FIGURE 3.

Mean (±SEM) plasma folate content of [¹³C₅]5-formyltetrahydrofolate (circles, M + 5), its metabolite [¹³C₅]5-methyltetrahydrofolate (upward triangles, M + 5), and unlabeled 5-formyltetrahydrofolate (downward triangles, M + 0) after administration of [¹³C₅]5-formyltetrahydrofolate by an enteric-coated caplet (855 nmol; n = 7) (A) and IV injection (214 nmol; n = 9) (B). Note that y axes differ between panels. The change in [¹³C₅]5-formyltetrahydrofolate after IV injection was significant (P < 0.0001) (B). The change in labeled [¹³C₅]5-methyltetrahydrofolate was significant after caplet ingestion (P = 0.0192) (A) and IV injection (P < 0.0001) (B). The change in unlabeled 5-formyltetrahydrofolate was significant after IV injection (P < 0.0001) (B). Repeated-measures ANOVA statistical analyses were used to determine the change in the amount of plasma folate per person after administration of the test dose. IV, intravenous.