Eales J G, Morin P P, Tsang P, Hara T J
Department of Zoology, University of Manitoba, Winnipeg, Canada.
Gen Comp Endocrinol. 1993 May;90(2):157-67. doi: 10.1006/gcen.1993.1070.
Outer-ring deiodinase (ORD) and inner-ring deiodinase (IRD) pathways for 3,5,3'-triiodo-L-thyronine (T3) and 3,3',5'-T3 (reverse T3, rT3) were examined in microsomal fractions of liver, heart, gill, brain, and skeletal muscle of 20-month-old Atlantic salmon induced to undergo parr-smolt transformation (PST) in late February and March by imposing a 16-hr photoperiod. All tissues showed negligible T3ORD activity. T3IRD activity was detected in both the liver (Km = 0.65 nM; Vmax = 15.5 pmol T3 deiodinated.hr-1.mg microsomal protein-1) and brain of smolts, but not in gill, heart, or skeletal muscle. rT3ORD was detected in liver, brain, and muscle, and at very low levels in gill and heart. rT3IRD activity occurred to some extent in all tissues except brain. T3IRD activity changed in brain during PST, and was low in brain and liver of post-smolts examined in late October. We conclude that (i) deiodination of T3 proceeds exclusively through an IRD pathway, which may permit regulation of T3 degradation independently of the ORD pathway responsible for T3 formation; (ii) deiodination of rT3 proceeds mainly through an ORD pathway but rT3IRD activity does occur in some tissues; and (iii) the altered brain T3IRD activity during PST suggests regulation of T3 turnover in the brain at this time.
通过设置16小时光照周期，于2月下旬和3月诱导20月龄大西洋鲑进行幼鲑-稚鲑转化（PST），并检测了其肝脏、心脏、鳃、脑和骨骼肌微粒体部分中3,5,3'-三碘-L-甲状腺原氨酸（T3）和3,3',5'-T3（反式T3，rT3）的外环脱碘酶（ORD）和内环脱碘酶（IRD）途径。所有组织的T3 ORD活性均微乎其微。在稚鲑的肝脏（Km = 0.65 nM；Vmax = 15.5 pmol T3脱碘·小时-1·毫克微粒体蛋白-1）和脑中均检测到T3 IRD活性，但在鳃、心脏或骨骼肌中未检测到。在肝脏、脑和肌肉中检测到rT3 ORD，在鳃和心脏中的水平极低。除脑外，rT3 IRD活性在所有组织中均有一定程度的发生。在PST期间，脑中的T3 IRD活性发生变化，在10月下旬检查的稚鲑后阶段，脑和肝脏中的该活性较低。我们得出以下结论：（i）T3的脱碘仅通过IRD途径进行，这可能允许独立于负责T3形成的ORD途径来调节T3的降解；（ii）rT3的脱碘主要通过ORD途径进行，但rT3 IRD活性确实在某些组织中存在；（iii）PST期间脑T3 IRD活性的改变表明此时脑中T3周转受到调节。
