Summary
Excess iodide inhibits several thyroid parameters, by a putative organic iodocompound.
Different iodolipids, including iodinated derivatives of arachidonic acid (IAs), are
produced by rat, calf and pig thyroid. The action of two iodolactones, one bearing
the iodine atom at the position 6 (IL-d) and the other at position 14 (IL-w) on growth
of FRTL-5 cells was studied. KI, IL-w and IL-d exert a dose-related inhibition on
FRTL-5 cell profileration. The first two compounds caused inhibition at 1 μM while
IL-d was effective at 10 μM. This inhibitory action of iodolactones (ILs) was not
altered by 1 mM methyl-mercaptoimidazol (MMI), indicating that they exert their effect
per se. The action of ILw on cell growth was reversible. The growth-stimulating effect
of 10 uM forskolin was inhibited by IAs, showing that one possible site of action
lies at the cAMP pathway. The present results give further support to our hypothesis
about the role of IAs in thyroid growth autoregulation.
Key words
Iodide - lodoarachidonate - Thyroid - Growth - Autoregulation - FRTL-5
