The Effect of Ouabain on Thyrotropin-stimulated Respiration of Thyroid Slices.

Previous studies on isolated thyroid cell membranes (1) revealed the presence of an adenosinr triphosphatase (ATPase) activity in these membranes nhicsh showed features characteristic of Na+ and K+ transport by intact cells, and which was enhanced by thyrotropin (TSH’). This ATPase activity was stimulated by Na+ and K+ and required both ions together, was inhibited by ouabain, was Mg++-requiring, and hydrolyzed adenosine triphosphate in preference to inosinr triphosphate. The hydrolysis of ATP by the cell membranes in the presence of ‘I’SH seemed in all respects to represent an augmentation of this “?;a+-K+ pump,” and it was suggested that the primary effect of TSH may be on Na+ transport in the intact thyroid cell. Wolff and Halmi (2) have likewise demonstrated an Na+-K+-stimulated, ouabain-sensitive ATI’ase in the “nuclear” (cell membranrcontaining) fraction of thyroid homogenates and have shown that it is enhanced by stimulation in viva with TSH. Stimulation in vitro by TSH of the oxygen consumption of thyroid slices has been reported by Paal (3), hndcrson and Alt (4), Canzanelli and Rapport (5), and Freinkcl (6), and the question arises as to whether this stimulatory effect of TSH on respiration is likewise inhibited by ouabain and dependent upon the presence of sodium. In the present investigation those factors found to influence thyroid cell membrane ATPase were studied in relation to their effect on cellular respiration. It was observed that the responses in cellular respiration closely paralleled cahangrs known to occur in ,YTl’asr activity.