Endocrine Abstracts

The type 3 deiodinase enzyme (D3) inactivates T3 and prevents activation of T4 to protect the fetus from premature exposure to thyroid hormones. Rapidly falling levels of D3 activity and rising levels of T3 at birth initiate the onset of cell differentiation and organ maturation during the post-natal period. Congenital hypothyroidism causes delayed ossification with reduced bone mineral deposition and short stature. We hypothesize that increase...

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...

Hypothyroidism causes delayed ossification and growth retardation. T3 stimulates hypertrophic chondrocyte differentiation whereas unliganded T3 receptors (TRs) repress gene expression and maintain cell proliferation in the absence of hormone. During development the type 3 deiodinase enzyme (D3) inactivates thyroid hormones and prevents T3-access to the fetus. At birth diminishing D3 activity and increasing T3 availability triggers the onset of cell differentiation and correlat...