Excess L-tryptophan (L-Trp) in the diet decreases fetal body weight. However, the relationship between L-Trp concentration and its effects on maternal, placental, and fetal growth are not well-understood. We investigated the effects of excess L-Trp intake on maternal, placental, and fetal growth. Female mice were fed a 20% casein diet (control diet) or control diet plus 2% or 5% L-Trp during gestation. Pup weights did not differ between the control (L-Trp intake: 0.04 g/kg body weight (BW)/day) and 2% L-Trp groups (L-Trp intake: 3.3 g/kg BW/day), but were significantly lower in the 5% L-Trp group (L-Trp intake: 7.0 g/kg BW/day) than in the control and 2% L-Trp groups. These results show that less than 3.3 g/kg BW/day L-Trp intake in pregnant mice during gestation does not affect fetal growth or L-Trp homeostasis in the placenta or fetus.
Calorie restriction leads to a change in the metabolism of nutrients. Nicotinamide is biosynthesized from l-tryptophan. We attempted to determine the effects of food restriction on the biosynthesis of nicotinamide from l-tryptophan. Weaning male rats were fed a conventional chemically defined diet without preformed niacin for 63 d. However, the food intake was restricted to 80 and 65% of the intake of the ad libitum-fed control group of rats. The 24-h urine samples were periodically collected, and the urinary excretion of nicotinamide and its catabolites was measured. The conversion percentages were lower in both restricted groups than in the ad libitum-fed control group during the experimental period (control group, 1.37 ± 0.24%; 80%-restricted group, 0.20 ± 0.04%; 65%-restricted group, 0.15 ± 0.02%; control vs. restricted groups, p < 0.01). Food restriction, even at mild level, suppressed the conversion of l-tryptophan to nicotinamide when compared to the ad libitum-fed control group.
B-group vitamins are involved in the catabolism of 2-oxo acids. To identify the functional biomarkers of B-group vitamins, we developed a high-performance liquid chromatographic method for profiling 2-oxo acids in urine and applied this method to urine samples from rats deficient in vitamins B1 and B6 and pantothenic acid. 2-Oxo acids were reacted with 1,2-diamino-4,5-methylenebenzene to produce fluorescent derivatives, which were then separated using a TSKgel ODS-80Ts column with 30 mmol/L of KH2PO4 (pH 3.0):acetonitrile (7:3) at a flow rate of 1.0 mL/min. Vitamin B1 deficiency increased urinary levels of all 2-oxo acids, while vitamin B6 deficiency only increased levels of sum of 2-oxaloacetic acid and pyruvic acid, and pantothenic acid deficiency only increased levels of 2-oxoisovaleric acid. Profiles of 2-oxo acids in urine samples might be a non-invasive way of clarifying the functional biomarker of B-group vitamins.
Summary Nicotinamide and serotonin are synthesized from l-tryptophan in mammals. It is important to know the nutritional factors affecting the synthesis of nicotinamide and serotonin. We investigated the effects of amino acid composition. Young adult rats were fed ad libitum for 21 d a low-protein (9% casein) diet([1] control), or one of the low protein diets supplemented with following amino acids: [2] glycine, l-threonine, and l-cystine, [3] l-threonine and l-cystine, [4] glycine and l-cystine, and [5] glycine and l-threonine. The amounts of glycine, l-threonine and l-cystine supplementations were 2%, 0.078%, and 0.2%, respectively, and the amino acid contents of all diet were adjusted with supplementation of l-glutamic acid. The body weight gain, food efficiency ratio, and the amino acid nutrition biomarker, which is the urinary excretion ratio of (N
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