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Biomedical subjects

R Rivera

Publications and source records attributed to R Rivera.

At least 37 records · Page 2Linked to original sources
PubMed1999

Analysis of client characteristics that may affect early discontinuation of the TCu-380A IUD.

The purpose of this study was to analyze the reasons for early discontinuation of the TCu-380A IUD in women participating in a large multicenter trial. The study relates specific characteristics of the women at the time of TCu-380A insertion with specific 1-year reasons for discontinuation. A secondary analysis was performed on data obtained from 2748 women from sites in Africa, Asia, and Latin America. By the end of the year, 321 discontinuations were observed. The gross cumulative 12-month life table rates of reasons for discontinuation were 13.3 for all reasons and 3.1, 4.5, and 4.3 for expulsion, removals for bleeding/pain, and personal reasons, respectively. Study site, age, and religion had a significant effect on early discontinuation. Women who had IUD insertions in the African centers had significantly higher expulsion rates than women from other centers. Women < 20 years old had significantly higher expulsion rates than older women. Muslim women had significantly higher rates of removal for bleeding and pain than women of other religions. This information may guide the counseling and follow-up process of women with such characteristics and result in a more satisfactory use and improved continuation rates of the TCu 380A.

Adolescent↗
PubMed1999

Bcl-2, Bax and Bcl-x expression following kainic acid administration at convulsant doses in the rat.

Neuronal death was produced in the CA1 and CA3 areas of the hippocampus, amygdala, and piriform and entorhinal cortices after intraperitioneal administration of kainic acid at convulsant doses to adult rats. To assess the involvement of members of the Bcl-2 family in cell death or survival, immunohistochemistry, western and northern blotting to Bcl-2, Bcl-x and Bax, and in situ hybridization to Bax were examined at different time-points after kainic acid treatment. Members of the Bcl-2 family were expressed in the cytoplasm of pyramidal neurons in the hippocampus, and in a subset of neurons of the piriform and the entorhinal cortices, amygdala and neocortex in the normal adult brain. Dying neurons in the pyramidal cell layer of CA1 and CA3 areas, entorhinal and piriform cortices, and amygdala also expressed Bcl-2, Bax and Bcl-x following excitotoxicity, although many dying cells did not. In addition, a number of cells in the affected areas showed Bax immunoreactivity in their nuclei at 24-48 h following kainic acid administration, thus indicating Bax nuclear translocation in a subset of dying cells. Western blots disclosed no modifications in the intensity of the bands corresponding to Bcl-2, Bcl-x and Bax, between control and kainic acid-treated rats. No modifications in the intensity of the bcl-2 messenger RNA band on northern blots was observed in kainic acid-treated rats. However, a progressive increase in the intensity of the bax messenger RNA band was found in kainic acid-treated rats at 6 h, 12 h and 24 h following kainic acid administration. Interestingly, a slight increase in Bax immunoreactivity was observed in the cytoplasm of neurons of the dentate gyrus at 24-48 h, a feature which matches the increase of bax messenger RNA in the same area, as shown by in situ hybridization at 12-24 h following kainic acid injection. The present results suggest that cell death or survival does not correlate with modifications of Bcl-2, Bax and Bcl-x protein, and messenger RNA expression, but rather that kainic acid excitotoxicity is associated with Bax translocation to the nucleus in a subset of dying cells.

Animals↗
PubMed1999

Decreased disk-eminence ratio is associated with advanced stages of temporomandibular joint internal derangement.

OBJECTIVE: To examine the possible correlation between the stage of internal derangement and the antero-posterior length of the disk in relation to the length of the articular eminence. STUDY DESIGN: Twenty asymptomatic volunteers with normal joints and 120 patients with TMJ dysfunction underwent MR imaging. The A-P length of the disk in relation to the length of the articular eminence (D/E ratio) was measured. RESULTS: The D/E ratio was 0.95 in the asymptomatic volunteers, 0.83 in patients with disk displacement with reduction, 0.74 in those with disk displacement without reduction and 0.57 in the patients with disk displacement and osteoarthritis. The relationship between the D/E ratio and the stage of internal derangement was statistically significant (P<0.01). CONCLUSION: The D/E ratio decreases with advancing internal derangement. We suggest that it is a reliable numerical method for staging the degree of the internal derangement.

