Biochemical Modulation of Blood-Brain Barrier Permeability

Abstract

The permeability of hydrophilic substances in the blood-brain barrier (cerebral capillary endothelium) is small, of the order of 1–10 nm/s (Table 1). Most substrates of brain metabolism are hydrophilic and few lipophilic metabolites exist naturally in plasma. The substrates cross more readily than do the inert non-electrolytes having apparent permeabilities at ordinary plasma concentrations of the order of 100–1000 nm/s. The best example of such a substance is D-glucose, the apparent permeability of which is 350 nm/s at ordinary plasma concentrations, compared to L-glucose which has a permeability of only 2 nm/s (Table 1).