Fig 1-10. Effects of iodide on thyroid metabolism. All inhibitory effects of iodide, except in part the inhibition of secretion, are relieved by drugs that inhibit iodide trapping (e.g., perchlorate) or iodide oxidation (e.g., methimazole). All effects are direct inhibitions except the effect on iodide transport which bears on the transcription of Na/I- symporter gene. Three possible mechanisms corrresponding to this paradigm are outlined: generation of O 2 radicals, iodination of target proteins and synthesis of an XI compound. Any of these mechanisms could account for the various steps ascribed to XI inhibition by I – (indicated by slashes).