Peroxide formation and glucose oxidation in calf thyroid slices: regulation by protein kinase-C and cytosolic free calcium

Abstract

We have determined the effects of tetradecanoyl phorbol acetate (TPA) and of the calcium ionophore A23187 on two thyroid responses to TSH previously reported to be cAMP-independent. We observed that TPA and A23187, at doses of 1.0 microM, stimulated both hydrogen peroxide generation and glucose oxidation in calf thyroid slices. A subthreshold dose of A23187 (0.1 microM) added to a submaximal dose of TPA (0.5 microM) acted synergistically, stimulating H2O2 production to the same degree as a maximally effective dose of TSH (50 mU/ml). Forskolin (25 microM), a direct stimulator of adenylate cyclase, actually inhibited both glucose oxidation and hydrogen peroxide generation. Lithium chloride (25 mM) had no effect on either response, either in the basal state or with TSH stimulation. The calcium channel antagonist verapamil (50 microM) decreased the basal activity of glucose oxidation and peroxide generation but did not substantially inhibit the effect of TSH on H2O2 generation under the conditions studied. These data support the concept that TSH induces changes in the thyroid phosphatidylinositol metabolism which activates protein kinase-C (c-kinase) and raises cytosolic free calcium. These events appear to act in concert to mediate certain metabolic responses in differentiated thyroid tissue.