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Biomedical subjects

Juan Rivera

Publications and source records attributed to Juan Rivera.

50 records · Page 3Linked to original sources
PubMed2003

Iron supplementation improves progressive fatigue resistance during dynamic knee extensor exercise in iron-depleted, nonanemic women.

BACKGROUND: Tissue iron depletion may negatively affect endurance performance and muscle fatigability. OBJECTIVE: We investigated tissue-level iron depletion and progressive fatigue of the quadriceps during dynamic knee-extension exercise in young women. DESIGN: Twenty iron-depleted (serum ferritin < 20 micro g/L), nonanemic (hemoglobin > 110 g/L) women (macro x +/- SEM age: 29.1 +/- 1.2 y) received iron (iron group) or placebo (placebo group) for 6 wk in a randomized, double-blind trial (n = 10 per group). A protocol integrating 2-3-s maximal voluntary static contractions (MVCs) with dynamic knee extensions was used to assess fatigue. RESULTS: No significant differences between the groups in baseline iron status, MVC at rest, or MVC at the end of the protocol were observed. After treatment, serum iron and transferrin saturation increased significantly in the iron group (P = 0.02 and P = 0.03, respectively). Serum transferrin receptor concentrations increased significantly in the placebo group (P < 0.01) but not in the iron group. After treatment, the rate of decrease in MVC was attenuated in the iron group but not in the placebo group (P = 0.01). In the iron group, MVC at the sixth minute of the fatigue protocol and MVC at the end of the protocol were approximately 15% (P = 0.04) and approximately 27% higher (P < 0.01), respectively, after treatment. These improvements were not related to changes in iron-status indexes or tissue iron stores, although power was low (< 0.50) to detect these relations. CONCLUSIONS: Iron supplementation was associated with a significant improvement in muscle fatigability. Interpretation regarding the direct role of tissue iron status is limited by the study's low power to detect relations between tissue iron improvement and decreased muscle fatigue.

Adolescent↗
PubMed2003

Multiple micronutrient supplementation during pregnancy does not lead to greater infant birth size than does iron-only supplementation: a randomized controlled trial in a semirural community in Mexico.

BACKGROUND: Little is known about the benefits of prenatal multivitamin and mineral supplements in reducing low birth weight. OBJECTIVE: We conducted a randomized, double-blind clinical trial in semirural Mexico to compare the effects of multiple micronutrient (MM) supplements with those of iron supplements during pregnancy on birth size. DESIGN: Pregnant women (n = 873) were recruited before 13 wk of gestation and received supplements 6 d/wk at home, as well as routine antenatal care, until delivery. Both supplements contained 60 mg Fe, but the MM group also received 1-1.5 times the recommended dietary allowances of several micronutrients. RESULTS: At recruitment, the women in the 2 groups were not significantly different in age, parity, economic status, height, or hemoglobin concentration but differed significantly in marital status (4.6% and 2.0% of women in the MM and iron-only groups, respectively, were single mothers) and mean (+/- SD) body mass index (in kg/m(2); 24.6 +/- 4.3 and 23.8 +/- 3.9 in the iron-only and MM groups, respectively). Losses to follow-up (25%) and compliance (95%) did not differ significantly between the groups. In intent-to-treat analyses (MM group: n = 323; iron-only group: n = 322), mean (+/- SD) birth weight (2.981 +/- 0.391 and 2.977 +/- 0.393 kg in the MM and iron-only groups, respectively) and birth length (48.61 +/- 1.82 and 48.66 +/- 1.83 cm in the MM and iron-only groups, respectively) did not differ significantly between the groups. CONCLUSION: These findings suggest that MM supplementation during pregnancy does not lead to greater infant birth size than does iron-only supplementation.

Adult↗
PubMed2003

[Factors associated with physical activity among Mexican women of childbearing age].

