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. 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 250x) 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, gamma-amino-butyric acid and the sum of the essential amino acids in groups 10X and 100X were approximately 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.

Tissue B-6 vitamer concentrations in rats fed excess vitamin B-6.

Diets containing 1, 10, 100, 175 or 250 times the NRC recommended level of pyridoxine HCl (7 mg/kg) were fed to rats (218 g, 12 per group) to evaluate the effects on tissue B-6 vitamer concentrations. After 10 wk, food intake and body weights did not differ among groups. Overt toxicity was not observed. Tissues were taken from five rats of each group after overnight food deprivation (unfed rats); the remaining seven rats in each group were allowed access to food (fed rats). In plasma of unfed rats, 4-pyridoxic acid and pyridoxal concentrations increased significantly (P < 0.05) with increasing dietary pyridoxine; pyridoxal phosphate was not affected by dietary pyridoxine. Concentrations of pyridoxal phosphate and pyridoxal increased significantly with increasing dietary pyridoxine in erythrocytes of unfed rats. Excretion of urinary B-6 vitamers and 4-pyridoxic acid in a 24-h period increased with dietary pyridoxine in fed rats. As dietary pyridoxine was increased, kidney pyridoxal concentrations increased significantly in fed rats only. Dietary pyridoxine did not affect vitamer concentration in muscle and liver of either unfed or fed rats, or in brain of unfed rats. Muscle glycogen phosphorylase, which contains pyridoxal phosphate, was not affected by dietary pyridoxine. There was a marginally significant (P = 0.058) increase in erythrocyte alanine, but not in aspartate, aminotransferase activity with increasing dietary pyridoxine. Plasma concentration of pyridoxal phosphate, which is used as a measure of vitamin B-6 status, did not reflect intake of pyridoxine in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Excess dietary vitamin B-6 alters startle behavior of rats.

Excessive intakes of vitamin B-6 can produce peripheral nervous system abnormalities, but few reports of central nervous system effects exist. We measured startle response, a central nervous system reflex, in rats fed excess pyridoxine to determine if subtle effects on central nervous system function could be detected. Female Long-Evans rats (218 g; n = 12) were fed either 1, 10, 100, 200 or 300 times the requirement of pyridoxine HCl (7 mg/kg) for 7 wk. Startle behavior was assessed weekly in chambers that allowed quantification of movement in response to stimuli. Food intake and body weights did not differ among groups (P > 0.1), and urinary vitamin B-6 excretion reflected intake (P < 0.001). Overt toxicity was not observed. There was a marginally significant effect of pyridoxine intake over time (P = 0.053) on the amplitude of response to a startling acoustic stimulus (117 dB, 40 ms) administered alone; the response appeared attenuated at the three highest pyridoxine concentrations. When the same stimulus was preceded by either a 70- or 75-dB prepulse (40 ms), responses of groups fed the two highest pyridoxine concentrations were significantly reduced relative to those fed the two lowest concentrations (P < 0.05). No effect of diet was seen with a startling tactile stimulus. Changes in central nervous system function were detected in rats fed excess vitamin B-6 using techniques of startle behavior measurement.

Insensitivity of the tryptophan-load test to marginal vitamin B-6 intake in rats.

The tryptophan-load test for vitamin B-6 nutritional status was administered to adult female Long-Evans rats fed graded levels of pyridoxine hydrochloride (PN.HCl) in two experiments, and its sensitivity to marginal vitamin B-6 intake was evaluated. In Experiment 1, rats were 4-h meal-fed an AIN-76A (20% casein) diet devoid of PN.HCl for 3 wk, then repleted (n = 12) for 6 wk with 4-h pair-fed meals of either 0.25, 0.5, 1.0 or 7.0 (control) mg PN.HCl/kg diet. In Experiment 2, rats (n = 16) were pair-fed for 10 wk either 0.0, 0.5, 1.0 or 7.0 (control) mg PN.HCl/kg diet, with 24-h access to food. Vitamin B-6 nutritional status was assessed at the end of each experiment. Except in rats fed 0 mg PN.HCl/kg diet, mean body weights were not significantly different among diet groups of either experiment. Plasma pyridoxal phosphate (PLP), pyridoxal and total vitamin B-6 concentrations, determined by HPLC, were very sensitive to gradations in dietary PN.HCl concentrations (P less than 0.05). Red blood cell endogenous and PLP-stimulated alanine and aspartate aminotransferase activity did not statistically differentiate all levels of dietary vitamin B-6, although the calculated activity coefficient for each enzyme (stimulated/endogenous activity) did. Urinary xanthurenic acid excretion following a tryptophan load [24.5 mumol (5 mg) L-tryptophan/100 g body weight, injected intraperitoneally] was significantly (P less than 0.05) elevated compared with controls only in the group fed 0 mg PN/HCl/kg diet. At the tryptophan dose used here, the tryptophan-load test was not useful in detecting marginal vitamin B-6 intake in rats.

