OUDE Hypoforum

*suze* schreef:Beste Zazoo,

Hoeveel T's er in je lichaam zitten, dat is wel bekend.
Daar is allemaal onderzoek naar gedaan, kijk eens in http://www.thyroidmanager.org/Chapter6/6-frame.htm in figuur 6-3.

Jan schreef:Hai Louise,

Wat je mogelijk over het hoofd ziet, dat is dat ook een gezonde schildklier maar een klein deel levert van alle door het lichaam benodigde T3.
Alle andere T3 die in het bloed circuleert, die is afkomstig van omzetting van T4 naar T3 in diverse organen en weefsels, zoals onder andere in de lever. Deze omzetting van T4 naar T3 vind ook plaats wanneer alleen T4 aangeleverd wordt door levothyroxine-medicatie. De discussie is dan vervolgens of deze omzetting van T4 naar T3 voldoende is om een optimale T3-voorziening te leveren. Hierover zijn de meningen verdeeld, net zoals ook de ervaringen met het bijslikken van T3 verdeeld zijn.

Kiek schreef:Het is zeer waarschijnlijk dat het grootste deel van de T3 in bloed afkomstig is uit de spieren.

The view that D1 in liver and kidney is largely responsible for plasma T3 production and that D2 is responsible for local T3 production in tissues such as brain has been changed by recent findings that D2 is also expressed in human thyroid and skeletal muscle

The relative roles of the types 1 and 2 iodothyronine deiodinases (D1 and D2) in extrathyroidal 3,5,3′-triiodothyronine (T3) production in humans are unknown. We calculated the rate of thyroxine (T4) to T3 conversion by intact cells transiently expressing D1 or D2 at low (2 pM), normal (20 pM), and high (200 pM) free T4 concentrations. Deiodinase activities were then assayed in cell sonicates. The ratio of T3 production in cell sonicates (catalytic efficiency) was multiplied by the tissue activities reported in human liver (D1) and skeletal muscle (D2). From these calculations, we predict that in euthyroid humans, D2-generated T3 is 29 nmol/d, while that of D1-generated T3 is 15 nmol/d, from these major deiodinase-expressing tissues. The total estimated extrathyroidal T3 production, 44 nmol/d, is in close agreement with the 40 nmol T3/d based on previous kinetic studies. D2-generated T3 production accounts for approximately 71% of the peripheral T3 production in hypothyroidism, but D1 for approximately 67% in thyrotoxic patients. We also show that the intracellular D2-generated T3 has a greater effect on T3-dependent gene transcription than that from D1, which indicates that generation of nuclear T3 is an intrinsic property of the D2 protein. We suggest that impairment of D2-generated T3 is the major cause of the reduced T3 production in the euthyroid sick syndrome.