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Biomedical subjects

A Rivera

Publications and source records attributed to A Rivera.

At least 73 records · Page 4Linked to original sources
PubMed1996

Elevated lymphocyte cytosolic calcium in a subgroup of essential hypertensive subjects.

Abnormalities of intracellular calcium homeostasis and sodium-proton exchange have been implicated in the pathophysiology of essential hypertension. To further define the nature of cytosolic calcium abnormalities and whether they relate to increased sodium-proton exchange in hypertension, we have studied peripheral lymphocytes from normotensive and hypertensive subjects. Lymphocyte cytosolic calcium was significantly increased (P < .01) in hypertensive compared with normotensive subjects while consuming a high salt diet. Using maximum likelihood analysis, we found that cytosolic calcium levels in our study population were not normally distributed and observed three modes (P < .02). The means of the first mode and the two upper modes were separated (+/-2 SD) at a cytosolic calcium level of 120 nmol/L. We conducted further analysis in the subgroups with cytosolic calcium levels > 120 nmol/L or < 120 nmol/L. The majority of the normotensive subjects (86%) and half of the hypertensive subjects (52%) had levels < 120 nmol/L. Clinical characteristics of the two subgroups did not differ. Subjects with levels < 120 nmol/L had a rise in cytosolic calcium when changed to a low salt diet; those with levels > 120 nmol/L did not show a change in cytosolic calcium but their blood pressure fell significantly with salt restriction. Hypertensive subjects also had increased sodium-proton exchange activity compared with normotensive subjects when both groups were studied in a high salt balance. A positive correlation between sodium-proton exchange and cytosolic calcium was observed in subjects with levels < 120 nmol/L. There was insufficient power to draw conclusions on this relationship in subjects with levels > 120 nmol/L. Thus, many hypertensive subjects have increased cytosolic calcium, but this abnormality is not associated with sodium-proton exchange activity in all individuals. The salt-induced change in cytosolic calcium in subjects with levels < 120 nmol/L and its link to sodium-proton exchange suggest regulation by factors involved in salt-volume homeostasis. Individuals with cytosolic calcium > 120 nmol/L, most of whom were hypertensive, may have abnormalities in this regulation, contributing to hypertension.

Adult↗
PubMed1996

A murine model for genetic manipulation of the T cell compartment.

The expression of exogenous genes in long-lived primary T cells is potentially beneficial for the treatment of various diseases including cancer, AIDS, genetic defects of the lymphoid compartment, and systemic enzyme deficiencies such as hemophilia. One approach for genetic modification of T cells is to introduce therapeutic genes into hematopoietic stem cells that would give rise to cells of the lymphoid lineage. Efficient gene transfer and expression in stem cells is often problematic, however. A more direct approach is to introduce the genes into mature primary T lymphocytes since the transferred genes can be maintained and expressed for long periods by long-lived peripheral T cells. In this report, we describe the adoptive transfer into SCID mice of both murine and human primary T cells that have been efficiently transduced with exogenous genes. Primary murine T cells transduced with a retroviral vector containing the human adenosine deaminase (ADA) gene persisted for at least 5 months in lymphoid organs of SCID mice, continuously expressing the exogenous gene. Primary human T cells were also used as target cells for transfer of the beta-galactosidase (lacZ) gene. Expression of the lacZ gene could be detected in over 20% of the transduced primary T cells before adoptive transfer into SCID mice. Transduced human T cells were injected into SCID mice intraperitoneally (ip), and the beta-galactosidase activity could be detected in cells collected from peritoneal exudate washes of recipient mice 6 weeks post-injection. These results demonstrate the availability of a murine model in which the long-term effects of expression of exogenous genes in both murine and human T cells can be tested.

Adenosine Deaminase↗
PubMed1996

[The profile surgery. Mandibular osteotomies].

During the years 1987-1994, 31 mandibular osteotomies have been performed in 25 patients, 15 had mandibular alteration alone, 10 of them with prognatism, 2 with microretrognatia and 3 with chin hipoplasia. The other 10 had a combined maxillary-mandibular alteration with hipoplasia and maxillary retrussion. The preoperative work-up included cephalometric and dental study, and a cast model was done to asses the theoretical benefic of the osteotomy. All these patients underwent orthodontic treatment before and after surgery. The results have been good or very good in 96% of the cases. The ortognatic surgery offers significant aesthetic and functional improvement to these patients.

Adolescent↗
PubMed1995

Exclusive breast-feeding duration is associated with attitudinal, socioeconomic and biocultural determinants in three Latin American countries.

