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Biomedical subjects

G Diaz

Publications and source records attributed to G Diaz.

At least 37 records · Page 2Linked to original sources
PubMed1998

Contribution of HRTEM to the characterization of silica-incorporated copper-oxide catalysts prepared by the sol-gel technique.

The aim of the present work is a structural characterization study of silica-incorporated copper-oxide (CuO-SiO2) catalysts using HRTEM. The catalysts were prepared by the sol-gel synthetic route. Two calcined catalysts (at 400 degrees C and 800 degrees C, respectively) were analyzed before and after the "NOx + H2" catalytic reaction. It was found that in the 400 degrees C calcined catalyst, the copper is present as CuO crystallites in a structureless form, while in the 800 degrees C calcined catalyst, it was assumed that the copper is automatically dispersed into the silica matrix since no traces of crystalline copper were observed. Under a reducing atmosphere, i.e., after reaction, the former showed large crystallites of CuO, while in the latter a segregation of colloidal crystallites, a mixture of Cu2O and metallic Cu, was observed. It is worth noting that in the case of the 400 degrees C "after-reaction" catalyst, a change in color was observed after a few minutes of air exposure. This result suggested that the reduced copper-oxide phase obtained after reduction was unstable.

Catalysis↗
PubMed1998

Appetite suppression and weight loss after the cannabinoid antagonist SR 141716.

The effect of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight was assessed in adult, non-obese Wistar rats. The daily administration of SR 141716 (2.5 and 10 mg/kg; i.p.) reduced dose-dependently both food intake and body weight. Tolerance to the anorectic effect developed within 5 days; in contrast, body weight in SR 141716-treated rats remained markedly below that of vehicle-treated rats throughout the entire treatment period (14 days). The results suggest that brain cannabinoid receptors are involved in the regulation of appetite and body weight.

Animals↗
PubMed1998

Gamma-hydroxybutyric acid intake in ethanol-preferring sP and -nonpreferring sNP rats.

Gamma-hydroxybutyric acid (GHB) and ethanol share several pharmacological similarities, suggesting that GHB may exert ethanol-like effects in the central nervous system. The present study was designed to test whether selectively bred ethanol-preferring rats would, unlike ethanol-nonpreferring ones, self-administer GHB, consistent with their higher preference for ethanol. Male ethanol-naive Sardinian alcohol-preferring (sP) and Sardinian alcohol-nonpreferring (sNP) rats were used. In Experiment 1, GHB solution (1% (w/v) in water) was initially offered as the sole fluid available for 14 consecutive days and then presented under the two-bottle, free-choice regimen, one bottle containing water and the other the GHB solution, for an additional 14 consecutive days. During the free-choice phase, high preference for GHB and intake of pharmacologically relevant daily doses of GHB developed in both rat lines, presumably because the 14-day no-choice period would unmask the reinforcing properties of GHB and lead to acquisition of GHB preference also in the supposedly less susceptible sNP rats. In Experiment 2, the forced GHB drinking phase was reduced to 3 days. Under the subsequent free-choice regimen, daily GHB preference and intake were initially low in both sP and sNP rats; however, after approximately 10 days, GHB preference and intake in sP rats rose progressively and then stabilized to significantly higher levels than in sNP rats throughout the entire free-choice phase. It is likely that episodic binges of GHB intake occurring during the first 10 days resulted in experiencing the reinforcing properties of GHB by sP but not sNP rats. The results of the present study suggest that a) sP rats are genetically more sensitive to the reinforcing effects of both ethanol and GHB than sNP rats; and b) disclosure of the higher sensitivity of sP rats to the reinforcing effects of GHB is a function of the length of the induction procedure. The results are also discussed in terms of differences in GHB receptors contributing to the predisposition to ethanol preference and avoidance, respectively.

Alcohol Drinking↗
PubMed1998

Tamoxifen does not improve survival of patients with advanced hepatocellular carcinoma.

