Blood–Brain Transport of Thiamine Monophosphate in the Rat: A Kinetic Study In Vivo

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Abstract
To calculate the kinetic parameters of thiamine monophosphate transport across the rat blood-brain barrier in vivo, different doses of a [35S]thiamine monophosphate preparation with a specific activity of 14.8 mCi .cntdot. mmol-1 were injected in the femoral vein and the radioactivity was measured in arterial femoral blood and in the cerebellum, cerebral cortex, pons, and medulla 20 s after the injection. This short experimental time was used to prevent thiamine monophosphate hydrolysis. Thiamine monophosphate was transported into the nervous tissue by a saturable mechanism. The maximal transport rate (Jmax) and the half-saturation concentration (Km) equaled 27-39 pmol .cntdot. g-1 .cntdot. min-1 and 2.6-4.8 .mu.M, respectively. When compared with that of thiamine, thiamine monophosphate transport seemed to be characterized by a lower affinity and a lower maximal influx rate. At physiological plasma concentrations, thiamine monophosphate transport rate ranged from 2.06 to 4.90 pmol .cntdot. g-1 .cntdot. min-1, thus representing a significant component of thiamine supply to nervous tissue.