In vitro effects of arachidonic acid and of inhibitors of its metabolism on the dog thyroid gland.

Incubation of dog thyroid tissue with arachidonic acid (10 to 200 microM) led to the following events: --low conversion to prostaglandins E2 and F2 alpha: 0.07% and 0.02% per hour and 100 mg tissue, respectively --inhibition of the stimulatory effect of low concentrations of TSH on thyroid secretion: the secretory effect of supra-maximal concentrations of TSH and of dB-cAMP was unaffected --inhibition of the cyclic AMP accumulation induced by TSH: this effect was inhibited neither by indomethacin nor by ETYA; cyclic AMP accumulation in response to cholera toxin or PGE1 was unaffected --no effect on cyclic GMP level --stimulation of thyroid proteins iodination. ETYA, but not indomethacin, depressed the iodination of thyroid proteins in resting and stimulated tissue. These data show that arachidonic acid-or a metabolite-can modulate thyroid responsiveness to TSH and suggest that lipoxygenase-products of arachidonic acid metabolism could be involved in thyroid proteins iodination.