Measurement and regulation of thyroidal status in teleost fish

We have reviewed the stages in teleost thyroid function and its regulation, from the initial biosynthesis of the TH to their eventual interaction with putative receptors

J. G. Eales; S. B. Brown

2004

Scholarcy highlights

  • TH biosynthesis depends on an adequate plasma iodide level, determined partly by dietary iodide and partly by active branchial iodide uptake from the water, Pulse-injected radioiodide can be used to evaluate thyroidal iodide uptake, aspects of TH biosynthesis and TH thyroidal secretion
  • Owing to variable plasma iodide levels, care is required in interpretating these parameters
  • T3 production is inhibited by a moderate T3 excess indicating an autoregulatory system, whereby tissue T3 levels are maintained at a set-point appropriate for a particular physiologic state
  • Less satisfactory but meaningful indices of T3 availability to receptor sites may be obtained from the plasma T3 level and from the tissue T3 level. The former is appropriate if the cell type in question obtains its T3 primarily from plasma; the latter should be measured if the cell type derives its T3 mainly through intracellular deiodinase activity
  • Primary control is mainly central through the hypothalamic-pituitary axis, which regulates thyroidal secretion of T4 and significant amounts of T3

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