International health organizations have recommended exclusive breast-feeding (EBF) (i.e., breast milk as the only source of food) as the optimal infant feeding method during the first 4-6 mo of life. Therefore, it is important to document the determinants of EBF in different populations. Low-income urban women from Brazil (n = 446, 2 maternity wards), Honduras (n = 1582, 3 maternity wards) and Mexico (n = 765, 3 maternity wards) were interviewed at birth and in their homes at 1 mo and 2-4 mo after delivery. Multivariate survival analyses (Cox model) indicated that planned duration of EBF (all 3 countries), having a female infant, and not being employed (Brazil and Honduras), lower socioeconomic status (Honduras and Mexico) and higher birth weight (control hospital in Brazil and Honduras) were positively associated (P < or = 0.10) with EBF. Women who delivered in the maternity wards that had more developed breast-feeding promotion programs were more successful with EBF. The association between maternal education and EBF was modified by the maternity ward in Mexico and Honduras. Being > or = 18 y and having a partner living (Brazil) or not (Mexico) living at home were positively associated with EBF. These findings can contribute toward the design of EBF promotion efforts in Latin America.

Adult↗
PubMed1994

Convulsions and inhibition of glutamate decarboxylase by pyridoxal phosphate-gamma-glutamyl hydrazone in the developing rat.

We have previously shown that in the adult rat the inhibition of brain glutamate decarboxylase (GAD) activity by pyridoxal phosphate-gamma-glutamyl hydrazone (PLPGH) administration does not result in convulsions, whereas in the adult mouse intense convulsions invariably occur. In the present study we report that, surprisingly, immature rats from 2 to 20 days of age treated with PLPGH (80 mg/kg) showed generalized tonic-clonic convulsions, whereas no convulsions at all were present in 30 days-old or older rats. GAD activity, measured by enzymic determination of GABA formed in forebrain homogenates, was inhibited by about 60% at the time of convulsions in 15 days-old and younger rats, whereas the inhibition was between 40 and 50% in older animals. The addition of the coenzyme pyridoxal 5'-phosphate to the incubation medium completely reversed this inhibition. In all treated animals GABA levels were lower compared to controls. The results indicate that the susceptibility of GAD in vivo to a diminished cofactor concentration decreases with age. It seems possible that changes in the expression of enzyme forms are reflected in developmental variations in the susceptibility to seizures induced by vitamin B6 depletion, but alterations of other B6-dependent biochemical pathways cannot be discarded.

Animals↗
PubMed1994

Insulin activation of red blood cell Na+/H+ exchange decreases the affinity of sodium sites.

We have previously reported increased activity of Na+/H+ and Na+/Li+ exchanges in red blood cells (RBC) of patients with hypertension and diabetic nephropathy. The presence in human red blood cells (RBC) of insulin receptors has led us to examine the effects of this hormone on the kinetic parameters of Na+/H+ exchange as a first approach to define its mechanism of action. The antiporter activity was measured as net Na+ influx driven by an outward H+ gradient in acid-loaded, Na-depleted RBCs preincubated with or without (w/wo) insulin (0 to 100 microU/ml) for different time periods. The effects of insulin on the H+ and Na+ activation kinetics of Na+/H+ exchange were examined in RBCs of normal subjects fasted for 12 hours. Insulin (50 microU/ml for 1 hr) increased the Vmax from 28 +/- 6 to 49 +/- 8 mmol/liter cell x hr (N = 10, P < 0.0005) and the Km for Na+ from 72 +/- 10 to 142 +/- 19 mM (N = 4, P < 0.05) but did not change the Km for intracellular H+. Insulin also increased the Vmax of Na+/Li+ exchange at pHi 7.4 (0.34 +/- 0.03 to 0.45 +/- 0.04 mmol/liter cell x hr, N = 9, P < 0.005) as well as the Km for Na+ (31 +/- 3 to 6 +/- 10 mM, P < 0.0003). Therefore, insulin can modulate Na+ sites of Na+/Li+ or Na+/H+ exchanges independent of the occupancy of H+ sites to favor the release of bound Na+ into the cytoplasm. Insulin stimulation of Na+/H+ exchange required endogenous cytosolic Ca2+ levels. The kinetic effects of insulin on Na+/H+ and Na+/Li+ exchanges were imitated by okadaic acid (300 microM), an inhibitor of protein phosphatases which dephosphorylate serine-threonine residues. Okadaic acid increased the Vmax of Na+/H+ and Na+/Li+ exchanges and the Km for Na+ as insulin did. In conclusion, insulin stimulation of the Na+/H+ antiporter occurs by a novel kinetic mechanism leading to a decreased affinity for external Na+ without changes in the affinity for Hi. On the basis that insulin effects were imitated by okadaic acid, we hypothesize that this hormone may increase the phosphorylated state of serine-threonine residues of this antiporter protein.

Adult↗
PubMed1994

[Primary antiphospholipid syndrome. Clinical course features of 24 cases].

