Biomedical subjects

G Rivera

Publications and source records attributed to G Rivera.

At least 19 recordsLinked to original sources

PubMed2001

Dynamic study of homoleptic bimetallic platinum(II) complexes bridged by fluorinated benzenethiolates.

A variable-temperature (19)F NMR study of the homoleptic bimetallic anionic complexes X(2)[Pt(2)(mu-SC(6)F(5))(2)(SC(6)F(5))(4)] (X = K(+), 1a; Bu(4)N(+), 1b), X(2)[Pt(2)(mu-p-SC(6)HF(4))(2)(p-SC(6)HF(4))(4)] (X = K(+), 2a; Bu(4)N(+), 2b), and X(2)[Pt(2)(mu-p-SC(6)F(4)(CF(3)))(2)(p-SC(6)F(4)(CF(3)))(4)] (X = K(+), 3a; Bu(4)N(+), 3b) demonstrates the occurrence of dynamic processes that give rise to several stereoisomeric species in solution. Experimental evidence suggests that both inversion of configuration at the sulfur bridging atoms and hindered rotation about the carbon-sulfur bond are involved in generating the observed isomers. The solid-state X-ray diffraction structures of compounds 1b, 2b, and 3b show that all three complexes contain planar [Pt(2)(mu-S)(2)] rings with an anti configuration.

Journal Article↗

PubMed2001

Red wine raises plasma HDL and preserves long-chain polyunsaturated fatty acids in rat kidney and erythrocytes.

The effects of red wine and ethanol on plasma lipoproteins and the fatty acid composition of kidney lipids and erythrocytes phospholipids were studied. Lipid peroxidation is one of the main deleterious effects of oxidant attack on biomolecules, due to the disruption of the structural integrity of membranes. The vulnerability of the kidney to oxidative damage has been partly attributed to its high content of long-chain polyunsaturated fatty acids. Antioxidants, such as flavonoids, would be a means of reducing the risk of oxidative damage to membranes. Nutritional sources rich in antioxidants, including those provided by wine, are expected to attenuate the effects of oxidative challenges. Adult rats were fed red wine rich in flavonols, ethanol (125 ml/l), or alcohol-free red wine. The control group drank water. After 10 weeks, blood samples served to measure plasma lipoproteins and antioxidant capacity. Kidney lipids and erythrocyte phospholipids were extracted. The samples were assayed by GLC. Energy intake did not differ between all the groups, but the weight gain of the ethanol group was less than the other three groups. Blood HDL and triacylglycerols were increased by both ethanol and red wine. Ethanol decreased arachidonic and docosahexaenoic acids in both kidney lipids and erythrocyte phospholipids, as compared with either water, red wine or alcohol-free red wine groups. These results indicate that non-alcoholic components of red wine could contribute to avoiding the unfavourable effects of ethanol on plasma lipoproteins, kidney lipids and membrane erythrocyte phospholipids.

Animals↗

PubMed2001

Induction of flowering in tropical trees by a 30-min reduction in photoperiod: evidence from field observations and herbarium specimens.

During the late rainy season in October 1997 we observed. over a range of >100 km, the highly synchronous emergence of flower buds in several deciduous tree species of the semi-deciduous tropical forest in Guanacaste, Costa Rica. Synchronous flowering soon after the rapid decline in day length around the September equinox and in the absence of any notable climatic cues suggested flower induction by declining photoperiod. By combining field observations and the analysis of flowering herbarium collections, we established highly synchronous flowering periods with low interannual and latitudinal variation predicted for photoperiodic flower induction for more than 25 tree species and a few herbs. We describe morphogenetic changes at the shoot apex of three species during flower induction and the suppression and induction of flowering in several herbaceous species by experimental daylight extension. The combined observations provide strong, mainly indirect evidence for photoperiodic induction of flowering in many tropical tree species. At low latitudes with annual variation in day length of 1 hour, flower induction must be caused by a decline in photoperiod of 30 min or less. This is the first report of photoperiodic control of flowering in trees.