To discover whether tamoxifen is able to extend the survival of patients with advanced hepatocellular carcinoma, we included 80 patients with cirrhosis and advanced hepatocellular carcinoma in a multicenter, double-blind, placebo-controlled trial in order to analyze the influence of treatment with tamoxifen on survival. The patients were randomized to receive tamoxifen, 40 mg/day (group 1), or placebo (group 2). Both groups were similar in age, sex, etiology of cirrhosis, biochemical, hematologic and hormonal parameters, morphology of the tumor (nodular vs multinodular or massive), Child-Pugh's score, and Okuda's stage. The 1-year survival rate was similar in both groups (30% in group 1 vs 37.8% in group 2; p = 0.31). Tamoxifen treatment was well tolerated by the patients. We conclude that tamoxifen does not extend the survival of patients with cirrhosis and advanced hepatocellular carcinoma.

Adult↗
PubMed1997

Multicentric endobronchial smooth muscle tumors associated with the Epstein-Barr virus in an adult patient with the acquired immunodeficiency syndrome: a case report.

BACKGROUND: The incidence of benign and malignant smooth-muscle tumors (leiomyomas and leiomyosarcomas) is increased in children with the acquired immunodeficiency syndrome (AIDS). Epstein-Barr virus (EBV) infection has been implicated in the pathogenesis of these tumors. Smooth muscle tumors in adults with AIDS are extremely rare, with only six cases involving extrapulmonary sites reported in the literature. METHODS: Multifocal smooth walled endobronchial tumors were removed from a 35-year-old man with AIDS using rigid bronchoscopic laser resection. The tumor tissues were processed for routine histology, immunohistochemical stainings, and EBV in situ hybridization using an EBV-encoded RNA- 1 RNA oligonucleotide probe. RESULTS: Histologic features and immunohistochemical profiles were characteristic of smooth muscle tumors. EBV gene expression was detected in > 90% of tumor cell nuclei. Although overt histopathologic evidence of malignancy was lacking, some of the histopathologic findings, along with multifocality of the tumors and the rapid appearance of new tumors, suggested an unfavorable prognosis in this case. CONCLUSIONS: To the authors' knowledge, this is the first reported case of multicentric smooth muscle tumors involving the bronchi and lungs of an adult patient with AIDS. Diffuse EBV gene expression in the tumor tissue supports the hypothesis that EBV infection contributes to the pathogenesis of tumors of smooth muscle origin in immunocompromised hosts.

AIDS-Related Opportunistic Infections↗
PubMed1997

Chromatin pattern by variogram analysis.

Many cytological processes such as cell proliferation, differentiation, transformation, apoptosis, etc., are accompanied by specific chromatin changes, usually identified on the basis of the relative content of euchromatin and heterochromatin. In order to achieve a quantitative, non-subjective evaluation of the chromatin pattern, two different approaches may be undertaken, one consisting in the analysis of the several morphological features of chromatin grains (size, shape, density, arrangement, and distribution), and the second consisting in the analysis of the chromatin globally considered as a coherent texture. Although the second approach appears to be simpler and more suitable, methods of texture analysis--including those specifically designed for the analysis of the chromatin pattern--are rarely applied due mainly to the unsuitability of sampling procedures and the excessive crypticism of results. As an alternative to traditional texture analysis, we suggest a method supported by a sound mathematical theory and approximately 30 years of applications in the field of geostatistics. The method, called variogram, analyzes the intrinsic structure of data sampled at different distance intervals and directions, and outputs easily understandable results. Recently, variogram analysis has successfully been exported from geostatistics to other fields (for example, ecology and epidemiology) that make use of spatially referenced variables. Based on the fact that pixels represent a perfect array of data ordered at regular distance intervals and directions, the variogram can be adopted to explore nuclear images and recognize chromatin patterns. Variograms of different nuclei can be summarized by multivariate methods without the need of previous standardization of data. This allows comparison and discrimination of chromatin patterns from mixed cell populations. Preliminary data obtained from young neurons undergoing massive apoptosis reveal a self-consistent map of nuclear changes correlated to the degenerative process.