OBJECTIVES: Describe the clinico-evolutionary characteristics of cases of primary antiphospholipid syndrome (PAPLS) diagnosed at our center. PATIENTS AND METHODS: Retrospective study of all patients with circulating anticoagulant type lupus (AL) (62 patients) and/or anticardiolipin antibodies (ACLA) found in our center since 1981 and 1988, respectively. TTPA, Kaolin's test (KT), and Russel's viper venom time (RVVT) and ACLA type IgG and IgM by ELISA: Only those patients meeting the criteria for PAPLS are included. RESULTS: Twenty-four patients were diagnosed with PAPLS: Eleven patients were from the enlarged TTPA group, 11 of the total with positive ACLA, and two by KT and abnormal RVVT. As for gender, 18 were women. In the past three years, 19 patients were diagnosed. The diagnostic criteria were from the very beginning: venous thrombosis in nine patients, arterial thrombosis in four, aborted repetitions in three, and plateletopenia in eight. Six patients presented pulmonary thromboembolism, the cause of death in one patient. Thrombopenia was manifested in the evolutionary course of 14 patients, only one of which being severe. Two patients have died (one of them from neoplasia), and two others have had antiphospholipid antibodies become negative. Seven patients remain without treatment, the others undergoing anti-aggregating or anti-coagulant treatment. CONCLUSIONS: Plateletopenia, alone or accompanied by other symptoms, is the most common alteration of PAPLS in our area, followed by venous thrombosis which caused death by pulmonary thromboembolism in one patient. Arterial thrombotic events and aborted repetitions are by no means infrequent.

Abortion, Habitual↗
PubMed1993

Effect of intravenous amino acids on protein metabolism of preterm infants during the first three days of life.

Twenty-three preterm infants with respiratory distress syndrome (mean birth weight 1.07 kg, SD 0.24 kg) were randomly assigned to receive glucose alone or glucose with amino acids (1.5 g.kg-1.d-1) i.v. beginning on the 1st d of life. Blood ammonia and serum urea, CO2 content, sodium, potassium, chloride, and ionized calcium concentrations were normal and did not differ between treatment groups. Nitrogen balance was significantly greater in the group that received amino acids [88 (SD 54) versus -135 (SD 45) mg.kg-1.d-1]. In 12 infants (seven, glucose-only; five, glucose and amino acids), leucine kinetic studies were also performed on the 3rd d of life. These 12 infants received a 4-h primed constant infusion of L-[1-13C]leucine. Blood and breath were collected and analyzed for [1-13C]ketoisocaproate and 13CO2, respectively. Leucine turnover and oxidation were calculated. Both leucine turnover and oxidation were significantly higher in the group receiving amino acids than in the glucose-only group [241 (SD 38) versus 164 (SD 25) mumol.kg-1.h-1 and 71 (SD 22) versus 40 (SD 17) mumol.kg-1.h-1, respectively]. In addition, the calculated rate of protein synthesis was higher in the group receiving amino acids [6.9 (SD 1.1) versus 5.0 (SD 1.2) g.kg-1.d-1]. These data indicate that the i.v. administration of amino acids (1.5 g.kg-1.d-1) to ill preterm infants beginning on the 1st d of life improves whole-body protein balance as a result of increased protein synthesis.

Amino Acids↗
PubMed1993

Physiologic levels of uric acid inhibit xanthine oxidase in human plasma.

Xanthine oxidase, a key source of reactive oxygen species, and purine substrates are detected in the circulation after ischemia-reperfusion. High levels of uric acid, produced by a xanthine oxidase-catalyzed reaction, are found in human plasma. We studied whether uric acid could alter xanthine oxidase activity in plasma obtained from eight adults and eight neonates. Known amounts of uric acid were added to xanthine and xanthine oxidase-supplemented buffer and plasma, and the production of uric acid and superoxide was determined. Uric acid, 150 and 300 microM, decreased the oxidation of xanthine to uric acid in adult plasma by 37.5 +/- 5.6 and 48.9 +/- 6.1% and formation of superoxide by 23.2 +/- 1.9 and 32.0 +/- 2.3%, respectively, compared with plasma without uric acid. In newborn plasma, a similar pattern and extent of inhibition was observed. Superoxide formation, however, was inhibited to a greater extent than in adult plasma. Endogenous xanthine oxidase was detected in newborn plasma in nine additional neonates using HPLC. These results indicate that uric acid is an effective inhibitor of the formation of superoxide and hydrogen peroxide by xanthine oxidase at the levels found in human plasma. Plasma uric acid may play an important role in attenuating the oxidant-mediated tissue damage caused by xanthine oxidase released into the circulation during ischemia-reperfusion.

Adult↗
PubMed1993

[Serum levels of immunoglobulins and complement in alcoholic liver disease].

