PubMed Health⌕ Search

Biomedical subjects

F Chávez

Publications and source records attributed to F Chávez.

11 recordsLinked to original sources
PubMed2000

Compartmentalized reaction-diffusion systems.

Reaction-diffusion systems consisting of a collection of reactive domains separated by chemically inactive regions are considered. The reactive dynamics is governed by a multistep reaction mechanism and each reactive domain is specific to a particular elementary step or collection of elementary steps of the global reaction mechanism. Far-from-equilibrium situations where the global kinetics can give rise to complex states such as bistability or oscillations are studied. A general method for the calculation of the average concentration on each reactive domain is presented. The effects of compartmentalization are illustrated by a study of the influence of diffusion, reactive domain size, and domain distribution on the nature of the stationary states of the Schlögl model. Compartmentalization can drive the system into and out of the bistable regime of this reactive system.

Journal Article↗
PubMed1995

[Proliferating cell nuclear antigen in cervical cancer and precursor lesions].

The aim of this study was to study the degree of cellular proliferation quantifying the immunohistochemical expression of the proliferating cell nuclear antigen. We assessed paraffin embedded samples of 25 infiltrating epidermoid cervical carcinomas, 76 precursor lesions (34 of low and 42 of high grade), 29 normal and 13 metaplastic epidermoid epithelia. Mean values of proliferating cell nuclear antigen expression were 13.7% in normal epithelia, 15.7% in epidermoid metaplasia, 37.1% in low grade precursor lesions (35.3% in condilomas and 38.8% in mild dysplasia), 48.7% in high grade lesions (47.9% in moderate dysplasias, 50.5% in severe dysplasias and 50% in carcinoma in situ) and 54.7% in infiltrating carcinoma. There were differences in proliferating cell nuclear antigen expression nd mitotic index between low grade precursor lesions and high grade lesions and infiltrating carcinoma. No correlation was observed between mitotic index and proliferating cell nuclear antigen expression. We conclude that infiltrating epidermoid cervical carcinoma and its precursor lesions have a high level of proliferative activity, demonstrated by a high percentage of cells in active phases of the cellular cycle.

Carcinoma, Squamous Cell↗
PubMed1994

[Immunohistochemical expression of epidermal growth factor receptor (EGFR) in epidermoid carcinoma of the cervix uteri and its precursor lesions].

The epidermal growth factor receptor (EGFR) immunohistochemical expression was determined in 24 histological samples of squamous cell carcinoma of the cervix, 81 cervical squamous intraepithelial lesions (47 low-grade and 34 high grade), 20 normal squamous epithelia, 11 squamous mature metaplasias and 14 cervical adenocarcinomas. In 30 cases, it was determined by means in situ hybridization the presence of Human Papillomaviruses 6/11, 16/18 and 31/33/35. The immunohistochemical EGFR expression was higher in high-grade epithelial lesions (64.7%), particularly moderate dysplasia (72.2%), than in low-grade lesions (44.7%) and squamous carcinoma (45.8%), with significance differences only between high-grade lesions and normal squamous epithelia (p < 0.02). There were not EGFR expression differences between cervical squamous carcinoma (45.8%) and adenocarcinoma (42.9%). These findings suggest that the elevated expression of EGFR may be linked, at least initially, to the malignant state of the cervical squamous epithelia. On the other hand, the higher presence of HPV 16/18 than other HPV types in EGFR positive lesions, indicates some association between both factors.

Adenocarcinoma↗
PubMed1990

Pharmacokinetics of sulfamethoxazole and trimethoprim in Mexicans: bioequivalence of two oral formulations (URO-TS D and Bactrim F).

Two oral pharmaceutical formulations (URO-TS D and Bactrim F) containing 800 mg of sulfamethoxazole (SMZ) and 160 mg of trimethoprim (TMP) were given to 10 Mexican healthy volunteers, following a randomized cross-over design. Blood and urine samples were obtained, concentrations of TMP, SMZ, and its metabolite N4-acetyl SMZ were measured by HPLC and pharmacokinetic analyses were performed. The observed Cmax, tmax, half-life, AUC, and cumulative urinary excretion values for the three compounds studied were within the ranges that have been previously reported for European and North American subjects. Therefore, it appears that pharmacokinetics of SMZ and TMP in Mexicans are similar to those observed in Caucasian populations. When the two studied formulations were compared, no statistically significant differences were detected in any pharmacokinetic parameter. Therefore, it is concluded that both brands tested are bioequivalent. Moreover, these two formulations manufactured in Mexico yield SMZ and TMP plasma and urine levels similar to those obtained with equivalent formulations of European or North American origin.

