Abstract：
:Reverse-phase HPLC employing five different solvent systems was used to determine the 125I-labeled products formed in rainbow trout by in vitro incubation at 12 degrees of the hepatic microsome fraction with L-thyroxine (T4) labeled with 125I in the outer phenyl ring. Trout were starved for 2 weeks or fed a 2% ration. The only labeled products identified during incubation for 7.5-70 min over a T4 substrate range of 0.03-0.5 nM were 125I- and 3,5,[125I]3'-triiodo-L-thyronine (T3). These products in combination with the parent [125I]T4 accounted for over 96% of the total chromatographic radioactivity. Neither 3,[125I]3'-diiodo-L-thyronine nor 3,[125I]3',5'-T3 (reverse T3) was detected, suggesting negligible inner-ring deiodination of T4 or T3. Essentially equal production of 125I- and [125I]T3 validated the use of 125I- production as a measure of [125I]T3 generation in assays for hepatic 5'-monodeiodinase activity. However, in some experiments the 125I- level slightly exceeded the [125I]T3 level, indicating that outer-ring deiodination of T3 may occur to a limited degree. In conclusion, the present data for liver support earlier observations from in vivo studies in showing that for trout at 12 degrees deiodination pathways are geared primarily toward T4 outer-ring monodeiodination to produce T3 with undetectable inner-ring deiodination of T3 or T4 and limited outer-ring deiodination of T3.
journal_name
Gen Comp Endocrinoljournal_title
General and comparative endocrinologyauthors
Sweeting RM,Eales JGdoi
10.1016/0016-6480(92)90081-tkeywords:
subject
Has Abstractpub_date
1992-03-01 00:00:00pages
367-75issue
3eissn
0016-6480issn
1095-6840journal_volume
85pub_type
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