Animals↗
PubMed1997

Rapid mutagenesis and purification of phage RNA polymerases.

We have developed plasmid-based expression systems that encode modified forms of T7 RNA polymerase (RNAP) having 6-12 histidine residues fused to the amino terminus. The histidine-tagged RNAPs (His-T7 RNAPS) are indistinguishable from the wild-type (WT) enzyme in nearly all biochemical assays. Similar plasmids that encode His-tagged T3 and SP6 RNAPs have also been constructed. To facilitate site-directed mutagenesis of the RNAP gene, the size of the target plasmid was minimized by using T7 RNAP itself as a selectable marker. BL21 (DCAT4) cells (which carry a chromosomal copy of the chloramphenicol acetyltransferase cat gene under control of a T7 promoter) are resistant to chloramphenicol when functional T7 RNAP is expressed, thus allowing the selection and maintenance of the target plasmid in these cells. Mutagenesis is accomplished by denaturing the plasmid, annealing mutagenic DNA primers, and repairing the plasmid with T4 DNA polymerase. Two DNA primers are used: one corrects a defect in the bla gene, the other introduces the desired mutation into the RNAP gene; 30-85% of the ampicillin-resistant transformants carry the desired mutation in the RNAP gene. By using BL21 (DCAT4) cells as a recipient for transformation the functional integrity of the RNAP gene may conveniently be monitored by assessing the level of chloramphenicol resistance in vivo. Methods for rapid, simultaneous purification of multiple samples of modified (His-tagged) and conventional RNAPs are described. Together, these developments greatly enhance our ability to characterize this important class of enzymes.

Amino Acid Sequence↗
PubMed1997

Chronic morphine and naltrexone fail to modify mu-opioid receptor mRNA levels in the rat brain.

Previous radioligand-binding studies have reported conflicting results concerning the effect of chronic morphine administration on the regulation of mu-opioid receptor (MOR) density. On the other hand, chronic administration of an opioid antagonist, such as naltrexone, has been shown to increase the density of the MOR. In order to determine if the changes in the MOR are associated with alterations in receptor mRNA levels, we investigated MOR gene expression following chronic treatment with morphine and/or naltrexone. MOR mRNA levels, determined by the ribonuclease protection assay (RPA), were unchanged with respect to control during chronic morphine treatment and morphine withdrawal in each of the analysed brain areas. Furthermore, chronic administration of naltrexone did not result in changes of MOR mRNA levels in rat striatum of naive and morphine-dependent rats, suggesting that the up-regulation of the MOR density, at least in this tissue, is not regulated at transcriptional level.

Animals↗
PubMed1996

Age and weight relationship in Boophilus microplus (Ixodoidea: Ixodidae) larvae.

The study of the age of free-living stages of ticks is not a frequent subject in acarology research. Baseline knowledge and some possible applications both in research and in tick control are to be considered. Sixty engorged females were incubated at 28 +/- 1 degrees C and 100% relative humidity. Age zero of larvae was established at 10 days after the beginning of eclosion. Larvae were weighted in paper envelopes in groups ranging from 150 to 400 each. Live weight means (LWM) and dry weight means (DWM) were obtained. All larvae have defecated at age zero. Maximum survival was 57 days. Larval age was also expressed as effective temperature summings (ETS). LWM declines slightly with age. DWM has a linear relationship to age from 0 to 504 degrees C-day with a determination coefficient of 0.95. Absolute water content increases from 0 to 504 degrees C-day; further water content diminishes. Dry matter weight declines just to 504 degrees C-day of age. It might be theoretically possible to estimate the age of larvae in pasture by weighing groups of them.

Aging↗
PubMed1996

Nuclear pattern recognition by two-parameter texture analysis.