OBJECTIVE: To document the practice of light and heavy physical activities, especially sports and exercise, among women from 12 to 49 years old in Mexico, and to evaluate the association that that has with some sociodemographic characteristics. METHODS: A sample of 2 367 women 12 to 49 years old living in Mexico in 1999 was studied through secondary analysis of data from Mexico's 1999 National Nutrition Survey (Encuesta Nacional de Nutrición). The Survey used a clustered stratified multistage sampling scheme, with a final sample of 21 000 homes in the entire country. A questionnaire was used to evaluate the time that the women spent on various forms of physical activity, with the activity measured on a scoring scale in terms of metabolic equivalents (METs). The dependent variables in the study were the time spent on heavy physical activities (those that require an energy expenditure of at least 5 METs/hour) and the time devoted to light or sedentary activities (such as sitting while on the job or elsewhere; watching television, a video, a movie, or a theater presentation; or sleeping). The independent variables were age, schooling, parity, region of the country, area of residence (urban or rural), socioeconomic level (measured through an index prepared based on housing conditions and household possessions), and marital status. The association between the independent variables and practicing sports was evaluated, and gross odds ratios (ORs) were calculated, with 95% confidence intervals (CIs). In order to identify the association between practicing sports and the independent variables a logistic regression model was used, adjusted for the effects of possible confounding variables. Adjustments were also made in the probability of a woman's being selected for the sample, using a weighting factor. In addition, adjustments were made to control for the design effect produced by the grouping of the observations in the sample, using the "svy" complex-samples routine of the Stata version 7.0 statistical analysis computer software. RESULTS: The 2 367 women whose information was analyzed spent an average of 0.08 hours per day practicing sports and 1.25 hours per day on heavy physical activities. Only 16% of the women reported that they regularly practiced some sport. After adjusting for all the independent variables, the women older than 30 years had a lower OR of practicing sports in comparison to women who were 20 years of age or less (OR = 0.53; 95% CI: 0.33 to 0.84), as was also true for women 21-30 years old (OR = 0.35; 95% CI: 0.23 to 0.54). Having the highest level of schooling and not having had children were both directly associated with practicing a sport. While the area of residence (urban or rural), marital status, and socioeconomic level showed differences among the groups, such differences were not significant after adjusting for the other study variables. In terms of physical activity measured in METs, the time spent on sports made up 10% of the total for heavy activity and 0.7% of the overall total. In terms of the possibility of being among the 10% of the women who expended the fewest METs per day, that was more likely for women under 21 years of age than it was for women 31 or older, and it was also more likely for women who had a primary level of schooling than for women with a secondary education. CONCLUSIONS: This study showed that practicing sports is not a frequent form of physical activity among women of childbearing age in Mexico, especially those who are over 20 years of age and those with a low level of schooling. This situation could contribute to increases in the prevalence of obesity and chronic diseases.

Adolescent↗
PubMed2003

[Clinical study of measure of parasitemia in patients infected with Trypanosoma cruzi in Atacama, Chile].

BACKGROUND: Trypanosoma cruzi infection is endemic in Northern/Central Chile. AIM: To perform a clinical assessment of patients infected with Trypanosoma cruzi. PATIENTS AND METHODS: Two hundred sixty three subjects with a positive serology for Trypanosoma cruzi, were invited by mail to a clinical assessment in a Regional Hospital. In a subsample of these, a polymerase chain reaction for Trypanosoma cruzi, was done. RESULTS: Of all the invited subjects, 183 responded and were assessed at the hospital. Of these, 60 had cardiac affections, 52 had colon problems and 17, esophageal disease. Seventy four were asymptomatic. Of the 64 patients in whom polymerase chain reaction was done, 35 had a positive result. CONCLUSIONS: A high percentage of subjects infected with Trypanosoma cruzi, had clinical consequences of the infection. Polymerase chain reaction showed persistency of the parasite in more than half of the infected patients.

Adult↗
PubMed2002

Fyn kinase initiates complementary signals required for IgE-dependent mast cell degranulation.

Fc epsilon RI activation of mast cells is thought to involve Lyn and Syk kinases proximal to the receptor and the signaling complex organized by the linker for activation of T cells (LAT). We report here that Fc epsilon RI also uses a Fyn kinase-dependent pathway that does not require Lyn kinase or the adapter LAT for its initiation, but is necessary for mast cell degranulation. Lyn-deficiency enhanced Fyn-dependent signals and degranulation, but inhibited the calcium response. Fyn-deficiency impaired degranulation, whereas Lyn-mediated signaling and calcium was normal. Thus, Fc epsilon RI-dependent mast cell degranulation involves cross-talk between Fyn and Lyn kinases.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Vav1 is a component of transcriptionally active complexes.

