[131I]Triiodothyronine transport into rat cerebral cortex slices☆

Abstract As a result of a previous investigation where X-irradiation depressed T 3 accumulation into the rat CNS in a manner which suggested an effect on an enzyme transport system for the hormone, this series of experiments was initiated to determine if there might be any specific evidence for active transport of the hormone into tissue. All the results obtained on increased T 3 accumulation into cortex slices with increasing periods of incubation, the effects of altering substrate concentration or of changing pH could as well be said to relate to active as to the commonly accepted passive mode of transport. However, the inhibition of hormone uptake in the presence of CN − , ouabain and 2,4-DNP suggested an energy-dependent system in which ATP and cytochrome oxidase are involved. Further, the dependence of hormone accumulation in brain slices on Na + is comparable to that observed for amino-acids, which are known to be actively transported. Finally, the slight inhibition of T 3 accumulation in the presence of tyrosine or when slices were incubated in an unoxygenated media or at 0°C strongly suggest that at least a part of the accumulation of [ 131 ]T 3 into rat cerebral cortex slices in vitro is activity mediated. Anatomical studies on incubated rat cerebral cortex slices indicate that marked structural changes in neurons occur very quickly with disruption of membranes occurring after 60 min incubation. Thus, if transport mechanisms are to be studied by such in vitro procedures, they should be limited to the shorter periods (30 min) wherein the neuronal cell membranes remain intact.