Adult↗
PubMed1999

Isolation and characterization of polymorphic microsatellites in Cocos nucifera L.

Microsatellites or simple sequence repeats (SSRs) were isolated from coconut (Cocos nucifera) and tested for polymorphism on restricted germplasm. Sequencing of 197 clones from a cv. Tagnanan Tall-enriched genomic library showed that 75% contained a microsatellite, of which 64% were dinucleotide (GA/CT, CA/GT and GC/CG), 6% were trinucleotide, and 30% were compound repeats. Of 41 primer pairs tested on Tagnanan Tall genomic DNA, 38 gave the expected size product, two amplified two loci, and another gave a multilocus pattern. On 20 coconut samples, the 38 SSRs detected 198 alleles (average: 5.2 alleles per microsatellite). Genetic diversity (D = 1 - sigma pi2) values ranged from 0.141 to 0.809. Heterozygotes were present at high frequencies among some dwarf samples. Analysis of similarity matrices based either on shared alleles at each locus (simple matching coefficient) or on allele bands across all loci (Jaccard coefficient) showed similar results. Dwarfs grouped separately from talls and showed less genetic diversity. In a wider test on 40 samples, 8 SSRs detected 64 alleles (average: eight alleles per microsatellite). These results indicate the high potential of microsatellites to detect genetic diversity in coconut germplasm.

Cocos↗
PubMed1999

Evidence for an interaction between adducin and Na(+)-K(+)-ATPase: relation to genetic hypertension.

Adducin point mutations are associated with genetic hypertension in Milan hypertensive strain (MHS) rats and in humans. In transfected cells, adducin affects actin cytoskeleton organization and increases the Na(+)-K(+)-pump rate. The present study has investigated whether rat and human adducin polymorphisms differently modulate rat renal Na(+)-K(+)-ATPase in vitro. We report the following. 1) Both rat and human adducins stimulate Na(+)-K(+)-ATPase activity, with apparent affinity in tens of nanomolar concentrations. 2) MHS and Milan normotensive strain (MNS) adducins raise the apparent ATP affinity for Na(+)-K(+)-ATPase. 3) The mechanism of action of adducin appears to involve a selective acceleration of the rate of the conformational change E(2) (K) --> E(1) (Na) or E(2)(K). ATP --> E(1)Na. ATP. 4) Apparent affinities for mutant rat and human adducins are significantly higher than those for wild types. 5) Recombinant human alpha- and beta-adducins stimulate Na(+)-K(+)-ATPase activity, as do the COOH-terminal tails, and the mutant proteins display higher affinities than the wild types. 6) The cytoskeletal protein ankyrin, which is known to bind to Na(+)-K(+)-ATPase, also stimulates enzyme activity, whereas BSA is without effect; the effects of adducin and ankyrin when acting together are not additive. 7) Pig kidney medulla microsomes appear to contain endogenous adducin; in contrast with purified pig kidney Na(+)-K(+)-ATPase, which does not contain adducin, added adducin stimulates the Na(+)-K(+)-ATPase activity of microsomes only about one-half as much as that of purified Na(+)-K(+)-ATPase. Our findings strongly imply the existence of a direct and specific interaction between adducin and Na(+)-K(+)-ATPase in vitro and also suggest the possibility of such an interaction in intact renal membranes.

Animals↗
PubMed1999

Left ventricular mass, stroke volume, and ouabain-like factor in essential hypertension.

