Abstract
Summary
After a single tracer dose of tritiated pteroylglutamic acid, the uptake, excretion and turnover of radioactivity was measured in the adult rat under steady-state conditions up to 7 weeks after injection. The half-life time of four peaks containing reduced folate pentaglutamates ranged from 3.3 to 4.3 days, indicating a rapid utilization of these liver pools in contrast to the half-life time for plasma radioactivity. The half-life time of the radioactivity excreted in urine is larger than that of liver folates and smaller than that of plasma folates. In view of their rapid turnover and high concentration and variability, it is possible that the pentaglutamate forms in liver serve specific metabolic functions other than simply of a reserve and that folate depletion proceeds at a more rapid rate than previously expected from observations on rates of decrease in plasma folate concentrations.
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