Abstract
Fate of methionine in the blood of mice were studied by a complex radiotracer technique. Absorption results of 3 radioactive methionines indicated that the uptake of methionine was very fast and about 92.8% of the dose was taken up from the blood stream into organs and tissues within 5 min. after bolus intravenous injection.
Since 5 min, after the injection, decrease of the radioactive concentration in the blood continued for 30 min., but it was slower compared to decrease within the first 5 min.. A major absorption of blood methionine into organs and tissues has been found to occur within a few minutes after i.v. injection of a tracer of radioactive methionines. Results of continuous counting and recording of 14CO expiratory rate indicated that there was the most intensive metabolic period occured 5 min.-20 min. after i.v. injection of 2 14C-methionines. Therefore, a good time-dependent sequence between the absorption and consumption of blood methionine was found, though it was a little difficult by regular sampling techniques to find such a fine correlation. Both radiorespirometric plateau height and 14CO2 expiratory rate (% of dose) of [1-14C] Met was 3 times higher than these of [methyl-14C] Met.
Excretion of a radioactive moiety of labeled methionines ito feces was miner and those of a radioactive moiety of labeled methionines into urine were attibuted by the specifically labeled position or radioactive atom, 35S or 14C. The distribution of radioactivity in organs and tissues was estimated by a liquid scintillation counting. Also it was determined by a freeze-dried microautoradiography for diffusible components. Both results indicated that a majority of the administered methionine was utilyzed in muscle and skin, and about 50 % of dose were disposed at 8 hr. after the injection. Such an organ as pancreas was actively produced and excreted zymogen granules from the pancreas gland cells. It was suggested that a gentle reascending curve of the blood concentration during 30-90 min. after i.v. injection was attrjbuted to supply of serum proteins which were synthesized from radioactive methionines in the liver.