Changes in cerebrospinal fluid and plasma amino acid concentrations with elevated dietary protein concentration in dogs with portacaval shunts.

Effects of dietary protein concentration on plasma and cerebrospinal fluid (CSF) amino acids (AA) in dogs with portacaval shunts (PCS) were examined. An 18% protein purified diet (18P) was fed to 4 PCS dogs and 2 controls; at week 10, 2 of the PCS dogs were switched to 36% protein (36P) until week 28. Effects of the diet switch on plasma and CSF AA in 8 normal dogs were determined in another experiment. Neither surgery nor protein level significantly affected average food intake (weeks 10-28). Plasma amino acid patterns typical of PCS animals were observed: phenylalanine and tyrosine increased and branched chain AA decreased with shunting (p less than 0.05). Plasma phenylalanine increased further with 36P in PCS dogs (p less than 0.05), but was not affected by dietary protein concentration in controls. With 36P: CSF arginine, serine, histidine, tryptophan, phenylalanine, glutamate and glutamine increased in PCS dogs; but only arginine decreased in CSF of controls (p less than 0.05). In PCS dogs, significant CSF AA changes with elevated dietary protein were unrelated to plasma AA changes.

Subtle abnormalities of gait detected early in vitamin B6 deficiency in aged and weanling rats with hind leg gait analysis.

Motor abnormalities have been observed in every species made vitamin B6 deficient, and have been detected and quantified early in vitamin B6 deficiency in young adult female Long-Evans rats with hind leg gait analysis. Our objective was to determine if hind leg gait analysis could be used to detect vitamin B6 deficiency in weanling (3 weeks) and aged (23 months) Fischer 344 male rats. Rats (n = 10 per group) were fed: the control diet ad libitum (AL-CON); the control diet devoid of added pyridoxine hydrochloride (DEF); or the control diet pair-fed to DEF (PF-CON). At 10 weeks, plasma pyridoxal phosphate concentration confirmed deficiency in both age groups. Gait abnormalities were detected in the absence of gross motor disturbances in both aged and weanling DEF rats at 2-3 weeks. Width of step was significantly reduced (16%, p less than 0.003) in DEF aged rats compared to AL- and PF-CON. This pattern of response was similar to that reported previously in young adult rats. In weanling rats, pair feeding alone reduced mean width of step (+/- SEM) by 25% compared to ad libitum feeding (2.7 +/- 0.1 vs 3.6 +/- 0.1 cm for PF- vs AL-CON, respectively, p less than 0.05). In DEF weanling rats, width (3.0 +/- 0.1 cm) was increased compared to PF-CON (11%, p less than 0.05) but decreased compared to AL-CON (16%, p less than 0.05). Width of step was significantly altered early in B6 deficiency in rats of different ages and strains and in both sexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of vitamin B-6 status and function of rats fed excess pyridoxine.

We compared the vitamin B-6 status of 12-wk-old rats (n = 12) fed excess (1400 mg/kg diet) or the recommended level (7 mg/kg diet, control) of pyridoxine (PN) hydrochloride to test if excess vitamin B-6 would cause tissue depletion of pyridoxal phosphate (PLP), the active coenzyme form of vitamin B-6. Plasma PLP, tryptophan-load test results, food intake, and tissue and body weights were not different at wk 6. Red blood cell endogenous alanine aminotransferase activity and PLP concentration were elevated (P less than 0.01) in rats fed 1400 mg PN.HCl/kg diet. In contrast, PLP concentration in muscle was significantly lower (P = 0.01) in rats fed excess vitamin B-6 (9.7 +/- 0.8 nmol/g, mean +/- SEM) than in controls (14.9 +/- 1.4). PLP concentration in other tissues, including plasma, was not affected. In rats fed excess vitamin B-6, pyridoxal was increased in all tissues examined (P less than 0.05), and total vitamin B-6 was increased in plasma, red blood cells and kidneys (P less than 0.05). Total glycogen phosphorylase (a + b) activity in the gastrocnemius was not affected, but phosphorylase a activity was increased in rats fed excess vitamin B-6 (P = 0.025). Concentrations of dopamine and metabolites in the caudate nucleus of the basal ganglia were not affected. A transient, but significant, elevation in acoustic startle response, a central nervous system reflex, was observed in rats fed excess vitamin B-6. The depletion in muscle PLP could not hae been predicted by either plasma or red blood cell PLP concentration, although the latter did reflect vitamin B-6 intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of acoustic and tactile startle responses of vitamin B-6 deficient rats.

