PATHWAYS OF THYROIDAL PHOSPHORUS METABOLISM: THE EFFECT OF PITUITARY THYROTROPIN UPON THE PHOSPHOLIPIDS OF THE SHEEP THYROID GLAND1, 2

Abstract

Pathways of thyroidal phospholipid metabolism were examined in intact sheep and earlier in vitro findings were confirmed. Acute administration of pituitary thyrotropin (TSH) resulted in increased incorporation of radioactive phosphorus in vivo into all of the phospholipids and water-soluble phospholipid intermediates of sheep thyroid tissue. During incubation of surviving sheep thyroid slices, addition of TSH to the suspending medium effected a prompt increase in the incorporation of radioactive phosphorus into thyroidal phospholipids, and a less pronounced elevation of thyroidal O2 consumption. The actions of TSH could not be duplicated in extrathyroidal tissues nor with other pituitary hormones. Fractionation of lipid extracts disclosed that stimulation of phospholipid metabolism in vitro was not distributed over the entire phospholipid population. Although TSH enhanced the turnover of phosphorus in thyroidal cephalins and phosphoinositide, the major thyroidal phospholipid component, phosphatidylcholine, was minimally affected during 4 hours''incubation. Stimulation by TSH of phospholipid metabolism and the selective effects upon a limited number of thyroidal phosphoglycerides in vitro are discussed with reference to the mechanism of TSH action.