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Biomedical subjects

C Cervantes

Publications and source records attributed to C Cervantes.

72 records · Page 4Linked to original sources
PubMed1975

Familial true hermaphrodism in three siblings: clinical, cytogenetic, histological and hormonal studies.

Three affected siblings with the hermaphrodism are described. The propositi showed the following characteristics: male phenotype and gender role, hypospadias, bilateral scrotal ovotestes with palpable nodules, and absence of müllerian structures. The X chromatin was positive and the Y chromatin was negative in the 3 affected subjects. Their karyotype in peripheral blood lymphocytes and in gonadal fibroblasts was 46,XX and no Y chromosome fluorescence was observed. Plasma FSH was elevated in the 2 older patients and plasma LH was elevated only in the oldest. Plasma testosterone was low and plasma estradiol high in the 3 siblings; plasma progesterone was elevated in 2, but normal in 1 sibling. Since some of the clinical characteristics of these 3 affected siblings are not the most common features in the majority of sporadic cases of true hermaphrodism, it is suggested that the presence of all of them may be the first clue for the clinical suspicion of the familial type of true hermaphrodism.

Adolescent↗
PubMed1975

Effect of paramethasone acetate on ovarian steroids and gonadotropins. I. Normal menstrual cycle.

In an attempt to elucidate the effect of paramethasone acetate on the hormonal profile of the normal menstrual cycle, 5 clinically healthy women, aged 24-36 yr, with ovulatory cycles were studied during a control menstrual cycle and during treatment with paramethasone acetate (6 mg/day). The length of the untreated cycle was 29.2 +/- 2.3 days as compared to 29.0 +/- 3.1 days during the paramethasone-treated cycle. Peak plasma E-2 level was 188.2 +/- 42.1 pg/ml in the control cycle and 74.4 +/- 15.3 pg/ml during paramethasone treatment (P is less than 0.05). Peak plasma 17 OH-P was 4.0 +/- 0.4 ng/ml in the control cycle and 1.6 +/- 0.2 ng/ml during the paramethasone treated cycle (P is less than 0.005). No significant differences in plasma progesterone were observed during the luteal phase of both cycles. Minimal and scattered differences were observed in plasma FSH. However, plasma LH levels were lower in the paramethasone acetate than in the control cycle almost throughout the entire period of study. Furthermore, midcycle LH peak in the control cycle was 958 +/- 104 ng/ml as compared to 283 +/- 24 ng/ml during the paramethasone treatment (P is less than 0.005). Despite these differences, ovulation occurred during paramethasone treatment based upon the observed rise in BBT, the plasma progesterone levels above 6 ng/ml and the secretory changes in the endometrium. These results suggest that: 1) Paramethasone may block E-2 synthesis at the ovarian level and , 2) Ovulation may still occur even in the presence of E-2 and LH plasma concentrations lower than those occurring in the normal menstrual cycle.

Adult↗
PubMedDate not supplied

An in vitro biomechanical study of a multiplanar circular external fixator applied to equine third metacarpal bones.

The biomechanical characteristics of a 4-ring circular multiplanar fixator applied to equine third metacarpal bones with a 5 mm mid-diaphyseal osteotomy gap were studied. Smooth Steinmann pins, either 1/8 inch, 3/16 inch, or 1/4 inch, were driven through pilot holes in the bone in a crossed configuration and full pin fashion and fastened to the fixator rings using cannulated fixation bolts. The third metacarpal bone fixator constructs were tested in three different modes (cranial-caudal four-point bending, axial compression, and torsion). Loads of 2,000 N were applied in bending and axial compression tests and a load of 50 N x m was applied during testing in torsion. Fixator stiffness was determined by the slope of the load displacement curves. Three constructs for each pin size were tested in each mode. Comparisons between axial stiffness, bending stiffness, and torsional stiffness for each of the three different pin sizes were made using one-way analysis of variance. There was no visually apparent deformation or permanent damage to the fixator frame, and no third metacarpal bone failure in any of the tests. Plastic deformation occurred in the 1/8 inch pins during bending, compression, and torsion testing. The 3/16 inch and 1/4 inch pins elastically deformed in all testing modes. Mean (+/-SE) axial compressive stiffness for the 1/8 inch, 3/16 inch, and 1/4 inch pin fixator constructs was: 182 +/- 16 N/mm, 397 +/- 21 N/mm, and 566 +/- 8.7 N/mm; bending stiffness was 106 +/- 3.3 N/mm, 410 +/- 21 N/mm, and 548 +/- 12 N/mm; and torsional stiffness was 6.15 +/- 0.82 N x m/degree, 7.14 +/- 0.0 N x m/degree, and 11.9 +/- 1.0 N x m/degree respectively. For statically applied loads our results would indicate that a 4-ring fixator using two 1/4 inch pins per ring may not be stiff enough for repair of an unstable third metacarpal bone fracture in a 450 kg horse.

Animals↗
PubMedDate not supplied

[Retrograde jejuno-gastric invagination as a complication of gastric surgery].

A review of the world's medical literature concerning retrograde jejunal-gastric invagination reveals that it is a very unusual complication. It is sometimes seen following gastric surgery and presents with the clinical picture of a high intestinal occlusion. From the clinical point of view the diagnosis is difficult but the radiologic study with contrast medium is always useful. Nonetheless, thirty percent of the cases are diagnosed correctly only at autopsy. There are now 146 cases published in the literature and in all the etiologic factors are different from those observed in other types of invagination. Early diagnosis and treatment improve the prognosis and eliminate a fatal outcome, as is seen in the two cases herein presented.

