title: Nervous tissue thiamine metabolism in vivo. I. Transport of thiamine and thiamine monophosphate from plasma to different brain regions of the rat.
abstract: The transport of thiamine (T) and thiamine monophosphate (TMP) across the blood-brain barrier was measured in vivo in the rat. Different doses of [14C]T (15-550 nmol) and [14C]TMP (11-110 nmol) were injected into the femoral vein. The content of T and its phosphoesters in blood and brain tissue (cerebellum, pons, medulla and cerebral cortex) 20 s after the injection was determined radiometrically after electrophoretic separation. Blood flow and blood volume in the same regions of the brain was also determined. Both T and TMP entered rapidly the cerebral tissue, where they were found chemically unmodified. The cerebral tissue extracted less than 7% of plasma T. At physiological plasma T concentrations, the rate of transport ranged from 0.43 to 0.65 nmol X g-1 X h-1 with only minor differences among the various regions. T was transported into the nervous tissue by two separate mechanisms: one saturable, that at physiological plasma T levels accounted for 95% (cerebellum) to 91% (cerebral cortex) of the total T taken up, and one non-saturable, that was most efficient in the cerebral cortex. The Km (half-saturation constant) of the former transport mechanism ranged from 1.95 to 2.75 nmol X ml-1 in the 4 areas investigated. Vmax (maximal transport rate) values ranged from 6 to 9 nmol X g-1 X h-1, the highest value being found in the cerebellum. The overall transport rate of TMP was on average 5-10 times as low as that of T and also showed a saturable and a non-saturable component. Both components were slower than those observed for T.
mesh_terms: D000818:Animals; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D004912:Erythrocytes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051381:Rats; D013831:Thiamine / Q000097:blood / Q000378:metabolism*; D013833:Thiamine Monophosphate / Q000097:blood / Q000378:metabolism
chemical_list: D013833:Thiamine Monophosphate; D013831:Thiamine