The importance of the hematopoietic protooncogene Vav1 in immune cell function is widely recognized, although its regulatory mechanisms are not completely understood. Here, we examined whether Vav1 has a nuclear function, as past studies have reported its nuclear localization. Our findings provide a definitive demonstration of Vav1 nuclear localization in a receptor stimulation-dependent manner and reveal a critical role for the COOH-terminal Src homology 3 (SH3) domain and a nuclear localization sequence within the pleckstrin homology domain. Analysis of DNA-bound transcription factor complexes revealed nuclear Vav1 as an integral component of transcriptionally active nuclear factor of activated T cells (NFAT)- and nuclear factor (NF)kappaB-like complexes, and the COOH-terminal SH3 domain as being critical in their formation. Thus, we describe a novel nuclear role for Vav1 as a component and facilitator of NFAT and NFkappaB-like transcriptional activity.

Active Transport, Cell Nucleus↗
PubMed2002

Macromolecular protein signaling complexes and mast cell responses: a view of the organization of IgE-dependent mast cell signaling.

The generation of signals following engagement of cell surface receptors is an ordered process that requires tight regulation as spurious signals could result in unwanted, and possibly deleterious, cellular responses. Like other cell surface receptors, stimulation of a mast cell via the high affinity IgE receptor (FcepsilonRI) causes multiple biochemical events that ultimately result in cell activation and effector responses. Recently, our knowledge of how these events are ordered has increased. We now have identified some of the molecules involved, how they are organized into macromolecular complexes by FcepsilonRI stimulation, and the role of some of the constituents of these macromolecular signaling complexes in mast cell effector responses. In brief, we review the knowledge on macromolecular signaling complexes used by FcepsilonRI in mast cell activation and provide our view on the regulation of signal generation and its effect on mast cell activation.

Animals↗
PubMed2002

SNAREs and associated regulators in the control of exocytosis in the RBL-2H3 mast cell line.

Mast cells participate in inflammation and allergies by releasing biologically active mediators stored in numerous cytoplasmic granules. Degranulation is tightly controlled and requires activation of cell surface receptors, such as the high affinity IgE receptor (FcepsilonRI). Here, we discuss some of the key components of the molecular machinery that regulates the final steps of fusion between the granular and plasma membrane based on results obtained with the rat mast cell line RBL-2H3. We emphasize the role of soluble N-ethylmaleimide attachment protein receptors (SNAREs) proteins such as syntaxin 4 that can promote membrane fusion through formation of a stable complex with SNAP-23. We also highlight the role of a Ser/Thr kinase found to be associated with Rab3D, a negative regulator of degranulation. Associated kinase activity, which diminishes after stimulation as a consequence of intracellular calcium increases, specifically phosphorylates syntaxin 4 thereby affecting its capacity to bind to its t-SNARE partner SNAP-23. Our results suggest a new way of how Rab3 GTPases may intersect with the function of SNAREs thought to be universal mediators of membrane fusion.

Animals↗
PubMed2002

Molecular adapters in Fc(epsilon)RI signaling and the allergic response.

IgE-dependent activation of mast cells is central to the allergic response. The engagement of IgE-occupied receptors initiates a series of molecular events that cause the release of preformed, and de novo synthesis of, allergic mediators. Recent investigations demonstrate a critical role for non-enzymatic proteins that facilitate the activation and coordination of biochemical signals required for mast cell activation. Among these LAT, SLP-76 and Gab2 are critically important as adapters that facilitate events initiated by IgE receptor-dependent activation of Src family protein tyrosine kinases, Lyn and Fyn. An evaluation of the role of these adapters points to complementary but independent steps in early signaling and the possibility that preference for one or another adaptor complex may result in selective mast cell responses.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Effect of supplemental zinc on the growth and serum zinc concentrations of prepubertal children: a meta-analysis of randomized controlled trials.

BACKGROUND: Multiple studies have been carried out to assess the effect of zinc supplementation on children's growth. The results of these studies are inconsistent, and the factors responsible for these varied outcomes are unknown. OBJECTIVE: Meta-analyses of randomized controlled intervention trials were therefore completed to assess the effect of zinc supplementation on the physical growth and serum zinc concentrations of prepubertal children. DESIGN: A total of 33 acceptable studies with appropriate data were identified by MEDLINE (National Library of Medicine, Bethesda, MD) searches and other methods. Weighted mean effect sizes (expressed in SD units) were calculated for changes in height, weight, weight-for-height, and serum zinc concentration by using random-effects models; factors associated with effect sizes were explored by meta-regression techniques. RESULTS: Zinc supplementation produced highly significant, positive responses in height and weight increments, with effect sizes of 0.350 (95% CI: 0.189, 0.511) and 0.309 (0.178, 0.439), respectively. There was no significant effect of zinc on weight-for-height indexes [weighted mean effect size: -0.018 (-0.132, 0.097)]. Zinc supplementation caused a large increase in the children's serum zinc concentrations, with an effect size of 0.820 (0.499, 1.14). Growth responses were greater in children with low initial weight-for-age z scores and in those aged >6 mo with low initial height-for-age z scores. CONCLUSIONS: Interventions to improve children's zinc nutriture should be considered in populations at risk of zinc deficiency, especially where there are elevated rates of underweight or stunting. The population mean serum zinc concentration is a useful indicator of the successful delivery and absorption of zinc supplements in children.

