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NIACIN AND NIACINAMIDE ACCUMULATION BY RABBIT BRAIN SLICES AND CHOROID PLEXUS IN VITRO
Authors:REYNOLD SPECTQR  PAUL KELLEY
Institution:Division of Clinical Pharmacology, Departments of Medicine and Pharmacology, University of Iowa College of Medicine, Iowa City, IA 52242, U.S.A.
Abstract:The transport into and release of14C-labeled niacin and niacinamide from rabbit brain slices and isolated choroid plexuses were studied. In vitro, both brain slices and choroid plexus concentrated 14C by specific, energy-dependent mechanisms when 14C]niacinamide was added to the incubation medium. The saturable accumulation velocities, which were linear for 30 min, depended, in part, on incorporation of the 14C]niacinamide into NAD. The XT and Ymax for 14C accumulation with 14C]niacinamide in the medium by brain slices and choroid plexus were 0.80 μM and 1.45 μmolkg?1 (30 min)?1, and 0.23 μM and 18.6 μmol kg?1 (30 min)?1 respectively. In vitro, the choroid plexus, unlike brain slices, vigorously concentrated 14C by a separate, specific energy-dependent process when 14C niacin was added to the incubation medium. The saturable accumulation velocity, which was linear for 30 min, depended completely on the metabolism of 14C]niacin. The KT and Ymax for14C accumulation by choroid plexus with 14C]niacin in the medium were 18.1 μM and 439 μmol kg?1 (30 min)?1 respectively. Whether preincubated in 14C]niacin or 14C]niacinamide, choroid plexus released predominantly 14C]niacinamide.
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