Sentence:  The mechanism of action of these drugs has not been completely worked out , but certain of them appear to act by <WSD>reducing</WSD> the oxidised form of iodine before it can iodinate thyroglobulin ( Astwood , 1954 ) . 
Meaning of the word marked with <WSD> tags:  to remove oxygen from a compound, or cause to react with hydrogen or form a hydride, or to undergo an increase in the number of electrons