Effects of oestradiol and vitamin B6 on tryptophan metabolism in the rat: implications for the interpretation of the tryptophan load test for vitamin B6 nutritional status

1. The effects of the administration of oestradiol and vitamin B6 on tryptophan metabolism in the rat have been assessed by measurement of the release of 14CO2 from [14C]tryptophan, in vivo, in order to determine whether, and to what extent, the abnormalities of tryptophan metabolism that are associated with oestrogen administration can be attributed to drug-induced vitamin B6 deficiency or depletion. Two positional isomers of [14C]tryptophan have been used; [ring-2-14C]tryptophan as an index of the activity of tryptophan oxygenase (L-tryptophan: oxygen oxidoreductase (decyclizing), EC 1.13.11.11) and [methylene-14C]trytophan as an index of the activity of kynureninase (L-kynurenine hydrolase, EC 3.7.1.3). 2. The administration of 500 μg oestradiol/kg body-weight led to a reduction in the release of 14CO2 from both positional isomers of tryptophan, suggesting that the activities of both tryptophan oxygenase and kynureninase are reduced following oestrogen treatment. The kinetics of the release of 14CO2 from [methylene-14C]tryptophan after the administration of oestradiol were compatible with competitive inhibition of kynureninase by oestradiol or a metabolite. 3. The administration of 10 mg pyridoxine hydrochloride/kg body-weight also reduced the production of 14CO2 from both positional isomers of 14C]tryptophan, suggesting some toxicity of such a high dose of the vitamin. 4. In animals which had received the supplementary dose of vitamin B6, the administration of oestradiol led to further reduction in the production of 14CO2 from [ring-2-14C]tryptophan, suggesting a further reduction in the activity of tryptophan oxygenase, and an increase in the production of 14CO2 from [methylen-14C]tryptophan, but with a delay in the peak of production. 5. These results confirm that there is no induction of tryptophan oxygenase by oestradiol, but rather reduced activity of the enzyme after the administration of a relatively high dose of the hormone. They also confirm that the inhibition of kynureninase by oestrogen metabolites that has been reported previously in partially-purified enzyme preparations also occurs in vivo. 6. It is suggested that the abnormal results of the tryptophan load test that have been reported in women receiving oestrogens, and which have been interpreted as indicating some extent of drug-induced vitamin B6 deficiency, can be accounted for by the inhibition of tryptophan metabolism by oestrogens or their metabolites. Therefore it seems likely that the practice of administering supplements of vitamin B6 to women receiving oestrogens may not be appropriate, and indeed may exacerbate the changes in tryptophan metabolism that result from the administration of oestrogens. The tryptophan load test would appear to be unreliable as an index of vitamin B6 nutritional status in women receiving oestrogens

Non-nutritional uses of vitamin B6

Vitamin B-6 is a water-soluble vitamin, and is readily metabolized and excreted, so it has generally been assumed to have negligible toxicity, although at very high levels of intake it can cause peripheral nerve damage. Nutritional deficiency disease is extremely rare, although a significant proportion of the population shows biochemical evidence of inadequate status, despite apparently adequate levels of intake. The vitamin has been used to treat a wide variety of conditions, which may or may not be related to inadequate intake. In some conditions use of vitamin B-6 supplements has been purely empirical; in other conditions there is a reasonable physiological or metabolic mechanism to explain why supplements of the vitamin many times greater than average requirements may have therapeutic uses. However, even in such conditions there is little evidence of efficacy from properly conducted controlled trials

Effects of a dietary excess of leucine on the metabolism of tryptophan in the rat: a mechanism for the pellagragenic action of leucine

In order to investigate the mechanism of the pellagragenic action of excess dietary leucine, rats were fed on diets providing a minimally-adequate amount of tryptophan, with no preformed niacin, with and without the addition of 15 g leucine/kg diet. This amount of leucine in the diet has been demonstrated previously to lead to depletion of blood and liver nicotinamide nucleotides. The metabolism of tryptophan was assessed by measurement of the production of 14CO2 after the administration of [methylene-14C]tryptophan to estimate the activity of kynureninase (L-kynurenine hydrolase, EC 3.7.1.3) and [benzene ring U-14C]tryptophan to estimate the activity of picolinate carboxylase (aminocarboxymuconate semialdehyde decarboxylase, EC 4.1.1.45). A dietary excess of leucine led to inhibition of kynureninase and increased the activity of picolinate carboxylase. Both of these effects would result in a reduction in the rate of metabolism of acroleylaminofumarate (aminocarboxymuconate semialdehyde) to quinolinic acid and hence to nicotinamide nucleotides. These two effects provide an explanation for the pellagragenic effect of a dietary excess of leucine in animals that are wholly or partly reliant on endogenous synthesis from tryptophan to meet their requirements for nicotinamide nucleotides, and presumably also explain the pellagragenic effect of a dietary excess of leucine in man