The present paper describes a simple procedure for the analysis of chromatin texture. High-resolution digitized images of nuclei are first standardized to render gray values invariant to staining and illumination conditions. Subsequently, the nucleus is subdivided by a square grid into 0.4 x 0.4 microns2 quadrats and standard deviations of gray values within each quadrat are estimated. Finally, the overall mean and standard deviation of quadrat standard deviations are calculated. These values may be considered as pure descriptors of the nuclear texture, as they represent the distribution of chromatin changes, disregarding any absolute densitometric and morphometric feature. Using the above descriptors it is possible to recognize at least seven chromatin patterns in a mixed population of developing and degenerating neurons. Results are visually verified by mapping the original pictures at the corresponding bivariate plot points. Comparison with the Markovian texture analysis is discussed.

Animals↗
PubMed1995

Oral self-administration of gamma-hydroxybutyric acid in the rat.

The present study describes the induction of gamma-hydroxybutyric acid (GHB) preference over water in rats. GHB solution (1% w/v in water) was initially offered as the sole fluid available for 14 consecutive days. Subsequently, rats were given a free choice of GHB solution and tap water for 20 consecutive weeks. Under the free-choice regimen, all rats showed periods of preference for GHB solution over water and periods of voluntary abstinence from GHB. On GHB-preference days, GHB was ingested at pharmacologically relevant doses. GHB intake occurred in 2-3 discrete episodes during the nocturnal phase. The development of an animal model of GHB self-administration may constitute a useful tool in the investigation of the neurobiological substrates of GHB-reinforcing properties.

Administration, Oral↗
PubMed1994

In vitro and in vivo activities of reduced-size antagonists of luteinizing hormone-releasing hormone.

A novel series of octapeptide LHRH antagonists was designed on the basis of the structure of the (2-9) fragment of a LHRH agonist. By adopting a systematic SAR study, we were able to improve first the in vitro activity and then the in vivo LH suppression, raising them up to the range of the decapeptide antagonists NalGlu (51) and A-75998 (50), resulting in A-76154 (49). The octapeptide antagonist A-76154 is the most potent reduced-size LHRH antagonist reported. It suppresses LH in the castrated rat by over 80% for a period of 4 h following sc bolus administration of 30 micrograms/kg.

Amino Acid Sequence↗
PubMed1993

Effect of N-methyl substitution of the peptide bonds in luteinizing hormone-releasing hormone agonists.

Each peptide bond in leuprolide (1), deslorelin (13), and nafarelin (24) was separately substituted with N-methyl. The synthesized compounds were tested for in vitro receptor binding, LH release, and stability against chymotrypsin and intestinal degradation. The NMe-Ser4 (30), NMe-Leu7 (33), and Sar10 (35) analogues of nafarelin had pD2 values 2-, 20-, 9-fold higher than their respective parent. All the other N-methyl agonists were less active. For the first time, conversion of LHRH agonists to antagonists was observed as a result of N-methyl substitution in the peptide backbone. [NMe-Phe2,DLeu6,Pro9NHEt]LHRH (4), [NMe-1Nal3,DLeu6,Pro9NHEt]LHRH (6), [NMe-His2,DTrp6,Pro9NHEt]LHRH (14), [NMe-Phe2,DNal6]LHRH (27), and [D2Nal6,NMe-Arg8]LHRH (34) exhibited antagonist responses. Substitutions of NMe-1Nal3, NMe-Ser4, or NMe-Tyr5 in leuprolide rendered the 3-4 peptide bond in these compounds completely stable to chymotrypsin. Examination of the three-dimensional structure of leuprolide when bound to the active site of chymotrypsin, reveals the NH's of residues 3 and 5 are involved in hydrogen bond interactions with the enzyme. N-Methylation at these positions is not only disrupting the hydrogen bond interactions, but is also sterically preventing the substrate from fitting in the enzyme's active site. All the compounds in the leuprolide series were also tested against intestinal degradation using an in vitro rat jejunum sac assay. In this model the pattern of stabilization was similar, but not identical, to that against chymotrypsin. The pharmacokinetics of all the analogues in the leuprolide series and of several others in the deslorelin and nafarelin series were determined. The clearance values of all the three NMe-Tyr5 analogues, 8, 20, and 31 were lower than their respective parents. These slower clearances suggest lower rates of metabolism.

Amino Acid Sequence↗