Many patients with essential hypertension (EH) exhibit increased left ventricular mass. Similarly, elevated circulating levels of an endogenous ouabainlike factor (OLF) have been described in some but not all patients with EH. Moreover, ouabain has a hypertrophic influence on isolated cardiac myocytes. Accordingly, we investigated relationships among plasma OLF, left ventricular mass, and cardiac function in patients with EH. Plasma OLF was determined in 110 normotensive subjects and 128 patients with EH. Echocardiographic parameters and humoral determinants were measured in EH. Plasma OLF levels were increased (P<0.0001) in patients with EH (377+/-19 pmol/L) versus normotensive (253+/-53 pmol/L) subjects. The distribution of plasma OLF was unimodal in normotensives, whereas it was bimodal in EH. Twenty-four-hour diastolic ambulatory blood pressure was slighter higher in EH with high OLF compared with EH with normal OLF (93.2+/-1.14 versus 89.4+/-1.33 mm Hg, P=0.03). Left ventricular mass index and stroke volume in EH with high OLF were greater than in EH with normal OLF (101.9+/-3.3 versus 86.1+/-2.5 g/m(2), P=0.0003, and 57.10+/-1.48 versus 52.30+/-1.14 mL/m(2), P=0. 02, respectively), although heart rate was slower (74.2+/-1.3 versus 80.5+/-1.3 bpm, P=0.005). Multiple regression analysis that tested the influence of body mass index, age, gender, 24-hour blood pressure, and OLF on left ventricular mass revealed independent contributions of systolic (13.2%) and diastolic (12.4%) blood pressure and plasma OLF (11.6%) to left ventricular mass. We conclude that approximately 50% of patients with uncomplicated EH have elevated-high circulating OLF levels, higher diastolic blood pressure, greater left ventricular mass and stroke volume, and reduced heart rate. We propose that the OLF affects cardiovascular function and structure and should be considered as a factor that contributes to the risk of morbid events.

Adult↗
PubMed1998

Oral immunization with enterocoated microbeads induces antigen-specific cytolytic T-cell responses.

A cytolytic T-lymphocyte (CTL) response has been generated to a protein antigen via oral administration in an experimental murine system. This was achieved by the formulation of the test antigen ovalbumin (OVA) in a pH-sensitive microsphere particle (microbead) with an acrylic-based coating to avoid its degradation by gastric enzymes. Comparative studies of orally administered enterocoated microbead-OVA particles, versus the more traditional formulation of OVA in adjuvant (DETOX-PC) given subcutaneously as immunogen, were conducted; both elicited comparable responses in the generation of antigen-specific lymphoproliferative and CTL responses. CTL lines generated via oral administration of antigen were shown to be CD3(+), CD4(-), and CD8(+). CTL lysis of OVA peptide-pulsed targets was shown to be inhibited by anti-CD8 antibody. Whereas oral administration of pH-sensitive enterocoated microbeads containing proteins has previously been shown to elicit antibody and lymphoproliferative T-cell responses to protein antigens, this is the first demonstration of the generation of an antigen-specific cytolytic T-cell response via oral administration of a protein immunogen formulated in such microbeads.

Administration, Oral↗
PubMed1998

Bcl-2, Bax, and Bcl-x expression in the CA1 area of the hippocampus following transient forebrain ischemia in the adult gerbil.

Delayed neuronal death was produced in the CA1 area of the hippocampus following 5 min of forebrain ischemia in adult gerbils. Immunohistochemistry and Western blotting to Bcl-2, Bax, and Bcl-x was examined in control (age-matched, non-operated and sham-operated) and ischemic gerbils. Bcl-2 immunoreactivity was low in CA1 neurons, but Bax was highly expressed in CA1 neurons of control gerbils. Moderate Bcl-x immunoreactivity was observed in control CA1 neurons. Strong Bcl-2 and Bcl-x immunoreactivity was found in CA1 neurons following ischemia. Bcl-2, Bax, and Bcl-x were localized in dying cells, thus suggesting that expression of Bcl-2 was not sufficient to prevent nerve cells from dying. Although the Bcl-x antibody does not discriminate between Bcl-xL and Bcl-xS content in tissue sections, Western blots disclosed a marked increase in the intensity of the band corresponding to Bcl-xS, but not of the band corresponding to Bcl-xL in ischemic hippocampi, thus indicating that the increase in Bcl-xS is associated with delayed cell death following transient forebrain ischemia in the adult gerbil.

Animals↗
PubMed1998

Non-physician insertion of IUDs: clinical outcomes among TCu380A insertions in three developing-country clinics.