Adolescent↗
PubMedDate not supplied

[ESOPHAGEAL STENOSIS IN CHILDREN: MEDICAL TREATMENT EXPERIENCE]

We present a retrospective evaluation of our experience in the period that goes from January 1992 to December 1998, clinical records of 58 patients ages from 2 months old to 15 years, male and female, who were treated at the GI service of Instituto de Salud del Ni o, were reviewed. All of them had esophageal stenosis and were included in the Esophageal Dilatation Program with Savary-Gilliard bougies. The causes of Esophageal Stenosis in the study were: Caustic agents 37.9%, gastro esophageal reflux (GER) 20.7%, surgery sequela 19.0%, related to esophageal esclerotherapy 12.1%, foreign body itself or maneuvers to retrieve them 8.6%, stomach adenocarcinoma invading the esophagus. Patients were classified in three groups: Group 1: stenosis due to caustic agents Group 2: stenosis due to GER Group 3: The remaining causes mentioned above., In each the following was calculated: the arithmetical media, the range of dilatations sessions and the total number of them. The higher figures took place in group 1. So we conclude that the number of sessions is directly related with the cause of the stenosis, requiring more number of dilatations to get a better response. Finally the response to treatment is evaluated considering a good response in 72.4%. A mild response in 15.5% and therapeutic failure in 12.1% of patients. The rate of complications was 10.3 per patient and 1.1 in relation to the total number of dilatation sessions. The main complications were: gastric perforation, duodenal perforation, pneumomediastinum, esophago-tracheal fistulae andi pseudodiverticulum formation, with resolution as seen in posterior controls. These complications occured after the proceeding took place. The treatment was installed according to each case. The patients with duodenal perforation died. We conclude that esophageal dilatations in infants with esophageal stenosis, of different ethiology, are secure and efficient.

Journal Article↗
PubMedDate not supplied

[FULMINANT HEPATIC FAILURE IN CHILDREN]

This study describes the etiology, clinical and laboratory characteristics of Fulminant Hepatic Failure in a pediatric population of 29 patients, of the Instituto Nacional del Niño, Lima, Peru. In eleven (11) of them, the etiology could not be established. HAV wasthe most frequent etiology, with 8 patients (44.4%) followed by inorganic phosphorus poisoning with 5 patients (27.7%). The mean age was 5 years and 4 months; encephalopathy followed by vomiting were the main symptoms and/or signs prompting the admittance of the children. The duration of the illness was 14.6 days and the time between the appearance of jaundice and the onset of encephalopathy was 6.65 days, the lesser the time the poorer the prognosis. The most frequent symptom in the physical exam was hepatomegaly followed by jaundice and encephalopathy. During its evolution all patients showed signs of encephalopathy and jaundice. The short protrombine time and the high rate of transaminases correlated with an improved prognosis and the Aspartate transaminase and bilirrubines were higher in the infectious causes. The mortality rate was 69%. The most frequent complication was upper gastro-intestinal bleeding, continued by hydroelectrolyte imbalance.

Journal Article↗
PubMedDate not supplied

[Congenital bronchobiliary fistula detected by cholescintigraphy].

A case of a six-year-old female patient diagnosed with congenital bronchobiliary fistula is presented. Only 20 cases have been reported in the literature of this disease in this institution. The patient showed signs and symptoms of a respiratory illness from birth that complicated progressively. She was submitted to multiple imaging studies like chest X rays, CT, ultrasound and Tc-99m HIDA cholescintigraphy. This procedure confirmed the presence of a bronchobiliary fistula that was corrected by surgery, with subsequent improvement of clinical symptoms.

Bile↗