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N Torres

Publications and source records attributed to N Torres.

51 records · Page 3Linked to original sources
PubMed1991

Neutral amino acid transport into rat skeletal muscle: competition, adaptive regulation, and effects of insulin.

Amino acid (AA) transport systems A and L, which transfer preferentially small neutral AA (SNAA) and large neutral AA (LNAA), respectively, were studied in the isolated soleus muscle with the specific models, 2-(methylamino)isobutyrate (MeAIB) and 2-aminobicyclo[2,2,1]heptane-2-carboxylate (BCH). Affinity for MeAIB was greater than for BCH (Km = 3.2 +/- 0.2 and 8.7 +/- 0.2 mm, respectively). Rate of transport of MeAIB (Vmax = 104 +/- 3 pmol/microL/min) was slower than for BCH (970 +/- 12 pmol/microL/min), but accumulation was far more concentrative; transport of BCH, but not MeAIB, rapidly reached a steady-state level. MeAIB transport was reduced in the presence of SNAA; BCH transport was reduced to a lesser extent only by LNAA. Mixtures of AA at concentrations resembling those in plasmas of rats fed either a 6% or 50% casein diet reduced transport of MeAIB, whereas BCH transport was low only with the latter mixture. Only MeAIB transport was stimulated by insulin. Preincubation of muscles for 5 hours in a AA-free medium stimulated subsequent MeAIB uptake by about twofold to fourfold; this effect was suppressed by inhibitors of protein synthesis. Selective differences were thus observed in transport by skeletal muscle of model AA for the A and L systems: increased transport resulting from various stimuli was limited to the model for the A system, and transport of either model was depressed with mixtures containing physiological levels of AA. Changes in dietary protein or AA intake may thus alter transport of certain neutral AA into skeletal muscle via changes in plasma AA pools.

Amino Acids↗
PubMed1991

Cholinergic hyperactivity in the lateral septal area of spontaneously hypertensive rats: depressor effect of hemicholinium-3 and pirenzepine.

In the lateral septal area of spontaneously hypertensive rats, but not in Wistar-Kyoto rats, the selective M1 antagonist, pirenzepine, and the depletion of acetylcholine storage, by hemicholinium-3 (HC-3), decreased blood pressure. The selective M1 agonist McNeil-A-343, produced a pressor response only after treatment of the lateral septal area with HC-3 in spontaneously hypertensive rats. Carbachol, at doses that mainly affect M2 muscarinic receptors, caused no cardiovascular changes in either strain, pointing to the main intervention of the M1 subtype of muscarinic receptor in the hypertensive condition. In addition, increases in the density of binding sites for [3H]QNB and in Vmax of sodium-dependent, HC-3-inhibitable, high affinity uptake of choline were demonstrated, without significant changes of the activity of choline acetyltransferase in the lateral septal area of spontaneously hypertensive rats. These results suggest that a hyperactivity of the cholinergic system of this area could play a role in the development and/or maintenance of hypertension in spontaneously hypertensive rats.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1991

Glucocorticoid-induced hypertension in rats: role of the central muscarinic cholinergic system.

Betamethasone was administered on alternate days to rats, and the role of the central cholinergic system in the development of hypertension assessed. After 15 days of treatment the systolic blood pressure of treated rats was significantly higher than that of control rats. Peripheral administration of atropine but not of methyl atropine reduced systolic pressure in glucocorticoid-treated rats and had no effect in controls. Therefore, [3H]quinuclidinyl benzylate binding, sodium-dependent high-affinity choline uptake and choline acetyltransferase studies were performed in the septal area, anteroventrolateral medulla (AVLM), anterior hypothalamic preoptic area (AH/PO) and hypothalamus. The density of muscarinic receptors was increased in the hypothalamus and AVLM of treated rats without significant changes in affinity. Choline acetyltransferase activity significantly decreased in the AVLM and increased in the AH/PO. In addition, a decrease in the hypothalamus and an increase in the AH/PO of sodium-dependent high-affinity choline uptake was observed in glucocorticoid-treated rats. These results suggest the presence of an enhanced muscarinic cholinergic activity in several brain nuclei in rats with glucocorticoid-induced hypertension. This activation could be due to pre- and post-synaptic hypersensitivity.

Animals↗
PubMed1990

High branched-chain alpha-keto acid intake, branched-chain alpha-keto acid dehydrogenase activity, and plasma and brain amino acid and plasma keto acid concentrations in rats.

Diets containing high quantities of individual branched-chain alpha-keto acids (BCKAs) or a combination of BCKAs as used for treatment of renal disease were fed to rats. When the diet contained a single BCKA, its concentration was high in plasma and the concentration of its corresponding amino acid was high in plasma and brain. Liver BCKA dehydrogenase (BCKD) was 42% active in control rats. Consumption of diets containing 0.38 mol/kg diet of alpha-ketoisocaproate (KIC), alpha-keto-beta-methylvalerate (KMV), or alpha-ketoisovalerate (KIV) resulted in complete activation of liver BCKD. Consumption of the diet containing the combination of BCKAs increased basal BCKD activity of liver twofold. Muscle BCKD was activated after feeding the KIV diet (2-fold), the KIC diet (3-fold), and the KMV diet (15-fold). Total BCKD activity of liver and muscle was unaffected by dietary treatments. Activation of liver and muscle BCKD by dietary BCKA is consistent with their ability to inhibit BCKD kinase in vitro.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1988

Adenylate cyclase activity in a higher plant, alfalfa (Medicago sativa).