Insertion of IUDs by trained non-physicians is increasing. This secondary analysis of TCu380A IUD acceptors collected at clinics in Nigeria, Turkey and Mexico involved 367 women; 193 insertions were performed by physicians and 174 by non-physicians. Women having their IUD inserted by a non-physician were more likely to experience a pain-free insertion, but also likelier to have the IUD removed for bleeding and pain or to experience an expulsion than women who had their IUD inserted by a physician. Early discontinuation rates were similar between the two groups. Overall continuation rates were statistically higher for IUDs inserted by physicians only at the Mexico site. Trained non-physicians can probably safely insert the TCu380A IUD. Appropriate competency-based training is required to limit the number of expulsions and removals for bleeding and pain by non-physicians.

Adult↗
PubMed1998

Alpha-adducin polymorphisms and renal sodium handling in essential hypertensive patients.

The relationship between blood pressure and sodium (Na) excretion is less steep in hypertension caused by increased renal tubular reabsorption. We recently demonstrated that one mutation in rat alpha-adducin gene: (1) is responsible for approximately 50% of the hypertension of MHS rats, and (2) stimulates tubular Na-K pump activity when transfected in renal epithelial cell, suggesting that its pressor effect may occur because an increased tubular reabsorption. Linkage and association studies demonstrated that the alpha-adducin locus is relevant for human hypertension. A point mutation (G460W) was found in human alpha-adducin gene, the 460W variant (G/W) is more frequent in hypertensives than in normotensives. The aim of this study was to test whether acute changes in body Na may differently affect blood pressure in humans as a function of alpha-adducin genotype. The pressure-natriuresis relationship was analyzed in 108 hypertensive using two different acute maneuvers: Na removal (furosemide 25 mg p.o.) and, two days later, Na load (310 mmoles i.v. in 2 hr). We found that 80 patients were wild-type homozygous (G/G), 26 were G/W heterozygous, and 2 were W/W homozygous with similar blood pressure, age body mass index, gender, plasma and urinary sodium and potassium. In basal condition G/W-W/W patients showed a lower plasma renin activity and fractional excretion of Na. In either case the pressure-natriuresis relationship was less sleep in G/W-W/W than in G/G patients, obviously negative for Na depletion with furosemide (-0.011 +/- 0.004 vs. -0.002 +/- 0.002 mm Hg/mumol/min, P < 0.03), and positive for Na load (0.086 +/- 0.02 vs. 0.027 +/- 0.007 mm Hg/mumol/min, P < 0.001). The finding of reduced slope after Na depletion or Na load supports the hypothesis that, as MHS rats, humans bearing one W alpha-adducin variant display an increased of renal tubular sodium reabsorption.

Adult↗
PubMed1998

Development of an animal model to assess the immunogenicity of single-dose tetanus and diphtheria vaccines based on controlled release from biodegradable polymer microspheres.

We have determined threshold doses of aluminium phosphate (AlPO4) adsorbed tetanus toxoid (TT) and diphtheria toxoid (DT) in mice and guinea pigs with a view to developing an animal model to assess the immunogenicity of controlled release vaccines. A dose was sought (threshold dose) which produces little antibody after primary injection and a moderate response after a booster injection, thus mimicking the adult human response to TT and DT vaccines adsorbed on to aluminium adjuvants. After the first injection, mice and guinea pigs showed a dose response for both tetanus toxin IgG antibodies and tetanus antitoxin over a wide range of doses of AlPO4-adsorbed TT (0.01 to 0.2 Lf). After the second and third injections, there was no clear dose response for doses between 0.05 and 0.2 Lf However, doses between 0.01 and 0.04 Lf still showed a dose response after the second injection. Dilution of AlPO4-adsorbed TT in saline just before injection did not alter immunogenicity after the first injection, but stronger booster responses were seen in mice to diluted versus undiluted vaccine after the second and third injections. The threshold dose of AlPO4-adsorbed TT for both mice and guinea pigs was 0.01 Lf given in 100 microliters. For AlPO4-adsorbed DT, three strains of mice (inbred, Balb/c and C57/B6, and outbred, CD-1) showed a dose response after the first injection for DT IgG antibodies and diphtheria antitoxin at 0.1 and 0.2 Lf doses. Outbred CD-1 mice showed a dose response after the second and third injections also, whereas inbred mice showed inconsistent dose responses after the second injection and none after the third injection. In contrast to AlPO4-adsorbed TT, mice injected with undiluted AlPO4-adsorbed DT elicited significantly higher antibodies than those injected with diluted formulations, particularly after the first injection. The threshold dose of AlPO4-adsorbed DT for mice was 0.1 Lf in a volume of 250 microliters. Lower doses did not produce consistent antibody responses in mice. We propose that a single dose of controlled release formulations at doses not greater than 1/10 of a single human dose when injected into mice and guinea pigs should produce an antibody response similar or higher than two to three threshold doses of AlPO4-adsorbed TT or DT.