Costa Rica↗

PubMed2001

Photoperiodic control of seasonal development and dormancy in tropical stem-succulent trees.

Tropical stem-succulent trees store large quantities of water in their trunks yet remain leafless during the early and mid dry season. In contrast to most other tropical trees, bud break of vegetative buds is not induced in fully hydrated stem succulents between the winter solstice and the spring equinox by leaf abscission, abnormal rain showers or irrigation. Vegetative buds of leafless trees are therefore in a state of endo-dormancy similar to that of temperate perennial plants during early winter. Highly synchronous bud break regularly occurs soon after the spring equinox, often weeks before the first rainfalls of the wet season. These observations suggested that endo-dormancy and bud break might be induced by declining and increasing photoperiods after the autumn and spring equinoxes, respectively. In phenological field observations, we confirmed highly synchronous bud break after the spring equinox in many trees of five stem-succulent species in the northern and southern hemispheres. Shoot growth of potted saplings of Plumeria rubra L. was arrested by a decline in day length below 12 h after the autumn equinox, but continued in saplings maintained in a 13-h photoperiod. Conversely, exposure to a 13-h photoperiod induced bud break of dormant apical buds in saplings and cuttings in January, whereas plants maintained in the natural day length of < 11.7 h remained dormant. Photoperiodic control of endo-dormancy of vegetative buds in stem succulents is thus supported by field observations and experimental variation of the photoperiod. At low latitudes, where annual variation of day length is less than 1 h, bud dormancy is induced and broken by variations in photoperiod of less than 30 min.

Photoperiod↗

PubMed2000

Magnetic resonance arthrography of the temporomandibular joint.

PURPOSE: This study evaluated the usefulness of magnetic resonance arthrography (MRAr) in imaging the pathologic temporomandibular joint (TMJ). PATIENTS AND METHODS: Thirteen TMJs of 11 patients with chronic TMJ pain and disability were examined with MRAr. T1-weighted and T2-weighted first spin-echo sequence with fat suppression images were obtained after the intra-articular injection of gadopentetate dimeglumine. RESULTS: The disc, the posterior attachment, and the presence of perforations and adhesions were evaluated in each image. All of these anatomic and pathologic structures were clearly detected. CONCLUSION: MRAr appears to be a promising imaging modality in detecting adhesions and perforations in the TMJ. The MRAr findings simplified the decision of whether a patient should undergo surgery.

Adult↗

PubMed2000

Gender differences in clinical outcome after coronary stenting.

OBJECTIVE: The purpose of this study was to determine the effect of gender differences in the clinical outcome of women and men submitted to coronary stenting at our institution. BACKGROUND: Studies regarding gender differences in outcome after invasive coronary interventions have revealed conflicting data regarding risk for complications. Some studies have pointed to female gender as a predictor of mortality and complications after those procedures. To our knowledge no such evaluation has been performed in our country. METHODS: We reviewed the medical records, cardiac catheterization and procedural data of 205 men and 122 women referred to our section that underwent coronary stenting at the Cardiovascular Center of Puerto Rico and the Caribbean from July 1, 1998 to March 30, 1999. The clinical and procedural characteristics and the immediate procedure-related complications were analyzed. Clinical events during the six-month period after the procedure were evaluated in patients that returned for follow-up to the section. Student's t-test or Mann-Whitney-Wilcoxon, when appropriate, was used to compare continuous data. The chi-square test or Fisher's exact test, was employed to compare categorical data. RESULTS: The initial procedural success and the frequency of early complications were comparable to those informed in the medical literature and not statistically significant between genders. The only statistically significant gender differences in outcome occurred in men who had higher re-hospitalization and re-intervention rates in the six-month period after the procedure. A lower mean ejection fraction and higher previous history of myocardial infarction and cigarette smoking in this group could have been related to the higher complication rate. CONCLUSION: Although the sample examined is small, its findings point to the need of a larger prospective study to further explore the possibility that the previously reported differences in outcome in men and women submitted to interventional procedures would have a stronger relation to clinical factors than to the direct effect of gender.