An adenylate cyclase activity in Medicago sativa L. (alfalfa) roots was partially characterized. The enzyme activity remains in the supernatant fluid after centrifugation at 105,000 g and shows in crude extracts an apparent Mr of about 84,000. The enzyme is active with Mg2+ and Ca2+ as bivalent cations, and is inhibited by EGTA and by chlorpromazine. Calmodulin from bovine brain or spinach leaves activates this adenylate cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1988

Some characteristics of threonine transport across the blood-brain barrier of the rat.

Threonine entry into brain is altered by diet-induced changes in concentrations of plasma amino acids, especially the small neutrals. To study this finding further, we compared effects of various amino acids (large and small neutrals, analogues, and transport models) on transport of threonine and phenylalanine across the blood-brain barrier. Threonine transport was saturable and was usually depressed more by natural large than small neutrals. Norvaline and 2-amino-n-butyrate (AABA) were stronger competitors than norleucine. 2-Aminobicyclo[2.2.1]heptane-2-carboxylate (BCH), a model in other preparations for the large neutral (L) system, and cysteine, a proposed model for the ASC system only in certain preparations, reduced threonine transport; 2-(methylamino)isobutyrate (MeAIB; a model for the A system for small neutrals) did not. Phenylalanine transport was most depressed by cold phenylalanine and other large neutrals; threonine and other small neutrals had little effect. Norleucine, but not AABA, was a strong competitor; BCH was more competitive than cysteine or MeAIB. Absence of sodium did not affect phenylalanine transport, but decreased threonine uptake by 25% (p less than 0.001). Our results with natural, analogue, and model amino acids, and especially with sodium, suggest that threonine, but not phenylalanine, may enter the brain partly by the sodium-dependent ASC system.

Amino Acids↗
PubMed1985

Effect of oral contraceptive use on the erythrocytic glutathione reductase and aspartate aminotransferase activities in women with or without clinical signs of vitamin deficiency.

The effect of the chronic use of combined oral contraceptives (OCs) on the "activity coefficients" (alpha = coenzyme-stimulated activity/basal activity) of erythrocytic glutathione reductase and aspartate aminotransferase was studied in 2 groups of 90 female volunteers each; 1 of the groups, from the state of Yucatan in southeast Mexico, presented clinical lesions of vitamin deficiency, while the other group, from Mexico City, did not have any clinical evidence of vitamin deficiency. One half of the women (45) in each group were chronic OC users and the other half were not. The results were analyzed comparing OC users with non-users in each location. For both glutathione reductase and aspartate aminotransferase, the Mexico City OC users had significantly higher (p 0.001) alpha values than nonusers, while in the Yucatan women, the alpha values were similarly high independent of OC use.

Americas↗
PubMed1981

Experimental Campylobacter diarrhea in chickens.

An animal model for Campylobacter fetus subsp. jejuni enteritis was developed in 3-day-old chickens. Diarrhea was induced in 88% (22 of 25) of chickens inoculated with 9 X 10(7) bacteria given orally. The mean incubation time was 45 h (range, 24 to 72 h). Considerable weight loss was observed in the experimental group compared with the control group. Ninety bacteria was the minimal infective dose capable of inducing diarrhea in 90% of the chickens. Overall mortality was 32% (8 of 25). Light microscopy, immunofluorescence, and electron microscopy of the gastrointestinal tract of serially sacrificed chickens were performed in control and experimental groups. A moderate infiltration of mononuclear cells was observed in ileum and cecum in the experimental group, with no disruption of intestinal mucosa. By immunofluorescence and electron microscopy, campylobacter was located within the epithelial cells and phagocytosed to a greater degree by mononuclear cells of the lamina propria.

Animals↗
PubMedDate not supplied

Effect of nutritional rehabilitation of undernourished rats on serum insulin-like growth factor (IGF)-I and IGF-binding proteins.

The aim of the present work was to study the effect of nutritional rehabilitation with different concentration of dietary protein (6, 18 or 50%) of previously undernourished rats on serum Insulin-like growth factor-I (IGF-I) and Insulin-like growth factor binding proteins levels (IGFBPs). Undernutrition was induced by feeding rats with 0.5% casein diet for 5 weeks. Over this period, growth, serum total proteins, IGF-I levels and IGFBP-3/IGFBP-2 ratio were significantly decreased compared to the group fed ad libitum 18% casein diet. Nutritional rehabilitation for 21 days with 6% casein diet did not change any of these parameters. Nutritional rehabilitation with 18 or 50% casein diet for one day did not initiate the restoration of serum IGF-I levels and IGFBP-3/IGFBP-2 ratio. However, after 10 days with 18 or 50% casein diets, there was an increase of 12 fold in IGF-I levels and 7 fold in the IGFBP-3/IGFBP-2 ratio. Finally, rehabilitation for 21 days with 18 or 50% casein diet produced an increase of 21 and 26 fold in IGF-I levels, and 6.1 and 14.5 fold in the IGFBP-3/IGFBP-2 ratio respectively. These results suggest that nutritional rehabilitation with 18% casein and above were more effective than 6% casein diets to reestablish body weight. Serum IGF-I and IGFBP-3 concentrations were sensitive indicators of the evolution of the nutritional status of the rats depending of the protein concentration in the diet in previously undernourished rats.