Adjuvants, Immunologic↗
PubMed1997

Characterization of voltage-dependent calcium influx in human erythrocytes by fura-2.

Thus far, the methods used to determine erythrocyte Ca2+ influx have not allowed the assessment of the kinetics of ion uptake. To overcome this drawback, we studied a new method, using the fluorescent Ca2+-chelator fura-2, which directly quantifies intracellular Ca2+ changes in human erythrocytes. This method has the advantage over previous techniques that it monitors continuously cellular Ca2+ levels. The Ca2+ influx is modulated by cellular membrane potential in the presence of a transmembrane Ca2+ concentration gradient and exhibits a first slow increase of the intracellular Ca2+ concentration, followed, after the reachment of a threshold value of 125 +/- 13 nM Ca2+, by a faster increase until a plateau is reached. The influx rate is inhibited by dihydropyridines in the micromolar range. These findings support the hypothesis that erythrocyte Ca2+ influx is mediated by a carrier similar to the slow Ca2+ channels and is dependent on membrane depolarization.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1997

Polymorphisms of alpha-adducin and salt sensitivity in patients with essential hypertension.

BACKGROUND: Abnormalities in renal sodium transport may be involved in hypertension. Adducin, an alpha/beta heterodimeric protein found in the renal tubule is thought to regulate ion transport through changes in the actin cytoskeleton. We investigated whether an alpha-adducin polymorphism (Gly 460 Trp) is involved in essential hypertension in two separate populations. METHODS: Linkage analysis of three DNA markers at different distances from the alpha-adducin locus (20-2500 kb) was done in 137 hypertensive sibling-pairs. 477 hypertensive and 322 normotensive individuals were genotyped for the alpha-adducin polymorphism. The blood-pressure response to acute and chronic changes in sodium balance was studied in hypertensive individuals with and without the 460 Trp alpha-adducin allele. FINDINGS: Significant linkage was found for all three markers in the sibling-pair study. The extra shared alleles (9.1%, 6.5%, and 4.7%) and the significance level for linkage (p = 0.0006, p = 0.0119, and p = 0.0211) both decreased with increasing distance from the alpha-adducin locus. There was a significant association between the 460 Trp mutation and hypertension (p = 0.0003). In the salt-sensitivity test, to assess the acute blood-pressure response to changes in body sodium in 86 hypertensive patients, the decrease in mean arterial pressure was greater in 65 patients who were heterozygous for the mutant allele (Gly/Trp) than in 21 wild-type homozygotes (Gly/Gly) (mean decrease 15.9 [SE 2.0] vs 7.4 [1.3] mm Hg; p = 0.001). Similarly, 21 heterozygous hypertensive patients showed a greater fall in mean arterial pressure in response to 2 months' treatment with hydrochlorothiazide than did 37 wild-type homozygous hypertensive patients (mean decrease 14.7 [2.2] vs 6.8 [1.4] mm Hg; p = 0.002). INTERPRETATION: Our findings of significant linkage of the alpha-adducin locus to essential hypertension and greater sensitivity to changes in sodium balance among patients with the mutant allele suggest that alpha-adducin is associated with a salt-sensitive form of essential hypertension. We suggest the alpha-adducin polymorphism may identify hypertensive patients who will benefit from diuretic treatment or manoeuvres to reduce total body sodium.