Cardiac Surgical Procedures↗

PubMed1999

Vibrios associated with Litopenaeus vannamei larvae, postlarvae, broodstock, and hatchery probionts.

Several bacteriological surveys were performed from 1994 to 1996 at different Litopenaeus vannamei hatcheries (in Ecuador) and shrimp farms (in Mexico). Samples were taken from routine productions of healthy and diseased L. vannamei larvae, postlarvae, and their culture environment and from healthy and diseased juveniles and broodstock. In Ecuador, the dominant bacterial flora associated with shrimp larvae showing symptoms of zoea 2 syndrome, mysis mold syndrome, and bolitas syndrome has been determined. Strains were characterized by Biolog metabolic fingerprinting and identified by comparison to a database of 850 Vibrio type and reference strains. A selection of strains was further genotypically fine typed by AFLP. Vibrio alginolyticus is predominantly present in all larval stages and is associated with healthy nauplius and zoea stages. AFLP genetic fingerprinting shows high genetic heterogeneity among V. alginolyticus strains, and the results suggest that putative probiotic and pathogenic strains each have specific genotypes. V. alginolyticus was found to be associated with larvae with the zoea 2 syndrome and the mysis mold syndrome, while different Vibrio species (V. alginolyticus and V. harveyi) are associated with the bolitas syndrome. V. harveyi is associated with diseased postlarvae, juveniles, and broodstock. The identities of the strains identified as V. harveyi by the Biolog system could not be unambiguously confirmed by AFLP genomic fingerprinting. Vibrio strain STD3-988 and one unidentified strain (STD3-959) are suspected pathogens of only juvenile and adult stages. V. parahaemolyticus, Photobacterium damselae, and V. mimicus are associated with juvenile and adult stages.

Animals↗

PubMed1996

National vitamin A survey in Panama.

The prevalence of vitamin A deficiency in a nationally representative sample of children 12-59 months old in Panama was assessed using serum retinol levels and dietary indicators. The median serum retinol level found was 1.27 +/- 0.42 mumol/L (38 micrograms/dL); 6.0% of the study sample providing adequate blood specimens had levels below 0.7 mumol/L (20 micrograms/dL), indicating deficient vitamin A intake. The Panama City Metropolitan Area and the country's western region had the highest prevalences of low serum retinol levels (below 0.7 mumol/L in 9% and 6% of the study children, respectively), as compared to overall prevalences of 5% in the two other regions studied. Low serum retinol levels were significantly more prevalent among Indians in the study group (primarily Guaymí Indians) than among non-Indians (13% versus 5%). Dietary information provided by the study children's mothers showed that high risk of inadequate dietary vitamin A intake closely paralleled low serum retinol levels; specifically, the highest prevalence of dietary inadequacy was found in the western region, especially among the Indians. The Panamanian Government is currently increasing distribution of high-dose vitamin A capsules to Indian preschoolers in Chiriquí and Bocas del Toro Provinces.

Child Nutrition Disorders↗

PubMed1994

Pharmacokinetics of vincristine in children and adolescents with acute lymphocytic leukemia.

We studied the pharmacokinetics of vincristine in children with acute lymphocytic leukemia by means of a specific high-performance liquid chromatographic assay with ultraviolet and electrochemical detection and a limited sampling strategy. Our objectives were to characterize the disposition of vincristine in pediatric patients, to determine clinical, demographic, or biochemical variables related to variability in vincristine pharmacokinetic parameters, and to assess the relationship between pharmacokinetic parameters and vincristine neurotoxicity. Plasma samples were collected at 5 and 30 minutes, and 1, 3, and 24 hours after a rapid intravenous injection during 3 minutes. Vincristine-induced neurotoxicity was retrospectively evaluated by chart review. Pharmacokinetic studies were completed for 64 doses in 54 children between 2 months and 18 years of age (median, 4.3 years), including 2-month-old monozygous twin girls. Vincristine clearance, estimated by Bayesian methods, was highly variable, with a mean (SD) clearance of 19.9 (14.9) ml/min per kilogram or 482 (342) ml/min per square meter. Mean clearance for all subjects was faster than in published studies of adults, which may be related in part to the greater specificity of the assay used in our study, as well as to age-related differences in drug disposition. Vincristine-associated neurotoxicity was frequent but mild and was not predicted by vincristine systemic exposure; however, neurotoxicity may have been underestimated. Clearance in one patient who received concomitant treatment with pentobarbital exceeded the 75th percentile for all patients, and four of five patients receiving concomitant histamine2 antagonists had clearances below the 25th percentile for all subjects, suggesting that drugs that induce or inhibit hepatic cytochrome P-450 enzymes may affect vincristine disposition. Further studies are needed to identify the factors responsible for interpatient variability in vincristine disposition and to develop improved dosing guidelines.