Animals↗
PubMedDate not supplied

[Homocysteine metabolism and risk of cardiovascular diseases: importance of the nutritional status on folic acid, vitamins B6 and B12].

Homocysteine is a thiol-containing amino acid derived from methionine metabolism that can be degraded through two enzymatic pathways: remethylation and trans-sulfuration. In remethylation, homocysteine regenerates methionine. In the trans-sulfuration pathway, homocysteine forms cysteine. Due to the rapid metabolic utilization, the plasma concentration of this amino acid is low. Homocysteine circulates as free thiol, homocystine, or bound to free cysteine or to cysteine residues of proteins. Genetic defects of some enzymes in the homocysteine metabolism, or nutritional deficiencies of folic acid, vitamin B6 and B12 lead to an increase in homocysteine plasma concentration and is associated to an increment in cardiovascular diseases. On the basis of clinical and epidemiological studies, homocysteine plasma concentration is considered to be an independent risk factor for the development of atherothrombotic and cardiovascular diseases. The present review describes the homocysteine metabolism, the epidemiological evidence showing the association between homocysteine and the incidence of cardiovascular diseases. The mechanisms by which homocysteine produces vascular damage are indicated. Finally, some recommendations are given for the nutritional therapy of patients with hyperhomocysteinemia.

Arteriosclerosis↗
PubMedDate not supplied

Hepatic phenylalanine-hydroxylase and tyrosine-aminotransferase mRNA levels in rats adapted to diets with different concentrations of protein.

The effect of dietary protein concentrations on the hepatic expression of phenylalanine hydroxylase (PAH) and tyrosine aminotransferase (TAT) mRNA concentrations was studied in rats adapted to consume diets (18 or 50% casein) in a restricted schedule of 7 h (0900 to 1600) for 5 days. After 6 hours of feeding, TAT mRNA concentrations of rats adapted to 18% casein diet and fed acutely 6, 18 and 50% casein diet were 0.15, 0.84 and 5.08 fold respectively higher than mRNA concentrations of rats before feeding. After 17 hours of fasting, TAT mRNA concentrations of rats previously fed 6, 18 or 50% casein diet were -0.45, 1.76 and 9.11 fold respectively higher than mRNA concentrations of rats before they were fed. PAH mRNA concentrations showed a similar pattern. There was a -0.68, 1.63 and 2.5 fold rise of PAH mRNA concentrations in rats fed 6,18 and 50% casein diet during the feeding period, and -0.86, 2.32 and 9.33 fold rise after 17 hours of fasting. TAT and PAH mRNA concentrations of rats adapted to consume 50% casein diet and then changed to 6% or kept on the 50% casein diet showed a maximum peak 6 hours after the rats began to consume the diet; however, they decreased 5 hours after fasting. These results suggest that increasing concentrations of protein in the diet were able to increase the concentration of TAT and PAH mRNA, possibly in order to eliminate the excess of amino acids consumed. The concentration of TAT and PAH mRNA depended more on the protein content of the diet to which the rats were previously adapted.

Animals↗
PubMedDate not supplied

[Free amino acids in plasma and milk of mexican rural lactating women].

OBJECTIVE: To determine the free amino acid pool in plasma and milk in Mexican rural lactating women. METHODS: Twenty-eight women with an age 24 +/- 5.0 (+/- SD) years, weight 50 +/- 4.9 kg and height 148 +/- 4.8 cm were studied under metabolic balance conditions. Subjects were divided into five groups (three groups of lactation at 1st, 3rd and 6th month, one post-weaning group and a control group of non pregnant, non lactating women). Amino acid analyses of the diet and of plasma and milk samples were performed using an automated amino acid analyzer. RESULTS: Differences were observed between the lactation groups and the other groups: aspartate increased at the 6th month (p < 0.05) while leucine, valine and isoleucine declined in the 3rd month (p < 0.05). In milk, valine, proline and taurine decreased at 6 months (p < 0.05), while serine and threonine raised at 3 months. Plasma levels were > 4 fold greater than milk levels for branched chain amino acids and for the basic, aromatic and neutral amino acids. In contrast, glutamate was 40 fold higher in milk than plasma and it was the predominant amino acid in the free pool of milk. CONCLUSIONS: Our results suggest that the metabolic use of amino acids and the presence of specific amino acid transport systems during lactation, contribute to specific concentrations of free amino acids in milk that were not associated with the pool of free amino acids in plasma.

Adult↗