Effects of ions and metabolic inhibitors on thyroid-stimulating-hormone stimulation of glucose oxidation in thyroid slices

Abstract

The thyroid-stimulating hormone (TSH) stimulation of glucose oxidation by thyroid slices does not seem to be dependent on the ionic composition of the buffer since the effect was observed in Krebs-Ringer bicarbonate, Krebs-Ringer phosphate, KCl, NaCl, sodium phosphate, potassium phosphate, Tris and glycylglycine buffers. A concentration of ouabain which inhibited I − trapping by thyroid slices had no effect on TSH stimulation of glucose oxidation. The observations suggest that the effect of TSH on glucose oxidation is not dependent upon its stimulation of cell-membrane ATPase (EC 3.6.1.4). Although NaF and p-hydroxymercuribenzoate by themselves increased thyroid-slice glucose oxidation, they inhibited the response to TSH. Dinitrophenol and iodoacetate inhibited both basal and TSH augmented glucose oxidation. Dicumarol had no effect on basal glucose oxidation but also decreased the TSH effect. All of these inhibitors abolished the TSH increase in TPN + levels and most of them were associated with a decrease in TPN + and TPNH. Although explanations for the results with the inhibitors themselves are not apparent, their effect on TSH responsiveness suggests that energy-yielding reactions are necessary.