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Biomedical subjects

M Rivas

Publications and source records attributed to M Rivas.

At least 37 records · Page 2Linked to original sources
PubMed1996

Gonadal (ovarian) dysgenesis in 46,XX individuals: frequency of the autosomal recessive form.

Gonadal (ovarian) dysgenesis with normal chromosomes (46,XX) clearly is a heterogeneous condition. In some forms, the defect is restricted to the gonads, whereas other affected females show neurosensory hearing loss (Perrault syndrome). In another form, brothers may have germ cell aplasia [Granat et al., Fertil Steril 1983; 40:215-219]. Nongenetic causes exist as well. To elucidate the proportion of XX gonadal (ovarian) dysgenesis due to autosomal recessive genes, we analyzed published (N = 17) and unpublished (N = 8) families having at least two female offspring. Analysis was restricted to cases in whom ovarian failure was documented by the presence of streak ovaries (published cases) or elevated gonadotropins (unpublished cases). We reasoned that the closer to that segregation ratio expected for an autosomal recessive trait (0.25), the lower the frequency of nongenetic forms. Segregation analysis utilized standard correction for single ascertainment, with only females included in the preliminary analysis. The segregation ratio estimate was 0.16. Our results suggest that many 46,XX females with gonadal (ovarian) dysgenesis represent a disorder segregating as an autosomal recessive trait, placing sisters of these cases at a 25% risk for this disorder.

Female↗
PubMed1996

Fracture after cardiac transplantation: a prospective longitudinal study.

Cardiac transplantation is associated with increased prevalence of vertebral fractures, but the natural history of and risk factors for fracture after this life-saving procedure are unclear. We evaluated 47 patients (34 men and 13 postmenopausal women) before transplantation with spinal radiographs, determination of bone density by dual energy x-ray absorptiometry, and measurement of biochemical indexes of mineral metabolism. During the first year after transplantation, incident fractures were documented radiographically. Associations among demographic characteristics, bone density, biochemistries, and fracture risk were evaluated with logistic regression analysis. Despite supplementation with elemental calcium (1000 mg/day) and vitamin D (400 IU/day), 17 patients (7 women and 10 men) sustained a total of 34 fractures. Most fractures involved the spine, and 85% of the patients who experienced fracture did so within 6 months of transplantation. Fifty-four percent of the women and 29% of the men experienced fracture. Femoral neck bone mineral density was significantly lower in women who experienced fracture than in those who did not (0.604 +/- 0.11 vs. 0.760 +/- 0.12 g/cm2; P < 0.04), but did not differ in men according to fracture outcome. The amount of bone loss at the femoral neck by 6 months after transplantation was significantly greater in men with fracture than in men without fracture (12.0 +/- 6.4% vs. 6.8 +/- 5.3%; P < 0.04), but did not differ in women according to fracture outcome. Pretransplant 1,25-dihydroxyvitamin D levels were significantly lower (25 +/- 9 vs. 39 +/- 17 pg/mL; P < 0.007) and intact PTH levels tended to be higher in men who did not experience fracture (37 +/- 15 vs. 69 +/- 46 pg/mL; P < 0.06). Individual pretransplant bone density measurements demonstrated substantial overlap between patients who did and did not experience fracture, and normal bone density did not necessarily protect against fracture after transplantation. We conclude that fractures are a common and early complication of cardiac transplantation. No pretransplant measurement has yet been identified that reliably predicts fracture after transplantation in the individual patient.

Bone Density↗
PubMed1996

Verocytotoxin-producing Escherichia coli infection in family members of children with hemolytic uremic syndrome.

