THE UPTAKE OF DL-LYSINE-H3 INTO THE NERVOUS SYSTEM AS COMPARED WITH OTHER TISSUES IN EUTHYROID AND DYSTHYROIDAL MALE RATS

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Abstract
In 2 separate experiments it was shown that DL-Lysine-H3 uptake is lower in hyperthyroid rats and higher in hypothyroid animals than normal. This is believed to be largely due to metabolic considerations which effect the turnover rate of amino acids in brain and tissue proteins rather than being related to an increase or decrease in the synthesis of the total amount of protein. It was observed that the brain reacted to variations in thyroid state of the animal in a manner comparable to other tissues. A method is described whereby one can study the uptake of lysine and presumably other amino acids into nerve cells. With lysine, enough labeled amino acid entered the cells to permit chromatographic identification of the injected material as well as quantitative counting by liquid scintillation procedures. Uptake of lysine into the ventral horn motor neurons of the spinal cord was 25-30 times higher than was observed in the ventral horn tissue as a whole. Thus, the total uptake in a region of mixed nerve cells, supporting tissues and nerve fibers reflects only the uptake in a heterogenous tissue where a relatively high concentration of amino acid uptake by nerve cells is camouflaged by the relatively low uptake in vascular and glial tissue.