Direct and Synergistic Interactions of 3,5,3′-Triiodothyronine and the Adrenergic System in Stimulating Sugar Transport by Rat Thymocytes

Abstract

A B S T R A C T Isolated rat thymocytes were preincubated with various catecholamines, alone and together with 3,5,3'-triiodothyronine (T3), and the accumulation of the glucose analogues, 2-deoxy-D-glucose (2-DG) and 3-0-methylglucose (3-0-MG), was then measured. Epinephrine induced a time-and dose-dependent increase in the 15-min accumulation of 2-DG; at a concentration of 100 ,uM epinephrine, the effect was evident after a preincubation period of only 5 min. The lowest concentration of epinephrine at which a significant effect was evident was 1 uM. Epinephrine also produced a dose-dependent increase in the accumulation of 3-0-MG, and the lowest concentration at which a significant effect was evident was again 1 uM. Isoproterenol, a f-adrenergic agonist, like epinephrine, increased the accumulation of 2-DG, whereas the aagonist, phenylephrine, had no effect. The response to epinephrine was inhibited by the ,8-antagonist, alprenolol, but the a-antagonist, phentolamine, had no effect. As previously demonstrated, T3 increased 2-DG accumulation, and like epinephrine, its effect was blocked by alprenolol. Neither T3 (0.1 nM) nor epinephrine (0.1 uM) had any effect when acting alone, but when added together at these concentrations, they significantly increased the accumulation of both 2-DG and 3-0-MG. Neither T3 with isoproterenol nor T3 with phenylephrine produced a comparable synergistic effect. But T3 (0.1 nM) acting with isoproterenol (0.1 ,M) and phenylephrine (0.1 ,\M) together, synergistically increased 2-DG accumulation. In addition, the a-antagonist, phentolamine, which alone had no effect, inhibited the synergistic effect induced by T3 and epinephrine. The effects of epinephrine and T3 alone, as well as their combined synergistic effect on 2-DG accumulation, were not blocked by the inhibitor of protein synthesis, puromycin.Received for publication 5 September 1979 and in revised form 5 November 1979. 958 From these results we conclude the following: (a) the stimulatory effect of the catecholamines on the accumulation of 2-DG and 3-0-MG reflects an action at the 13-receptor; (b) the synergistic interaction between T3 and epinephrine requires the participation of both 18-and a-adrenergic components; (c) T3 and epinephrine act on 2-DG and 3-0-MG accumulation through a common mechanism or inter-related mechanisms, probably mediated at the 3-adrenergic site; and (d) these effects of T3 and epinephrine, alone and together, are independent of new protein synthesis. These results suggest that, with respect to the response we are describing, T3 and epinephrine do not act on nuclear mechanisms;, but may act instead at the level of the plasma membrane.

Studies of the mechanism by which 3,5,3'- triiodothyronine stimulates 2-deoxyglucose uptake in rat thymocytes in vitro. Role of calcium and adenosine 3':5'-monophosphate.

“…DISCUSSION We have previously suggested that the T3-induced increase in the uptake of 2-DG and 3-0-MG by rat thymocytes in vitro reflects a primary action of thyroid hormone at the level of the plasma membrane that enhances the inward transport of sugar (1,2). The present studies, we believe, provide strong evidence for this view and shed light on the antecedent events that seem to be part of the mechanism of the T3 effect.…”

“…In previous experiments, we have shown that T3 and epinephrine independently stimulate 2-DG uptake in rat thymocytes, and interact synergistically in this respect (1,2). Therefore, experiments were performed to compare the properties of the stimulatory response of the 2-DG uptake to epinephrine with those of the response to T3.…”

“…This effect is prompt and independent of new protein synthesis. T3 and epinephrine act synergistically to increase sugar uptake into the cell (2), and, in the presence ofboth epinephrine and insulin, 2-DG uptake is enhanced by a physiological (5 pM) concentration of T3 (3).…”

In vivo stimulation of sugar uptake in rat thymocytes. An extranuclear action of 3,5,3'-triiodothyronine.

“…We have previously demonstrated that 3,5,3'-triiodothyronine (T3)' increases the uptake ofthe glucose analogue 2-deoxyglucose (2-DG) in isolated rat thymocytes in vitro (1)(2)(3)(4)(5). This effect of T3 is evident within 20 min after the addition of the hormones; it is independent of new protein synthesis, is calcium-dependent, and is mediated by an increase in cellular cyclic AMP (cAMP) concentration secondary to an increase in adenylate cyclase activity.…”

Specific Binding Sites for Triiodothyronine in the Plasma Membrane of Rat Thymocytes

“…Thus, the effect is rapid, is independent of new protein synthesis, and is mediated via an increase in cellular cyclic (c)AMP concentration, as a consequence of an increase in the activity of adenylate cyclase (2)(3)(4), an enzyme that resides within the plasma membrane. Furthermore, epinephrine, which is known to initiate its action upon binding to its plasma membrane receptors and thence activating adenylate cyclase, produces with T3 a synergistic increase in the 2-DG uptake (5 At the end of the incubation period, triplicate 250-Ml aliquots of reaction mixture were quickly removed and applied onto 0.3-um Millipore filters (Millipore Corp., Bedford, MA) under vacuum. The membranes were then quickly washed three times with 2.5 ml of ice-cold buffer.…”