Thirty-four hemolytic uremic syndrome (HUS) patients and ninety-five family members were studied to determine the frequency of infection with verocytotoxin-producing Escherichia coli (VTEC) in household contacts using three diagnostic criteria: VTEC strains isolation and characterization, detection of free fecal VT (FVT) and VT-neutralizing antibodies (VT-NAbs). Gastrointestinal tract symptoms occurred in one to six family members in 8 (23.5%) of the index cases, the week before admission to hospital or simultaneously. The control group consisted of 34 children with acute gastroenteritis who did not develop HUS. Cumulative evidence of VTEC infection was found in 13 (38.2%) of 34 HUS patients, in 30 (31.6%) of 95 family members and in 10 (29.4%) of 34 control children. The serotypes of VTEC isolated were O157: H7 and O25: H2. The prevalent VT type was VT2 in VTEC and FVT; and VT1 in VT-NAbs. Both parents had the same infection rate by fecal toxin or serological data (11.1% FVT, 32% VT-NAbs). These were higher than those detected in siblings (6.2% FVT, 23.5% VT-NAbs) and grandparents (0% FVT, 18% VT-NAbs). Of 16 patients without evidence of infection, 3 had household contacts with FVT and 13 with VT-NAbs. Our results show the wide dissemination of VTEC in the population of Argentina and that family members of HUS patients are usually infected. Therefore, person-to-person transmission may play an important role in the high incidence of HUS in our country.

Bacterial Toxins↗
PubMed1996

Water permeability properties of the human small intestine in vitro: effects of Escherichia coli heat-stable enterotoxin.

The net absorptive water flux (Jw), the transepithelial potential difference (PD) and the short-circuit current (Isc) were simultaneously measured in the human small intestine in vitro with the following results: 1) An absorptive Jw was observed when the jejunum or the ileum were mounted between two identical standard solutions in the presence of an hydrostatic pressure gradient (delta P) of 13 cm of water (mucosal side positive). 2) The absorptive Jw was a linear function of the applied delta P or the imposed osmotic transepithelial gradient (delta Osm) in both intestinal segments. The hydrostatic (Phydr) and osmotic (Posm) permeabilities to water for jejunum and ileum were: 0.349 +/- 0.049 cm/s vs. 0.156 +/- 0.022 cm/s and 0.0012 +/- 0.0001 cm/s vs. 0.0019 +/- 0.0003, respectively. 3) A fraction of this absorptive Jw was independent of the presence of any hydrostatic, osmotic or chemical gradient and represented the transport associated to movement of water (Jwt). 4) PD and Isc values were similar in the jejunum and in the ileum but the transepithelial resistance (Rt) was significantly greater in ileum than in jejunum. 5) 2 micrograms/ml of E. coli heat-stable enterotoxin (STa) caused a significant inhibition of the absorptive Jw without modification of Phydr, Posm or Isc. 6) After STa treatment, the absorptive Jwt reverted to a secretory one in the jejunum. In the ileum, STa action caused a 48% decrease in the absorptive Jwt values.

Animals↗
PubMed1995

Trisomy 21 and maternal age of menopause: does reproductive age rather than chronological age influence risk of nondisjunction?

The biological basis underlying the increased risk of nondisjunction in offspring of women of advanced maternal age is not understood. We sought to test the hypothesis that maternal reproductive age (distance in time from approaching menopause) rather than chronological age is pivotal in the etiology of nondisjunction. Our results found no difference in age of menopause between women > or = 30 years old at delivery of a child with trisomy 21 (i.e., age-related nondisjunction) compared to controls. Among women < 30 years of age at delivery of a child with trisomy 21, none underwent premature menopause. Therefore, our findings fail to support the theory that reproductive age plays a major role in the etiology of nondisjunction.

Adult↗
PubMed1995

Antibody responses against Escherichia coli heat-labile toxin and colonization factor antigens I and II in Argentinian children.

Serum antibody responses against Escherichia coli heat-labile enterotoxin (LT) and colonization factor antigens (CFAs) I and II were studied in 84 children < 5 years old living in two communities. These villages differed in the quality of their drinking water. Children from both communities developed significantly increased antibody titers against LT and CFA/II but not against CFA/I during 3 months of follow-up. The magnitude of the anti-LT response was significantly higher in children from Zaiman than in those from Las Dolores. Antibody titers rose to maximum levels during the second year of age and reached relatively constant levels in children aged 2-5 years, probably due to repeated exposure to enterotoxigenic E. coli strains. Antibody levels of 30 children were followed for 2 years; increases in anti-LT and anti-CFA titers varied in the different age groups.

