Fig 2. Biliary biopterin excretion after loading rats with 6RBH₄ with and without prior administration of probenecid.

Samples were collected from the same rats as those in Fig 1. The bile was collected from the bile duct, and BP levels and BH₄ fractions (BH₄%) were determined following experimental procedure (A) of Materials and Methods. (a) Biliary BP concentration (lower panel) and the BH₄% (upper panel). One group of rats received “BH₄ alone” (open triangles), and the other, “BH₄ + Pbc” (closed triangles). (b) Exponential least-square fitting of biliary BP outflow: “BH₄ alone”; BP(t) = 47.2 • e^−0.007t, correlation coefficient |R| = 0.99. “BH₄ + Pbc”; BP(t) = 37.2 • e^−0.007t, |R| = 0.99. (c) Cumulative BP excretion in the bile. Data in (a) are means ±S.E. of n = 4–6 for “BH₄ alone” and n = 5–7 for “BH₄ + Pbc”. Some error bars are hidden behind symbols. Data in (b) are mean values in (a). Paired t-test, ^††P<0.01; Student’s t-test, **P<0.01.