Adult↗
PubMedDate not supplied

Purification and partial characterization of a chromate reductase from Bacillus.

A soluble NADH-dependent enzyme capable of reducing hexavalent chromium [Cr(VI)] to the trivalent form [Cr(III)] was purified from chromate-resistant Bacillus QC1-2. An enriched single protein band of 24 kDa was observed by SDS-PAGE following HPLC ion-exchange and size-exclusion procedures. In the latter step, the chromate reductase showed a molecular mass of 44 kDa, which suggested that the enzyme consists of two subunits of about 24 kDa. Purified chromate reductase displayed optimal activity at a temperature and pH of 37 degrees C and 7.0, respectively. The enzyme showed a Km of 0.35 mM for chromate and a Vmax of 50 nmol Cr(VI) reduced per minute per mg protein.

Bacillus↗
PubMedDate not supplied

Arsenic resistance determinants from environmental bacteria.

Arsenic resistance determinants from 42 environmental bacterial isolates (32 Gram negative) were analyzed by DNA: DNA hybridization using probes derived from Escherichia coli and Staphylococcus plasmid or chromosomal arsenic resistance (ars) genes. In colony hybridization assays, 11 and 1 Gram negative strains hybridized with the E. coli chromosome and plasmid probes, respectively. No hybridization was detected using a probe containing only the arsA (ATPase) gene from E. coli plasmid or with a Staphylococcus plasmid ars probe. From Southern hybridization tests of some of the positive strains it was concluded that homology to ars chromosomal genes occurred within chromosome regions, except in an E. coli isolate where hybridization occurred in both the chromosome and a 130-kb plasmid. Our results show that DNA sequences homologous to E. coli ars chromosomal genes are commonly present in the chromosomes of environmental arsenic-resistant Gram negative isolates.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Bacterial systems for expelling toxic metals].

Bacteria have developed diverse resistance strategies towards toxic metals with which they interact in the environment. The mechanisms of tolerance include extracellular precipitation, sequestration by cell envelopes, intracellular accumulation, redox transformations and membrane efflux systems. Genes responsible for these processes may be encoded by the chromosome or by plasmids. Since some toxic metals are also essential micronutrients (i.e. copper, cobalt, zinc, nickel), bacteria must precisely adjust the functioning of uptake and efflux systems to maintain their adequate intracellular levels. In the case of metals with no biological function (i.e. cadmium, silver), transport systems must be oriented only to the extrusion of the toxic ions. In the last few years, several bacterial systems devoted to the efflux of toxic metals were analyzed at the molecular level resulting in a detailed understanding of the biochemical mechanisms of resistance. Among these are the membrane pathways that extrude cations derived from copper, cadmium, zinc, nickel, cobalt and silver. Two general mechanisms have been found: those involving P-type ATPases, and some using proton antiporter systems.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Mechanisms of bacterial resistance to heavy metals].

Resistance to toxic heavy metals has been found in bacteria from clinical and environmental origins. The genetic determinants of resistance are frequently located on plasmids or transposons. Several heavy metal resistance genes have been cloned and sequenced. The mechanisms of resistance to heavy metals are commonly based on novel membrane transport systems that expel the toxic ions (including cobalt, nickel, zinc, and probably copper and chromium) from the bacterial cytoplasm. Arsenic and cadmium ions are effluxed from the cells by specific membrane ATPases encoded by resistance plasmids. Reduction of mercuric ions to the volatile metallic form by a plasmid-coded enzyme is responsible for mercury resistance. Studies on other resistance determinants (e.g., antimony, bismuth, boron, lead, silver, tin, tellurium) have been reported but the mechanisms of resistance are still unknown.

Bacteria↗
PubMedDate not supplied

[Chromates: resistance and detoxification in bacteria].

Derivatives of hexavalent chromium (chromates and dichromates) are highly toxic and have been shown to be mutagens and carcinogens. These compounds are often disposed to the environment as a result of diverse industrial procedures. The presence of chromates selects bacterial strains possessing chromate resistance determinants, commonly carried by plasmids. Some bacteria are able to reduce hexavalent chromium to trivalent chromium which is much less toxic. Bacterial strains combining both properties, resistance to and reduction of chromate, are potentially useful for decontamination of sewage or other refuse contaminated by chromates.

Amino Acid Sequence↗
PubMedDate not supplied

[Bacterial resistance to arsenic compounds].

Arsenic compounds, often present as environmental pollutants, are highly toxic for most microorganisms. Some microbial strains possess genetic determinants conferring resistance to arsenic derivatives. In bacteria, these determinants are usually located on plasmids, which has facilitated their analysis with molecular detail. Bacterial plasmids conferring arsenic resistance encode specific pumps that extrude arsenite (AsIII). In Gram-negative bacteria, the efflux pump consists of a complex formed by an ATPase (ArsA) associated with a membrane anion channel (ArsB). Arsenate (AsV) is converted to arsenite by a soluble reductase (ArsC). Proteins ArsB and ArsC, but not the ATPase, are also found in Gram-positive bacteria. Besides the widely spread plasmid arsenic resistance determinants, some bacteria possess the ability to enzimatically oxidize arsenite to less toxic arsenate.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Metal resistance systems in Pseudomonas].

Several chromosome- and plasmid-encoded metal resistance genetic systems have been studied in Pseudomonas and related bacteria. Some systems are known with molecular detail whereas others are still poorly understood. The former include resistance genes for cations derived from mercury, cadmium and copper and anions from arsenic and chromium. Except for mercury, where a redox transformation occurs, extrusion of the toxic ions from the bacterial cytoplasm appears to be the most common mechanism of resistance.

Alcaligenes↗