HGH and T4

Your thyroid gland secretes two hormones that are going to be of primary importance in understanding Thyroid/GH interaction. The first is thyroxine (T4) and the second is triiodothyronine (T3). T3 is frequently considered the physiologically active hormone, and consequently the one on which most athletes and bodybuilders focus their energies on. T4, on the other hand, is converted in peripheral tissue into T3 by the enzymes in the deiodinase group, of which there are three types- the three iodothyronine deiodinase either catalyze the initiation (D1, D2) or termination (D3) of thyroid hormone effects. The majority of the body’s T3 (about 80%) comes from this conversion via the first two types of deiodinase, while conversion to an inactive state is accomplished by the third type.