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

Pyridoxine, regardless of serotonin levels, increases production of 5-hydroxytryptophan in rat brain

BACKGROUND

The aim of this study was to evaluate effects of pyridoxine and butylated hydroxytoluene (BHT) on lipid peroxidation and on levels of 5-hydroxytryptophan and serotonin.

METHODS

Thirty rats (30 days of age) were used in the survey, measuring levels of lipid peroxidation (TBARS), hemoglobin, 5-hydroxytryptophan (5-HTP), and serotonin (5-HT) after intraperitoneal (i.p.) injections of 4 and 10 mg/kg/day of pyridoxine HCl during 20 days and a single dose of 2 microM/kg (440 microg) of BHT.

RESULTS

Levels of TBARS and 5-HTP increased considerably (p <0.05) in all vitamin- and/or BHT-treated groups, and 5-HT increased partially (p <0.05) only in B(6) with or without BHT-treated groups compared with control group.

CONCLUSIONS

Results suggest that pyridoxine plays a role in tryptophan metabolism, increasing production of 5-HTP.

Dose-dependent effects of glutamate in pyridoxine-induced neuropathy

In order to explore the effects of glutamate in a pyridoxine megadose-induced neuropathy, rats were received glutamate either 0.5 or 1 g/kg/day orally with or without pyridoxine 0.8 g/kg/day intraperitoneally for 14 days. The animal's motor coordination, the muscle power and the thermal threshold were observed daily. The nerve conduction velocity was measured at day 0 and day 15 of the treatment. Glutamate either 0.5 or 1 g/kg/day appeared to have no effect on motor coordination, the nerve conduction velocity and the muscle power score compared with control. However, the thermal response latency was significantly decreased (from day 9) in animals treated with 1 g/kg/day glutamate. In pyridoxine-induced neuropathy rats, glutamate 0.5 g/kg/day significantly decreased the effects of pyridoxine on the sciatic nerve conduction velocity, the muscle power score and the motor coordination. Interestingly, glutamate at a dose of 1 g/kg/day worsened the neurotoxic effects cause by pyridoxine.

Effects of long-term parenteral administration of vitamin B6 on B6 status and some aspects of the glucose and protein metabolism of early-weaned piglets

The present experiment aimed to determine the effect of feeding level and parenteral supplements of vitamin B6 (pyridoxine) on B6 status as well as on glucose, C-peptide, insulin, alpha-amino-N and urea after a gastric bolus of glucose in weaned piglets; the plasma tryptophan, xanthurenic acid and kynurenine responses to a gastric bolus of tryptophan were also measured. Forty-two piglets weaned at 2 weeks of age were distributed in seven blocks of six animals each. Within each block, the animals were assigned to the following factorial treatments: two levels of feeding (28 (F28) and 56 (F56) g/kg(0.75) per d) administered by gastric-tube feeding and three levels of parenteral (intramuscular injections) vitamin B6 (0 (B60), 15 (B615) and 30 (B630) mg/d). In B60 piglets, a decrease of 30 % and 20 % in erythrocyte and plasma pyridoxal-5-phosphate respectively, were observed during the 2 weeks post-weaning. In supplemented piglets, the erythrocyte pyridoxal-5-phosphate was maximised in B615 piglets at a level 3-4 times higher than in B60 piglets (P < 0.003). However, in plasma the maximal pyridoxal-5-phosphate concentration was reached in F28-B630 piglets (P < 0.058). The glucose and insulin responses to a gastric bolus of glucose were lower, and the post-bolus decrease of glucose was slower, in F28 than in F56 piglets (P < 0.0001). The insulin:C-peptide ratio was 25 % greater in B615 piglets (P < 0.082). After the bolus of glucose, the aminoacidaemia decreased differentially according to treatments (P < 0.047), while the uraemia was at least 2-fold higher (P < 0.001) in F28 piglets than in F56 piglets and tended to be maximised in B630 piglets (P < 0.074). The response of plasma tryptophan to the gastric bolus of tryptophan was 11 % lower in B630 piglets (P < 0.057). The plasma concentration of kynurenine increased continuously during the post-bolus period and this response was more marked in F56 (P < 0.002) and in B630 piglets (P < 0.02). Xanthurenic acid was undetectable in any of the treatments. The measurements on pyridoxine status suggest that the present basal dietary level of B6 (7.7 mg/kg) was not sufficient to cover the metabolic needs. For many criteria, an optimal level was reached at 15 mg/d parenteral B6 but the response of urea to glucose bolus suggests that 30 mg/d was detrimental. Further studies are necessary to determine the dietary level of B6 equivalent to the present optimal parenteral supplements and its eventual effects on B6 status and post-weaning growth performance of piglets.