Metabolism of Thyroid Hormone in Liver
The thyroid gland produces predominantly the prohormone thyroxine (T4) together with a small amount of the biologically active hormone 3,3′,5-triiodothyronine (T3). In normal humans and rats 80% of circulating T3 is derived from outer ring deiodination (ORD) of T4 in peripheral tissues. T3 is further degraded by inner ring deiodination (IRD) to 3,3′-T2. T4 and T3 are also metabolized by glucuronide (G) and sulfate (S) conjugation.