Age Factors↗
PubMed1995

Systemic and subcutaneous microvascular oxygen tension in conscious Syrian golden hamsters.

Arteriolar and venular oxygen tension distribution was studied in the subcutaneous connective tissue of the chamber window preparation in conscious Syrian golden hamsters as a function of the systemic PO2, PCO2, pH, arterial pressure and hematocrit, microvascular red blood cell (RBC) velocity, vessel diameter, and blood flow in the same microvessels. PO2 was measured with the phosphorescence decay technique using Pd-meso-tetra(4-carboxyphenyl)porphyrin (30 mg/kg body wt iv). Systemic arterial and venous PO2s were 71.6 +/- 13.1 and 28.4 +/- 5.1 mmHg, while oxygen tension was 45.1 +/- 13.3 mmHg in arterioles and 30.1 +/- 10.7 mmHg in venules. The relatively low arteriolar PO2 and the small arteriolar-venular PO2 gradient indicate that some blood oxygen exits directly to the tissue or is shunted before reaching the capillaries. RBC velocity was the strongest correlate of microvascular PO2 (arterial correlation coefficient = 0.503 and venous correlation coefficient = 0.560, P < 0.001). Microvascular PO2 was also correlated with blood flow, vessel diameter, blood pH, and PCO2 but not with systemic PO2. Arterial oxygen tension was only significantly related to PCO2, pH, and hematocrit. These findings suggest that oxygen delivery to the tissue improves with increasing blood flow velocity and that microvascular PO2 is a locally regulated parameter in the absence of major systemic perturbations.

Animals↗
PubMed1995

[Enterohemorrhagic Escherichia coli in hemolytic uremic syndrome in Chilean children. Evaluation of different technics in the diagnosis of the infection].

Enterohemorrhagic Escherichia coli (EHEC), have been associated with pathogenesis of hemolytic uremic syndrome (HUS) worldwide. Our aim was to determine the association of EHEC infection and HUS in Chilean children. During may 1991 and october 1993, 34 children with HUS and 33 age matched controls (children with diarrhea that did not develop HUS) were enrolled in a case/control study. For each child a stool and serum sample were obtained at admission. Stools were processed for common enteropathogens and for EHEC identification. EHEC were identified in stools by gene probes for different virulence factors (EHEC plasmid-associated fimbria, Shiga-like toxin I, Shiga-like toxin II and eae adherence factor) and by detection of free fecal toxin by a neutralization assay in Vero cells. Sera were processed for anti-cytotoxin antibodies also by an assay in Vero cells. Enteropathogens were isolated in 20.6% and 15.5% of HUS and control children respectively (p = NS). 91% of the HUS children and 73% of the control children were EHEC positive by one or more of the techniques used (p = 0.05). Of the three detection methods used for EHEC, only free fecal cytotoxin was significantly more common in HUS children than controls (45.5% vs 9% p = 0.007). Genotype patterns of HUS and controls strains were similar except for a trend towards a higher frequency of non-toxigenic strains in the control group. Serogroup O157 was more common in HUS children than in controls (9% vs 0% p = 0.036). In Chile as in other countries, EHEC infection is common and significantly associated with occurrence of HUS. Infection with EHEC strain O157 seems to be an important risk factor for HUS.

Bacterial Typing Techniques↗
PubMed1994

Direct detection of Vibrio cholerae in stool samples.

A direct method to detect Vibrio cholerae in stool samples was developed by using a PCR procedure that did not require a DNA purification step. Dilution (1/100) of stool samples prevented inhibition of the reaction by contaminants, and two consecutive PCRs, the second one with a nested primer, achieved the desired sensitivity. Comparison of the results obtained from stool swab samples processed by the two-step PCR and by an enzyme-linked immunosorbent assay using GM1 as the capture molecule showed that the former is more sensitive and gave positive results even when V. cholerae was not culturable or dead.

Argentina↗
PubMed1993

Identification of toxigenic Vibrio cholerae from the Argentine outbreak by PCR for ctx A1 and ctx A2-B.

