Abstract
A method for studying inhibition of dihydrofolate reductase activity in vivo has been described. Mice were given 500 μCi (25 mg) 3H-H 2F/kg intraperitoneally, the tetrahydrofolate (H 4F) formed in liver and gut were separated by DEAE-cellulose column chromatography of tissue homogenates, and the radioactivity in peaks corresponding to H 4F and H 2F was determined. A linear relationship was observed in the inhibition of H 2F-reductase by methotrexate in both liver and intestine when the mice were treated with methotrexate 1 hr before H 2F injection and the tissues were assayed 2 hr later. The recovery of enzyme activity from inhibition by methotrexate in gut and liver was biphasic: a rapid recovery (45% in gut and 72% in liver) within 6 hr was followed by a slower recovery (92% in gut and 98% in liver) in 2 to 3 days. The data presented indicate greater inhibition and slower recovery of H 2F-reductase in intestine than in liver and illustrate the feasibility of assessing H 2F reductase activity in vivo.
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