Effects of ions on TSH stimulation of P-32 incorporation into thyroid slice phospholipid

Abstract

Effects of cations and ouabain on thyroid-stimulating hormone (TSH) stimulation of P32 incorporation into dog thyroid slice phospholipid were studied. Omission of Na+ from the buffer markedly decreased base-line incorporation and abolished the TSH stimulation. Addition of 12 m[image] Na+ restored TSH action without increasing base-line incorporation. Ca++ and Mg++were not essential for TSH stimulation of P32 incorporation. Ouabain inhibited TSH stimulation of P32 incorporation into phospholipid during both a 45- and 180-min. incubation without modifying the effect of TSH on glucose oxidation. These findings indicate that the TSH stimulation of P32 incorporation into phospholipids has an absolute dependence on Na+ and is further influenced by the ionic composition of the medium. This dependence on Na+ is further supported by the observation that ouabain inhibited TSH action. Since the TSH effect on glucose oxidation is not dependent on the ionic composition of the medium or abolished by ouabain, it is apparent that it is not secondary to the TSH stimulation of P32 incorporation into phospholipid.