A polymerase chain reaction (PCR) to detect a region of the A1 cholera toxin gene was applied to the identification of 43 Vibrio cholerae strains isolated from the recent outbreak in Argentina. A good correlation was observed between the GM1-enzyme-linked immunosorbent assay (GM1-ELISA) to detect the B subunit of the enterotoxin and PCR. However, a V. cholerae non-01 strain that was negative by the ELISA test, was positive by the PCR assay for the A1 region. A second PCR test to detect the A2-B coding region was developed to solve this case. We propose that routine detection of toxigenic V. cholerae by PCR should include analysis of A2-B coding region or the whole cholera toxin operon.

Argentina↗
PubMed1993

Hemolytic uremic syndrome: co-infection with two different serotypes of Shiga-like toxin producing Escherichia coli.

We report a case of a child who developed Hemolytic Uremic Syndrome in whom two Shiga-like toxin (SLT)-producing Escherichia coli strains of different serotypes and genotypes, were simultaneously isolated from stools. In addition, one of these strains represented a new toxin producing serotype. Strain 1 belonged to serotype O157: H7, biotype D, produced SLT II and was susceptible to all antibiotics tested. This strain hybridized with gene probes for SLT II, fimbrial adhesion (EHEC factor) and attaching and effacing factor (eae). Strain 2 belonged to serotype 025: K2: H2, produced SLT II and had a multiresistant antibiotic susceptibility pattern. This strain hybridized with the EHEC gene probe but not with SLT I, SLT II and eae gene probes. Free fecal SLT II cytotoxin was detected in stools of the child and his father, suggesting that the infection may have been acquired from a household contact.

Bacterial Toxins↗
PubMed1993

[Diagnosis of entero-invasive Escherichia coli associated with diarrhea].

Sixteen Escherichia coli strains isolated from diarrhea patients, characterized as enteroinvasive (EIEC) by the keratoconjunctivitis test (Sereny test), and 15 non-EIEC strains, were studied. The aim of this study was to establish a possible correlation between the Sereny test and several other tests as enzyme-linked immunosorbent assay (ELISA) and biochemical markers, which are more easily accessible to general practice laboratories. Strains were assayed for the virulence marker antigen (the outer membrane proteins) by direct ELISA, biochemical tests, antimicrobial susceptibility profile and serotyping. Mean optical density (OD) values in the ELISA were 2.018 +/- 0.336 for EIEC strains, and 0.569 +/- 0.283 for non-EIEC strains. Difference between the OD values of the two groups was found to be significant at p < 0.01 by the one-tailed Student's test. One (6.2%) of the 16 Sereny test-positive strains was negative by ELISA. Considered as a group, the EIEC strains are rather heterogeneous in their biochemical characteristics. Lysine decarboxylase test appeared as the most relevant assay, since all EIEC strains were negative for this enzyme, whereas 66.7% of non-EIEC strains were positive. Other helpful tests performed for strain characterization were: gas production from glucose and from glycerol, sucrose and salicin fermentation, and esculin hydrolysis (p < 0.01). However, strains behaviour was variable with these tests. Differences between both groups of strains with regard to mucate utilization and dulcitol fermentation was significative only to a 5% level. Antibiotic sensitivity patterns showed differences between EIEC and non-EIEC strains: 37.5% of the former vs 80% of the latter, were resistant to at least four of the antibiotics tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Studies of the effect of cyclosporine in psoriasis in vivo: combined effects on activated T lymphocytes and epidermal regenerative maturation.

