In vitro inhibitory effects of an iodinated derivative of arachidonic acid on calf thyroid.

Thyroid glands from different species are capable of iodinating lipids including iodinate derivates of arachidonic acid. The synthesis of an iodoarachidonate derivative (IA) allowed us to explore its possible role in thyroid function; when calf thyroid slices were incubated with IA, an inhibition of 125I uptake (T/M) was observed, with concentrations as low as 10(-8)M. The decrease of the T/M values reached a plateau at 10(-4)M. Arachidonic acid (AA) also decreased 125I uptake. Besides, IA caused a significant inhibition of 125I organification both in thyroid slices and homogenates. AA was without effect on this parameter. The stimulatory effect of TSH on 125I organification was also significantly impaired by IA at 10(-5)M. IA produced a significant decrease in 3H-uridine incorporation into total RNA. This effect is due to a diminution of 3H-uridine uptake as well as to a probable action at a transcriptional step. The addition of MMI did not alter the inhibitory action of IA, and AA was without effect. Therefore we may conclude that IA has an inhibitory action on the thyroid per se at the membrane level and in different subcellular sites. These results suggest a possible role of IA in thyroid autoregulation.