L-histidine: effects on sensitivity of cat spinal neurones to amino acids.

L-Histidine enhanced the inhibitory actions of GABA, muscimol and beta-alanine rather than that of glycine on spinal neurones in pentobarbitone-anaesthetised cats. L-Histidine also enhanced the excitatory action of L-glutamate, D- and L-aspartate, L-homocysteate and especially that of quisqualate, whereas the actions of acetylcholine, kainate, N-methyl-D-aspartate and D-homocysteate were more commonly reduced. These actions of L-histidine are best ascribed to an effect on amino acid transport systems, probably of the low affinity type, which therefore appear to be partially responsible for the inactivation of exogenously administered amino acids.