Adolescent↗

PubMed1993

Treatment of CNS relapse in children with acute lymphoblastic leukemia: A Pediatric Oncology Group study.

PURPOSE: To assess the efficacy and toxicity of chemotherapy and cranial radiation for the treatment of children with acute lymphoblastic leukemia (ALL) following first isolated CNS relapse. PATIENTS AND METHODS: One hundred twenty children were treated on Pediatric Oncology Group (POG) protocol 8304. All children had received prophylactic CNS therapy during their initial treatment. The treatment protocol included a four-drug reinduction and six weekly doses of triple intrathecal therapy (TIT). Cranial radiation, 24 Gy, was followed by monthly TIT. Systemic consolidation and maintenance therapy included 6-week cycles of mercaptopurine/methotrexate (6MP/MTX) and vincristine/cyclophosphamide (VCR/CTX), with randomization to intervening pulses of prednisone/doxorubicin (PDN/DOX) or teniposide (VM26)/cytarabine (Ara-C) for a total of 88 weeks. RESULTS: All 120 patients achieved a second complete remission. There have been 61 protocol failures. Thirty-five patients had a bone marrow relapse, four with simultaneous CNS involvement and one with concurrent testicular leukemia. Thirteen patients had a second isolated CNS relapse, 10 a testicular relapse, and two relapsed in other sites. One patient died in remission. Overall event-free survival (EFS) at 4 years was 46% +/- 7%. The toxicity associated with this protocol was minimal except for leukoencephalopathy, which occurred in 20 (17%) patients. The treatment comparison between VM26/Ara-C or PDN/DOX pulses showed a trend toward superior EFS (P = .12) in favor of VM-26/Ara-C. CONCLUSION: To date, this represents the largest series of patients with ALL treated uniformly for an isolated CNS relapse. Since marrow relapse remains the primary site of failure, future protocols must intensify systemic therapy.

Adolescent↗

PubMed1993

Escalating teniposide systemic exposure to increase dose intensity for pediatric cancer patients.

PURPOSE: The primary objective for this study was to determine whether controlling pharmacokinetic variability, by designing patient-specific dosage regimens for teniposide using a Bayesian estimation control strategy, would permit an increase in dose intensity without increased toxicity. PATIENTS AND METHODS: Twenty patients with relapsed acute lymphocytic leukemia were given teniposide as part of their induction and maintenance therapy. Before beginning reinduction therapy, an intensive pharmacokinetic study was performed based on 12 measured teniposide plasma concentrations. Doses were determined to achieve a targeted systemic exposure defined by an area under the plasma concentration time curve (AUC) beginning at an AUC consistent with that predicted for a patient with average pharmacokinetic parameters receiving the currently accepted maximal-tolerated dose. The targeted systemic exposure was then escalated in increments of 25% in cohorts of at least three patients until unacceptable toxicity occurred. In 36 follow-up studies, when teniposide was administered during maintenance therapy, a Bayesian strategy based on only three or five measured drug concentrations was evaluated for precision and bias for achieving the targeted systemic exposure against the full pharmacokinetic study. RESULTS: Teniposide clearance varied over a fivefold range (3.7 to 21.6 mL/min/m2). With the use of the patient-specific dosage regimens, the intensity of systemic exposure was increased 50% (1,656 mumol.h v 1,060 mumol/L.h) over that previously possible with standard fixed doses, with no increase in acute, nonhematologic toxicity. Teniposide concentrations (n = 265) were well predicted (R2 = .82) with as few as three measured values from the initial study. CONCLUSION: Targeting systemic exposure is clinically feasible, precise, and allows increased dose intensity for teniposide without increased risk of acute, nonhematologic toxicity, when compared with fixed-dose regimens.

