和甲状腺中存在5'D-I扩增子。在肾上腺、心肌、骨骼肌或脾脏中未检测到扩增子。此外，还研究了泌乳强度对循环甲状腺激素、肝脏和乳腺5'D活性以及肝脏5'D-I mRNA水平的影响。结果发现，泌乳强度增加（哺乳负担）与循环T4和T3、肝脏5'D-I活性以及肝脏5'D-I mRNA水平之间存在强烈的负相关关系。乳腺5'D活性与泌乳强度呈正相关。所呈现的数据有力地表明，泌乳乳腺中表达的5'D活性由一种不同于大鼠肝脏、肾脏和甲状腺中发现的5'D-I信使的mRNA编码，这可能有助于解释泌乳期间这些器官中5'D-I活性的差异调节。此外，发现肝脏5'D-I活性与5'D-I mRNA浓度相关，表明调节发生在翻译前。这些结果与之前提出的5'D参与建立支持泌乳的代谢适应性的观点一致。
