Thyrosin is a breakdown product of the thyroid hormones. It can be itself broken down into Norepinephrine.
thyrosin
Im afraid that your question is quite unclear. If you are refering to how the thymus turns pre-T Cells into Naieve T-cells, this is not a process mediated by a secretion. Its a process called positive and negative selection (or central tollerance) mediated by surface molecules called MHCs present on thymic cells and Dendritic Cells, which eliminates those cells that either do not react with these MHCs or react too strongly. I hope this answers your question.............