Effects of thyrotropin on thyroidal phospholipid and adenosine 5'-triphosphate metabolism.

Thyrotropin stimulates the incorporation of 32P into phospholipids of thyroid slices incubated with 32P04. To determine whether this effect could be secondary merely to an increase in the specific activity of the terminal (y) P of ATP, a precursor of phospholipid P, the effect of thyrotropin on calf thyroid slice ATP was measured with an assay which is selective for ATP-T-~~P specific activity. Thyrotropin increases the specific activity of lipid 32P uniformly without altering that of ATP-T-~~P, indicating that it exerts its effect at a step beyond ATP in the sequence of phospholipid biosynthesis. There was no significant effect of thyrotropin on the ATP content of thyroid slices.