Plasma L-Methionine Levels Following Intravenous Administration in Humanss

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Abstract
Methionine detns. were made by a microbiologic method using plasma from heparinized blood. Eleven normal human cf & were used as controls. After a 12-hr, fast, blood was drawn for detn. of the level of plasma methionine. Fifty ml. of 3% dl-methionine was then inj. intraven., blood samples being drawn 15, 30, 60, 120, and 180 mins. after the injn. Methionine detns. in urine excreted during the test period and during 12 hrs. preceding the test were also made. There was a sharp rise in plasma concn. immediately following injn. which decreased rapidly in the first 30 mins. and then much more slowly. In a 3-hr, of observation, the plasma level did not return to the fasting value. Considerable variation in the absolute values for the various points on the curve were observed. The excretion of methionine was most rapid in the first 15-30 mins., when blood levels were highest, but the amt. excreted at any time was low when compared with the original amts. given. It was apparent that excretion explained the disappearance from the plasma of only a negligible portion of the 750 mg. of the L isomer given, and that at these plasma levels no evidence of a limiting rate of renal tubular reabsorption for methionine was seen.