Aged↗
PubMed1997

Efficacy of fine-needle aspiration biopsy of thyroid nodules: experience of a Mexican institution.

In most centers only selected patients with high risk thyroid nodules undergo thyroid surgery, and fine needle aspiration biopsy (FNA) is used to select patients for surgical treatment. The aim of the present study was to evaluate the impact of FNA on the management of thyroid nodules at our institution. A total of 872 patients who underwent FNA over a period of 7 years were retrospectively analyzed. There were 66 men and 806 women with a mean age of 40 +/- 15 years. Altogether 549 patients presented with a thyroid nodule and 323 with multinodular disease. The sensitivity and specificity of FNA were 90.0% and 99.8%, respectively. The positive and negative predictive values were 98% and 99%, respectively, and the accuracy was 99%. Our results are in agreement with those of other reports establishing that FNA of the thyroid is safe, reliable, and effective for differentiating benign from malignant nodules.

Adolescent↗
PubMed1997

Role burdens: the impact of employment and family responsibilities on the health status of Latino women.

This paper explores the relative effects of employment and family responsibility on the perceived health status of Latino women. The data source analyzed for this study was the 1990 Panel Study of Income Dynamics/Latino National Political Survey (PSID/LNPS) Early-Release File (n = 1,502). Regression analyses were used to investigate the contributions of variables associated with perceived health status, including sociodemographics, Latino ethnicity, language, employment, and family responsibility. The results suggest that annual employment hours, occupation, and family responsibilities, such as child care and weekly housework, significantly affect self-reported health status of employed Latinas. Both social causation and social selection may be underlying the associations found. The results suggest that there is need for the development of public policies that seek to increase Latinas' labor force participation rate since any expansion has the potential to have a positive impact on their health status.

Adolescent↗
PubMed1997

Vaginectomy: Profile of Success in Treating Vaginal Prolapse.

Treatment of procidentia and vaginal inversion in older women either with pessaries or surgery commonly brings poor results. Women are unable to retain the pessary; they develop vaginitis and vaginal ulcerations; and surgical "correction" fails due to age-induced genital atrophy or previous obstetrical trauma. We performed a retrospective chart review to assess results of our own technique of vaginectomy/hysterectomy and pelvic floor closure for vaginal vault prolapse and procidentia in 26 aged sexually inactive women seen in our practice. The women ranged from 63 to 83 years of age and had borne 0 to 9 children. Where possible, an estrogen-containing medication was introduced into the vagina preoperatively to stimulate thickening of the vaginal mucosa. A standard Heaney or Doderlein vaginal hysterectomy was performed. Operative time averaged 100 minutes, blood loss averaged 278mL, and 5 patients required a blood transfusion. All patients were discharged in good condition after an average stay of 4.67 days, although 9 of the 24 patients had complications. Since body-cavity invasion was minimal, postoperative care was simple, consisting of hydration with intravenous fluids, urine drainage utilizing an indwelling catheter, (while preventing bladder distension), early ambulation, and prophylaxis against infection and thromboembolism.

Journal Article↗
PubMed1996

CREB-1 and CREB-2 immunoreactivity in the rat brain.

This study is focused to learn about the cellular localization of transcription factors binding to the cAMP response element-CREBs-in the brain of normal rats and in animals subjected to excitotoxic cell damage. For this purpose, CREB-1 and CREB-2 immunoreactivity is examined in the developing and adult rat brain under physiological conditions, and following systemic kainic acid (KA) injection at convulsant doses in the adult, as a validated experimental model of excitotoxic injury. CREB-1 immunoreactivity is constitutively expressed in periventricular glia and Bergmann glia, and appears in reactive astrocytes following KA-induced excitotoxic cell damage. In contrast, CREB-2 is constitutively expressed in all neurons of the cerebrum, cerebellum and brain stem in the developing and adult brain. CREB-2 immunoreactivity is not increased following KA excitotoxic cell damage. These results demonstrate that CREB-1 and CREB-2 in the brain of the rat are localized in separate cellular compartments and that their expression is differentially regulated in pathologic states.

Animals↗