Cyclosporine (CSA) decreases lymphokine synthesis and keratinocyte proliferation in vitro, but its in vivo mechanism of action in treating recalcitrant psoriasis is incompletely understood. Ten psoriasis patients were treated with CSA (2-7.5 mg/kg/d) with clinical improvement in nine of 10 patients. Skin biopsies before and after 1-3 months of CSA treatment were studied for evidence of immune and keratinocyte activation using immunoperoxidase and Northern blotting analysis. The number of activated, IL-2 receptor+ T cells in plaques after CSA treatment was reduced in all patients by a mean of 60%. Seven of 10 patients showed a decrease in keratinocyte HLA-DR expression; five of seven showed a decrease in gamma-IP-10 immunoreactivity, suggesting a decline in gamma interferon levels in plaques after CSA therapy. We studied the effect of CSA treatment in vivo on TGF-alpha, IL-6, and keratin K16 expression, three markers of keratinocyte growth activation. Expression of keratinocyte TGF-alpha and IL-6, which are elevated in active psoriatic epidermis, did not change in these patients after CSA treatment. The majority of patients (five of eight) continued to express the hyperproliferative keratin K16 after CSA treatment. Our results suggest that the predominant direct mechanism of action of Cyclosporine in vivo is a diminution of T-cell activation in plaques, with attendant decreased lymphokine production.

Cyclosporine↗
PubMed1992

Relationship between enterotoxigenic Escherichia coli and diarrhea among children in Buenos Aires.

The incidence of enterotoxigenic Escherichia coli (ETEC) has been studied in 85 children with acute diarrhea in patients in the Hospital de Niños Pedro de Elizalde, Buenos Aires, and in 38 healthy children. All of them were up to four years old and none had received antibiotic treatment within 7 days before sampling. ETEC was recovered in 9 out of 85 (10.6%) children with diarrhea. From these positive cases, 6 were associated with heat-stable (ST), 1 with heat-labile (LT) and 2 with both LT and ST enterotoxins. Only one case (2.6%) of LT-producing ETEC was detected in the control group. In 5 out of 9 ETEC diarrhea cases (55.5%) the isolated strains expressed human colonization factor antigens (CFA); four of them were CFA/I and one CFA/II. The characteristics of the CFA, biotype, serotype and antibiotic sensitivity pattern were studied in 23 E. coli isolates from 10 ETEC positive children. Of the 12 ST only strains, 5 (41.7%) expressed CFA/I and 2 (16.7%) CFA/II (CS2 + CS3). One out of 2 LT/ST strains expressed CFA/I. CFAs were not detected in the ETEC-LT nor in the toxin negative E. coli strains. From the ETEC isolated, 82.4% were resistant to 4 or more antibiotics, whereas only 50% of simultaneously isolated toxin-negative E. coli presented this sensitivity pattern. The different ETEC strains belonged to several different serotypes, some of them rarely observed in other countries. None of these serotypes correlated either with the toxin profile or with the sugar fermentation pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Argentina↗
PubMed1991

Colonization factors of enterotoxigenic Escherichia coli isolated from children with diarrhea in Argentina.

A prospective study was performed to evaluate the presence of colonization factor antigens (CFAs) in enterotoxigenic Escherichia coli (ETEC) strains isolated from 1,211 children with diarrhea in Argentina. One hundred nine ETEC strains that were isolated from seven different laboratories in various regions of the country were tested for CFAs by using monoclonal antibodies against CFA/I and E. coli surface antigens CS1, CS2, and CS3 of CFA/II and CS4 and CS5 of CFA/IV; a polyclonal antiserum against CS6 was used. The CFAs searched for were found in 52% of the ETEC strains: 23% of the strains carried CFA/I, 17% carried CFA/IV, and 12% carried CFA/II. All of the CFA/I strains produced heat-stable enterotoxin, and several of them were of the prevalent serotypes O153:H45 and O78:H12. Among the 19 strains expressing CFA/IV, 16 expressed CS5 and CS6 and produced the heat-stable enterotoxin and most were of serotype O128:H21; the remaining 3 strains produced CS6 only. No ETEC strains expressing CS4 were found. Most (11 of 13) of the CFA/II-carrying ETEC strains expressed CS1 and CS3, and 10 of them were of the O6:K15:H16 serotype and produced both heat-labile and heat-stable toxins. As many as 24 of the 109 CFA-negative ETEC strains gave mannose-resistant hemagglutination with erythrocytes from different species; 4 strains had high surface hydrophobicity, suggesting the presence of additional, as yet undefined, colonization factors in up to 25% of the ETEC isolates.

Antigens, Bacterial↗