‘URS Campestre’ seedless orange: a new mutant with female sterility

Seedlessness in fruit is a trait that is much sought after by juice making industries. Close to the city of São Sebastião do Caí, in the state of Rio Grande do Sul (RS), Brazil, a new mutant orange originating from natural mutation was identified and selected as a seedless material. To determine the mechanisms involved in the absence of seeds, the reproductive structures of this new mutant by comparison with a Valencia sweet orange as control, a cultivar with a profusion of seeds, was analyzed in terms of meiotic behavior, meiotic index, pollen viability, in vitro germination, and ovule features to determine the grounds for seed absence. Other morphological analyzes allowed for visualizing the structures of normal appearance and size in both cultivars. Meiotic analysis identified chromosome normal pairing with a predominance of bivalents at diakinesis and metaphase 1. URS Campestre flowers at different developmental stages had anthers and ovaries whose dimensions are typical while pollen grain analysis pointed to a standard developmental pattern, normal meiosis, high viability (84 %) and elevated in vitro pollen tube germination rates (63 %). The cv. Valencia and URS Campestre ovules had a similar shape and morphology, sharing an anatropous orientation, and two integuments. In the internal ovule analyses of Valencia sweet oranges, normal embryo sac cells were identified: presence of one egg cell and two synergids, three antipodes and a bigger and central cell containing two polar nuclei. However, the analysis of ovules from URS Campestre reveals an apparent senescence or non-formation of an embryo sac, where only a few highly stained and collapsed cells could be identified. These results led to the conclusion that female sterility in URS Campestre, with a total absence of a female gametophyte, is the limiting factor for fertilization and seed production

VLT and NTT Observations of Two EIS Cluster Candidates. Detection of the Early-Type Galaxies Sequence at z~1

Optical data from the ESO VLT-UT1 Science Verification observations are combined with near-infrared data from SOFI at the NTT to obtain optical-infrared color-magnitude diagrams for the objects in the fields of two EIS cluster candidates. In both cases, evidence is found for a well-defined sequence of red galaxies that appear to be significantly more clustered than the background population. These results suggest that the two systems are real physical associations. The (R-Ks), (I-Ks) and (J-Ks) colors of the red sequences are used, in conjunction with similar data for spectroscopically confirmed clusters, to obtain redshift estimates of z ~ 0.9 and z ~ 1.0 for these two systems. These results make these EIS cluster candidates prime targets for follow-up spectroscopic observations to confirm their reality and to measure more accurately their redshift.Comment: 6 pages, 5 figures, to appear in Astronomy & Astrophysics (Special Letters Edition on "First Science with the VLT"

Uso de fosfato natural no cultivo de arroz, soja e milho em rotação, no sistema plantio direto.

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Monitoramento de cargas de produtos hortícolas no Brasil

No presente trabalho, são monitoradas as condições de temperatura de transporte e incidência de danos mecânicos de produtos frescos – sendo transportados em compartimentos de carga aberto ou fechada - em transporte local (região metropolitana de Porto Alegre) e de longa distância (viagens com distância maior que mil quilômetros) para obtenção de dados mais abrangentes e, com isso, auxiliar na busca por soluções tecnológicas para reduzir as imensas quantidades de produtos frescos desperdiçados. Com isto deverá haver uma redução na pressão de sistemas de produção em um ambiente em que se torna imprescindível preservar os recursos naturais enquanto há uma demanda crescente por diversidade e qualidade de produtos frescos. No estágio realizado de 1 de janeiro a 30 de março de 2017, com alguns dias esporádicos durante o ano de 2017 foram coletados dados de temperaturas nos compartimentos de carga de caminhões em várias regiões do Brasil. Foram averiguados dados de temperatura de caminhões da Silvestrin, empresa localizada em Farroupilha, mas com sedes nas CEASA de Porto Alegre e Brasília. Também foram coletados dados de agricultores de Vigia, localidade no interior de São Sebastião do Caí. Ocorreram saídas de campo para buscar e receber os sensores de temperatura que eram colocados junto aos produtos hortícolas no compartimento de carga. Os dados coletados eram transmitidos via USB para elaborar gráficos para melhor compreensão da variabilidade das temperaturas em planilha Excel. A partir das informações obtidas com os monitoramentos de carga é possível concluir que o uso combinado de tecnologias precisa estar aliado a uma adequada gestão de movimentação de cargas para abastecer mercados e, assim, contribuir para que ocorram menos perdas e desperdícios aliviando a enorme pressão sobre os recursos naturais e financeiros para atender o crescimento populacional

Inhibition of kynureninase (L-kynurenine hydrolase, EC 3 . 7. 1 . 3) by oestrone sulphate: an alternative explanation for abnormal results of tryptophan load tests in women receiving oestrogenic steroids

1. A partial purification of kynureninase (L-kynurenine hydrolase, EC 3 . 7. 1 . 3) from rat liver and a total resolution of the apoenzyme have been achieved. The hypothesis that conjugates of oestrogenic steroids compete with pyridoxal phosphate for the cofactor binding site of the enzyme, and so disturb tryptophan metabolism, leading to apparent vitamin B6 deficiency, has been tested. 2. Kynureninase from rat liver was partially purified, and the cofactor-free apoenzyme was prepared. Oestrone sulphate inhibited the enzyme uncompetitively with respect to pyridoxal phosphate, and competitively with respect to kynurenine, with a mean (+/- SE) inhibitor constant (Ki) of 82 +/- 6 microM. 3. The addition of a saturating concentration of pyridoxal phosphate to unfractionated liver homogenates led to an approximately fivefold increase in kynureninase activity, indicating the presence of a relatively large amount of apo-kynureninase in the tissue. 4. It is suggested that the abnormal results of tryptophan load tests in women receiving oestrogens are the result of inhibition of kynureninase by oestrogen conjugates, and that there is no evidence for oestrogen-induced vitamin B deficiency in such cases