DIETARY EXCESS OF VITAMIN-B-6 AFFECTS THE CONCENTRATIONS OF AMINO-ACIDS IN THE CAUDATE-NUCLEUS AND SERUM AND THE BINDING-PROPERTIES OF SEROTONIN RECEPTORS IN THE BRAIN CORTEX OF RATS

Vitamin B-6 is a cofactor in many reactions of nitrogen metabolism. De ficiency alters tissue amino acid concentrations but effects of excess vitamin B-6 have not been well described. We fed female rats (218 g, 7 per group) 1 (control), 10, 100, 175 or 250x) the National Research Council recommended level of pyridoxine HCl (7 mg/kg) for 10 wk and me asured serum amino acids, amino acids and neurotransmitters in brain r egions and the binding properties of serotonin receptors in the cerebr al cortex using a ketanserin binding assay. Rats were decapitated, and unheparinized blood was obtained. In the caudate nucleus, concentrati ons of glutamate, threonine, taurine, methionine, gamma-amino-butyric acid and the sum of the essential amino acids in groups 10X and 100X w ere similar to 130 to 180% of control levels (P < 0.05); groups 1X, 17 5X and 250X were not different. A similar pattern was seen in the seru m for serine, glycine, aspartate and ornithine; the tatter two amino a cids increased to over 200% of control in group 100X. In the ketanseri n binding assay, both the antagonist binding affinity and the maximal number of binding sites were higher for group 100X than for 1X, 175X a nd 250X, and were higher for 10X than for 1X, Norepinephrine in the ra phe nucleus followed a similar biphasic pattern. Excess dietary pyrido xine affected brain and serum concentrations of some amino acids and b inding properties of cortical serotonin receptors in a biphasic patter n over the range of concentrations fed in this study.