Endocrine Abstracts

Abundant evidence indicates that the three deiodinases (D1, D2 and D3) function at the pre-receptor level to influence both extracellular and intracellular thyroid hormone levels and hence thyroid hormone action. Indirect evidence supports the concept that a major function of the D1 is to generate T3 for export to plasma whereas the D2 generates T3 primarily for local use. To obtain direct evidence concerning their individual physiological roles we have g...

The prohormone T4 represents the majority of circulating thyroid hormones, whereas 80% of the active hormone T3 is derived from T4 by the actions of the type 1 and type 2 deiodinase enzymes (D1 and D2). Local generation of T3 by D2 regulates ligand supply to the nuclear T3-receptor in pituitary, brown adipose tissue and brain, and this enzyme is also expressed in bone. Hypothyroidism in children causes delayed bone age and growth retardation, whereas thyrotoxicosis in adults c...