Adult↗
PubMed1989

Pharmacokinetics of oral nifedipine: relevance of the distribution phase.

Pharmacokinetics of oral Nifedipine was studied in 12 Mexican young healthy volunteers, six men and six women, who received a 10 mg capsule. Plasma levels were determined by a nifedipine specific HPLC assay. Experimental data were fitted and pharmacokinetic parameters were calculated using an open two compartment model. No statistically significant difference was detected between men and women, thus both sexes were considered as a single population. Nifedipine plasma levels rose rapidly (ka = 8.46 +/- 1.96 h-1) reaching a maximum concentration of 145 +/- 23 ng/ml in 0.61 +/- 0.07 h. Plasma levels then decayed with a distribution phase (alpha = 1.98 +/- 0.40 h-1, t1/2 alpha = 0.46 +/- 0.06 h) and a terminal elimination phase (beta = 0.17 +/- 0.03 h-1, t1/2 beta = 4.98 +/- 0.55 h). AUC was 384 +/- 41 ng h/ml. Values of AUC and t1/2 beta were higher than those reported by other authors. Differences in the AUC could be due to ethnic origin, environmental factors or nutritional habits. Ten subjects presented plasma concentration-time curves in which the distribution phase was clearly distinguishable, having a ka/alpha relationship higher than 1.5. For the other two subjects, the distribution phase was not apparent and ka/alpha was lower than 1.5. The results show that an adequate characterization of the distribution phase is required if one pretends to use pharmacokinetic data for dosage regimen design.

Administration, Oral↗
PubMed1989

Pharmacokinetics of nifedipine slow release tablet in Mexican subjects: further evidence for an oxidation polymorphism.

Nifedipine kinetics after ingestion of 20 mg slow release tablets were studied in 12 young, healthy, Mexican subjects. Plasma levels were determined by a nifedipine-specific HPLC assay. Levels rose after drug administration reaching a maximum concentration of 48.7 +/- 7.3 ng/ml in 2.1 +/- 0.7 h (mean +/- SEM). Concentrations then decayed with a terminal half-life of 16.9 +/- 3.1 hours. AUC was 526 +/- 62 ng h/ml. Five individuals were fast and seven were slow nifedipine metabolizers, according to the AUC criterion proposed by Kleinbloesem and coworkers. Individual AUC/Dose values from this and from other two studies on oral nifedipine kinetics in Mexicans were cumulated and the frequency histogram and probit analyses were performed (N = 30). A bimodal distribution was clearly observed. Fast and slow metabolizers were distinguished as those subjects with AUC/Dose values either lower or higher than 22.5 ng h/ml mg. Unlike European populations, it appears that slow metabolization is more frequent in Mexicans. Data strongly support the hypothesis of the existence of a polymorphism concerning nifedipine disposition kinetics due to genetic basis.

Adult↗
PubMed1979

Pregnancy in patients with autoimmune thrombocytopenic purpura.

The obstetric and hematologic problems in 21 pregnancies of 18 patients with ATP are analyzed: one maternal and one fetal death occurred. Urinary estriol and oxytocinase were measured. Eighteen infants were born by vaginal delivery and three by cesarean section. None of the 20 liveborn infants died, but they had NIP due to the passage of maternal antibodies to the fetus. These results are compared to those reported in previous publications. The obstetric management of these patients should be individualized and carefully planned; it should not be based on the platelet count.

Female↗
PubMedDate not supplied

[Effects of avocado on the level of blood lipids in patients with phenotype II and IV dyslipidemias].

To examine the effects of avocado on plasma lipid concentrations a two-diet trial involving 8 phenotype IV and 8 phenotype II dyslipidemia patients was carried out. A diet rich in monounsaturated fatty acids (DRCA) using the avocado as their major source (30% of the total calories were consumed as fat, 75% of the total fat from the avocado), with restriction of saturated fat and less of 300 mg of cholesterol per day was evaluated. Patients also were in a low-saturated fat diet without avocado (DRSA). The three daily meals were eaten at our clinical unit. Diets were four weeks in duration and they were assigned in a crossover design. In phenotype II both DRCA and DRSA significantly reduced total cholesterol and LDL-cholesterol levels. On phenotype IV DRCA produced a mild reduction on triglyceride levels while DRSA increased them. On HDL-cholesterol concentrations DRCA produced a significant increase in both phenotypes while DRSA did it only in phenotype IV. Avocado is an excellent source of monounsaturated fatty acids in diets designed to treat hypercholesterolemia with some advantages over low-fat diets with a greater amount of carbohydrates.

Aged↗