Adolescent↗

PubMed1992

The nutritional status of Guaymi Indians living in Chiriqui province, Republic of Panamá.

Guaymi Indian children have recently been identified as a population group who are at risk for vitamin A deficiency with numerous cases of xerophthalmia with ocular perforation being reported. A four-day parasitological and nutritional clinic based survey was conducted with 335 Guaymi women and children in the towns of San Felix and Alto Caballero to identify the prevalence of parasitic infections and factors associated with malnutrition. A subsample of 79 children, under 19 years of age, from independent families was constructed for the current analysis. The results of the study indicated that 20% of the children had a plasma vitamin A concentration less than 20 micrograms/dl. Significant associations were identified between ascariasis, age, a food diversity score and vitamin A concentrations. Other indicators of nutritional status were also negatively associated with intestinal parasitic infections, and a modernization index, using multivariate regression analysis. In conclusion, this study identified several factors associated with poor nutritional status that can be used by health officers to identify Guaymi children at risk for malnutrition.

Adolescent↗

PubMed1991

[The comparative treatment with lovastatin and bezafibrate of primary hypercholesterolemia. A randomized and double-blind trial].

The efficacy and tolerability of lovostatin (L) and bezafibrate (B) were compared in a total of 39 patients, 24 males and 15 females, 59 +/- 9 years old. Showing a total serum cholesterol superior to 250 mg/dl and total serum triglycerides inferior to 350 mg/dl, after 1 month on a low cholesterol diet and another on placebo, were eligible for participation. After randomization 19 treated with L started with 20 or 40 mg at night according to baseline cholesterol under or above 300 respectively and 20 with B received 200 mg tid. If after 6 weeks of therapy cholesterol remained above 200, the doses of L or matching placebo in those with B was double while dose of B or matching placebo remained constant. Cholesterol, triglycerides, LDL-cholesterol and HDL-cholesterol were determined using an enzymatic analytical method. Apolipoproteins were obtained by radial immunodiffusion. Routine hematological analysis and blood chemistry safety tests were performed at baseline and every 6 weeks during active treatment. The average most important results, after 12 weeks of treatment, comparing L vs B were: 1) cholesterol was reduced 26 vs 10% (p less than 0.001); 2) LDL-cholesterol decreased 35 vs 15% (p less than 0.001); 3) HDL-cholesterol increased 5 vs 19% (p = NS); 4) triglycerides diminished 15 vs 18% (p = NS). Three patients in L and 1 in B showed adverse events and two of them, one each group, were drop-out. In summary: a) L was more effective lowering total cholesterol and LDL-cholesterol; b) B was more potent decreasing triglycerides and increasing HDL-cholesterol; c) both drugs showed good tolerability.

Apolipoproteins A↗

PubMed1990

[Paratyphoid B fever in 2 areas of Santiago. An analysis of the epidemiological significance].

Salmonella isolates from 3920 patients with typhoid fever from 2 areas in Santiago were analyzed to determine the frequency of association with S paratyphi B infection. This was demonstrated in 18.8% of subjects in both areas, a figure significantly higher than the 8-10% previously reported. The association with S paratyphi B was higher for females, especially for the younger age group. These findings suggest an infectious agent-gender-age interaction which may explain the discrepancy with previously reported rates of infection. Their possible relation to the chronic salmonella carrier state and association with biliary tract lithiasis and cancer is discussed.

Adolescent↗

PubMed1988

Intestinal helminthiases in relation to the socioeconomic environment of Panamanian children.

