title: Insensitivity of the tryptophan-load test to marginal vitamin B-6 intake in rats.
abstract: 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.
authors.affiliation: U.S. Department of Agriculture, Western Human Nutrition Research Center, San Francisco, CA 94129.
authors.forename: M C
authors.initials: MC
authors.lastname: Schaeffer
authors.forename: D A
authors.initials: DA
authors.lastname: Sampson
authors.forename: J H
authors.initials: JH
authors.lastname: Skala
authors.forename: D K
authors.initials: DK
authors.lastname: O'Connor
authors.forename: D
authors.initials: D
authors.lastname: Gretz
mesh_terms: D000284:Administration, Oral; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D011736:Pyridoxine / Q000008:administration & dosage* / Q000378:metabolism; D051381:Rats; D014364:Tryptophan / Q000378:metabolism / Q000494:pharmacology*; D014977:Xanthurenates / Q000652:urine
chemical_list: D014977:Xanthurenates; C028330:xanthurenic acid; D014364:Tryptophan; D011736:Pyridoxine