Stimulation in vitro of pathways of glucose oxidation in thyroid by thyroid-stimulating hormone.

Despite many observations on morphologic and biochemical changes in the thyroid after the administration of thyroidstimulating hormone, its exact mechanism of action is still obscure (1, 2). The earliest in vitro effect previously reported was a small increase in oxygen consumption 10 minutes after the addition of TSHl to thyroid slices (3). TSH has also been found to increase phospholipid synthesis and iodide trapping, organification of iodide, and thyroid hormone release, but these effects have been somewhat delayed (4, 5). In a preliminary note we reported evidence for the existence of the hexose monophosphate pathway for glucose metabolism in thyroid slices and the ability of TSH to increase glucose oxidation (6). Stimulation of glucose oxidation was evident 5 minutes after the addition of TSH. Although not as dramatic as its effect on glucose-l-Cl4 oxidation, there was also some increase in glucose-6-C” oxidation to Cl402 when TSH was present. This effect of TSH was not elicited when ACTH, prolactin or growth hormone were tested. The purpose of this communication is to elaborate on this observation as well as to present some information regarding possible mechanism of action.