The influx of ascorbic acid into the rat's brain.

The influx of [14C]ascorbic acid into the rat's brain through the cerebral capillaries was measured by the steady-state initial-rate technique. Ascorbic acid was found to pass through the capillaries by a carrier-mediated process and by simple diffusion. The carrier system was found to have an apparent Vmax of 1.2 nmol . min-1 . g-1 of cerebral tissue and a Kt of 125 microM. The apparent constant of transfer, Kd, of the diffusional component was 0.98 microliter. min-1 . g-1. The contribution of the cerebral capillaries to the movement of ascorbic acid into the brain is discussed and was found to be the major route of entry into the brain for this vitamin.