The presence of high serum concentrations of immunoglobulins and hypocomplementemia is commonly observed in alcoholic patients; however, the mechanism behind their production is unknown. We studied 70 subjects (52 alcoholics and 18 healthy controls) prospectively. All the patients were active drinkers who consumed more than 100 gr of ethanol daily for at least 10 years. A biopsy of the liver was performed for all the subjects, along with immunoglobulins, C3, C4, CH100 and tests of liver function. Of the 52 alcoholics in the study, 20 showed minimal changes in hepatic steatosis (group II), 6 isolated severe alcoholic hepatitis (group III), 11 cirrhosis of the liver without alcoholic hepatitis (group IV), and 15 cirrhosis with alcoholic hepatitis (group V). There were no significant differences between the various groups according to age or quantity and duration of intake. The highest concentrations of immunoglobulins was observed in those with cirrhosis of the liver (p < 0.001) regardless of the degree of inflammation. The best correlation was found between IgA and liver histology (r = 0.64; p < 0.001). Hypocomplementemia was a factor only in those patients belonging to histological groups IV and V. Both the immunoglobulins and the complement proteins were narrowly correlated with the tests of liver function, and its alterations were more pronounced in patients with cirrhosis in Child's stage C. We conclude that the hypergammaglobulinemia and hypocomplementemia observed in the alcoholic patients are conditioned fundamentally by the degree of deterioration in liver function, indicated by cirrhosis of the liver upon presentation.

Adult↗
PubMed1993

[Menarche, menstrual and sociodemographic characteristics of Puerto Rican female athletes in the XV and XVI Central American and Caribbean Games].

UNLABELLED: This investigation described maturation, menstrual and socio-demographic characteristics of 65 Puerto Rican women athletes that were interviewed during the XVI Central American and Caribbean Games (CACG), Mexico City in 1990. The results were compared with those of Puerto Rican women athletes (n = 52) at the XV CACG, Santiago Dominican Republic, 1986. The quantitative variables (age, age at initiation of training, years of training, age at menarche, birth order, and family size) were not statistically different (t-independent, p > or = 0.05). The observed frequencies for the qualitative variables (menstrual characteristics, degree of certainty in the recall of age of menarche, use of oral contraceptives, and marital status) were very similar. IN CONCLUSION: the women at the XVI CAC in Mexico demonstrated similar maturational, menstrual and socio-demographic characteristics to the those athletes evaluated four years earlier in Santiago and based on their long history of training, both samples were representative of athletically mature athletes. The findings were very similar to those reported for olympic athletes and such data expands the available information on Puerto Rican women athletes.

Adult↗
PubMed1993

[Cryptococcosis of the central nervous system and infection by HIV. Clinical-evolutive characteristics in 13 cases].

Cryptococcosis is the fourth cause of infection of the Central Nervous System in patients with infection by HIV. Despite this fact, the series published in our country are referred to a limited number of cases. We describe the most relevant characteristics of 13 patients with meningitis by Cryptococcus neoformans. We used as inclusion criteria a positive culture of the Cephalorhachidian Fluid (CRF). We observed a significant reduction in the levels of CD4 lymphocytes in all patients, the absence of meningitic syndrome in more than 50% cases (8/13) and a normal CRF cytobiochemistry in three patients. The thoracic radiography was normal in all cases but two, although the cryptococcus was cultured in a transbronchial biopsia of a patient with normal thoracic radiography. The Computerized Axial Tomography showed frequent alterations (5/13). Eight patients were treated with amphotericin B (0.5 mg/kg/d) and five with fluconazol (400 mg/day). Despite following a maintenance therapy with fluconazol (200 mg/d), we had two cases of recurrence in the group previously treated with fluconazol. The level of leukocytes in the CRF was the only prognosis factor (p < 0.05). Five patients died during their first hospitalization due to causes related to the infection by cryptococcus. New therapeutical guidelines are needed in order to improve the prognosis of these patients.

AIDS-Related Opportunistic Infections↗
PubMed1992

A phase II study of 5-fluorouracil and high-dose folinic acid in combination with cyclophosphamide and mitoxantrone for advanced breast cancer.

38 patients with advanced breast adenocarcinoma were treated in a phase II study with 5-fluorouracil and high-dose folinic acid combined with cyclophosphamide and mitoxantrone. 6 patients had received prior chemotherapy for advanced disease, all with an anthracycline-containing regimen. Treatment was generally well tolerated. The most common side-effect was myelosuppression, with 1 toxic death due to leukopenia-related sepsis. 1 patient developed severe congestive heart failure 12 months from the end of therapy. 36 patients were evaluable for response. The overall response rate was 55%. Median duration of response was 8 months and median survival time was 16 months. This regimen warrants further investigations.

Adult↗