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Treatment with the positive control chemical 3 , 3 ' , 5 - triiodo - l - thyronine ( T3 ) significantly decreased whole - body thyroxin ( T4 ) concentrations , increased whole - body T3 concentrations , and upregulated mRNA expression involved in the HPT axis as a compensatory mechanism .
 3 , 3 ' , 5 - triiodo - l - thyronine, thyroxin ( T4 )
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 3 , 3 ' , 5 - triiodo - l - thyronine, thyroxin ( T4 )