A cross-sectional investigation was made into ascariasis and nutritional status in Panamanian preschool children from October 1983 to July 1984. Within this framework, an analysis was undertaken of possible relationships between a range of intestinal helminthiases and the socioeconomic status of the participants. Attention was paid to caregiver's education, parental occupation, family earnings, quality of housing and sanitation in the assessment of socioeconomic status. On this basis, strong associations were established between the socioeconomic status of the children and infection with Ascaris lumbricoides, Trichuris trichiura and hookworm. In general, the prevalence of single and multiple helminth infections was significantly higher in children living in housing made of wood or bamboo than in those living in housing made of concrete blocks. The same pattern applied to levels of sanitation. Ascaris lumbricoides occurred more frequently in children of mothers with the least formal education and in children living in relatively crowded conditions. Evidence was also obtained to indicate that the intensity of the intestinal helminth infections was greater in the children from the poorer environment. Since children from poorer socioeconomic conditions might be more exposed to infective stages than those from a better environment, the possible role of socioeconomic factors in contributing to the predisposition of some individuals to harbour large worm burdens of intestinal helminths was briefly discussed.

Ascariasis↗

PubMed1987

Multiple telomeric associations of a trisomic whole q arm of chromosome 1 in a child with acute lymphoblastic leukemia.

The results of cytogenetic analysis of bone marrow cells from a 13-year-old boy with acute lymphoblastic leukemia (ALL) are described. Initial analysis of aspirated bone marrow disclosed ALL FAB-L1 morphology, common (Ia+, cALLa+) immunophenotype and a complex abnormal karyotype. The majority of leukemic cells showed unbalanced translocations that resulted in complete trisomy of the long arm of chromosome #1 as the common denominator. The heterochromatic region of chromosome #1 (1qh) was associated with the telomeres of whole chromosomes #2, #13, and #16 in 28% of the 36 metaphases completely analyzed. Telomeric association is a very rare event and this is only the second known report of its occurrence associated with ALL wherein the 1qh region is attached to the telomeres of different chromosomes, resulting in trisomy of the whole 1q arm.

Adolescent↗

PubMed1987

Contributions of ascariasis to poor nutritional status in children from Chiriqui Province, Republic of Panama.

Relationships between ascariasis and lactose digestion and between ascariasis and food transit time from mouth to caecum were investigated in young children from Chiriqui Province, Republic of Panama. The breath hydrogen method was used in both studies. Ascaris-infected children showed a significantly poorer degree of lactose digestion following a test oral load than uninfected children. Recovery of the capacity of the children to digest lactose was still not fully complete for at least 3 weeks following anthelmintic treatment. On average, the mouth-to-caecum transit time was similar in infected and uninfected children, but among the Ascaris-infected children the transit time tended to be shorter in relation to the intensity of infection. Evidence from a cross-sectional survey indicated that ascariasis was significantly associated with reduced plasma vitamin A and carotenoid concentrations. This relationship remained after controlling for a range of socio-economic variables. Ascaris-infected children were frequently found to have lower haematocrits and blood haemoglobin concentrations than uninfected children, but these relationships could not be attributed to ascariasis alone.

Anthropometry↗

PubMed1987

Ocular relapse in the anterior chamber in childhood acute lymphoblastic leukemia.

We reviewed 11 cases of ocular relapse in the anterior chamber in children with acute lymphoblastic leukemia (ALL), representing 0.5% of all primary relapses seen at this center. Nine patients had hypopyon, and two had iris involvement only. Concomitant testicular relapse was present in two children and hematologic relapse in one. Ocular relapse occurred at 12 to 74 months (median, 36 months) from the data of initial diagnosis. Children who relapsed after therapy was discontinued did so within 1 year of completing therapy. Topical steroids and systemic chemotherapy were administered to all patients with ocular relapse; four also received radiation to the involved eye (600 to 1,050 cGy). Four children, each with a prolonged initial complete remission, remain free of disease for 15+, 32+, 34+, and 145+ months following anterior chamber relapse; three had received radiation therapy. Five patients died of recurrent leukemia, and two of infection while in remission. Aggressive retreatment appears warranted in cases of anterior chamber relapse of ALL, as some of these children may attain prolonged new remissions.

Adolescent↗