INCREASED BLOOD-BRAIN-BARRIER PERMEABILITY OF AMINO-ACIDS IN CHRONIC HYPERTENSION

A previous communication from this laboratory reported that brain upta ke of libenzapril, a small polar molecule, was enhanced in chronic hyp ertension (1). The objective of this investigation was to determine if this was a more generalized phenomenon. Therefore, experiments were u ndertaken to examine the effect of chronic hypertension on the brain u ptake of tryptophan (an amino acid with high brain permeability) and g lutamic acid (one with low permeability). Brain concentrations of thes e two amino acids were 5- to 12-fold greater in chronic hypertensive r ats, as compared to normotensive rats; the corresponding brain uptake index (BUI) values were 2- to 5-fold higher in the former group. Since blood-brain barrier transport of amino acids involve both saturable ( carrier) and non-saturable (most likely, diffusion via pores) mechanis ms, data from this study show that hypertension can enhance BBB transp ort of amino acids by affecting one or both of these pathways.