Stimulation of arachidonic acid release from thyroid phospholipids.

The present study demonstrates that exposure of pig thyroid slices to thyrotropin stimulates the arachidonate release from endogenous phospholipids. The experiments with 14C-arachidonic acid show that the release of arachidonic acid is mostly from phosphatidylcholine, phosphatidylinositol and neutral lipids. The liberation of arachidonate from thyroid phospholipids is Ca2+ dependent. The addition of calcium ionophore A23187 to medium augments the release of arachidonate. Addition of ionophore and egzogenous Ca2+ markedly stimulates the arachidonate release, what suggests that thyroid phospholipase A2 can be regulated by the extend of saturation of the enzyme with Ca2+. The arachidonate release from phospholipids caused by thyrotropin is potentiated by adenosine. This effect shows that adenosine modulates TSH action and supports the idea that adenosine takes part in the physiological regulation of thyroid cells.