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

Manuscript received 13 November 1997. Initial reviews completed 26 January 1998. Revision accepted 1 July 1998.

Monica C. Schaeffer^*, , Denise Gretz^*, Dorothy W. Gietzen, and Quinton R. Rogers^**

^* USDA, Western Human Nutrition Research Center, Presidio of San Francisco, CA 94129 and Departments of  Anatomy, Physiology and Cell Biology and ^** Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA 95616

Vitamin B-6 is a cofactor in many reactions of nitrogen metabolism. Deficiency 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 250×) the National Research Council recommended level of pyridoxine HCl (7 mg/kg) for 10 wk and measured serum amino acids, amino acids and neurotransmitters in brain regions and the binding properties of serotonin receptors in the cerebral cortex using a ketanserin binding assay. Rats were decapitated, and unheparinized blood was obtained. In the caudate nucleus, concentrations of glutamate, threonine, taurine, methionine, -amino-butyric acid and the sum of the essential amino acids in groups 10X and 100X were ~130 to 180% of control levels (P < 0.05); groups 1X, 175X and 250X were not different. A similar pattern was seen in the serum for serine, glycine, aspartate and ornithine; the latter two amino acids increased to over 200% of control in group 100X. In the ketanserin binding assay, both the antagonist binding affinity and the maximal number of binding sites were higher for group 100X than for 1X, 175X and 250X, and were higher for 10X than for 1X. Norepinephrine in the raphe nucleus followed a similar biphasic pattern. Excess dietary pyridoxine affected brain and serum concentrations of some amino acids and binding properties of cortical serotonin receptors in a biphasic pattern over the range of concentrations fed in this study.

The Journal of Nutrition Vol. 128 No. 10 October 1998, pp. 1829-1835
Copyright ©1998 by the American Society for Nutritional Sciences