Vitamin B-6 deficient rats exhibit changes in behavior, sensory function, and other nervous system abnormalities such as convulsive seizures and motor disturbances. Sensorimotor reactivity was evaluated quantitatively by measuring auditory and tactile startle responses in 12 week old female Long-Evans rats fed a diet devoid of added vitamin B-6 (DEF) or a control diet, either ad lib (AL-CON) or pair-fed to deficient rats (PF-CON). Deficiency was confirmed with a tryptophan-load test administered to a separate group of rats fed simultaneously according to the same protocol. At week 18, body weight and feed efficiency were different among groups (p less than 0.001), and were lowest in DEF. Amplitude of response to both acoustic and tactile stimuli was depressed in DEF compared to both control groups, which generally did not differ in response. This effect was seen most dramatically in responses to the acoustic stimulus (p = 0.034), and especially to the first presentation (p = 0.017). Latency to maximum response was not affected by diet. Possible mechanisms for this nervous system abnormality, not previously reported in vitamin B-6 deficiency, are discussed.

Long-term biochemical and physiologic effects of surgically placed portacaval shunts in dogs.

After surgical placement of end-to-side portacaval shunts (PCS), 4 adult mongrel dogs (11.8 to 18.2 kg) were fed purified diets and monitored for approximately 50 weeks for changes in body weight, neurologic status, and an array of clinically important biochemical variables. Two healthy dogs, fed the same diets and maintained in the same environment, were also observed (controls). Body weights were relatively stable over the period of observation. The branched-chain ratio ([valine] + [leucine] + [isoleucine]/[phenylalanine] + [tyrosine]), an index of the degree of change in plasma amino acid concentrations, was significantly lower in dogs with PCS than in controls. Despite this depression in branched-chain ratio, the principals (dogs with PCS) were essentially free of neurologic symptoms. Statistically significant decreases due to portacaval shunting were seen in the serum concentrations of glucose, calcium, urea nitrogen, creatinine, cholesterol, and albumin. Total protein, globulin, and triglyceride concentrations tended to be lower in the serum of principals than in serum of controls, but the differences were not statistically significant. Statistically significant increases due to portacaval shunting were seen in plasma concentrations of total conjugated bile acids and sulfobromophthalein retention. Concentrations of the following compounds tended to be higher in serum of principals than in serum of controls: phosphorus, chloride, uric acid, total bilirubin, lactate dehydrogenase, aspartate transaminase, alanine transaminase, and alkaline phosphatase. Liver biopsy at 7 months after operation showed mild-to-extensive atrophy of hepatocytes, mild-to-extensive fibrosis, and collapsed portal veins in all principals examined.

Methionine requirement of the growing kitten, in the absence of dietary cystine.

This study was conducted to determine the methionine requirement for maximal weight gain and nitrogen retention in growing kittens fed a 24% crystalline amino acid diet containing no cystine. Six male and six female kittens wee fed each of six levels of methionine, 0.45, 0.7, 0.8, 0.9, 1.0 and 1.5% of the diet, for 10 days in a 6 x 6 Latin square design. Diets were made isonitrogenous with alanine and were isocaloric with a calculated metabolizable energy of approximately 5.0 kcal/g. Food intake and body weights were recorded daily, and nitrogen balance for each cat in each 10-day period was determined. On the 7th day of each period, blood was drawn for subsequent analysis of plasma methionine concentrations. From growth response results, the methionine requirement in the absence of dietary cystine was estimated to be 0.07% of the diet for male and female kittens. On the basis of nitrogen balance results, the methionine requirement appeared to be slightly higher, at 0.75% of the diet for both sexes. Plasma methionine concentrations appear to increase exponentially with dietary methionine concentrations, and wee of limited usefulness in estimating the methionine requirement of the kitten in the context of the experimental protocol used here.