Role of fatty acid oxidation in mechanism of action of gastric secretagogues

The role of beta-oxidation in the mechanism of stimulation of acid secretion was examined in toad gastric mucosa in vitro. The incubation with 4-pentenoate selectively inhibited in a dose-dependent manner the rate of 14CO2 formation from [1-14C]octanoate. Pretreatment with 20 mM 4-pentenoate sharply reduced the respiratory and secretory responses to theophylline and histamine. Tracer studies showed a major utilization of exogenous octanoate over glucose and pyruvate by the in vitro toad gastric mucosa. Theophylline and histamine stimulated by 69% the rate of octanoate oxidation. Over 60% of the increments in oxygen uptake produced by theophylline and histamine accounted for the increments in octanoate oxidation, whereas glucose and pyruvate together accounted for less than 25%. Octanoate-dependent respiration was shown to correlate with octanoate oxidation under both inhibition with 4-pentenoate and stimulation with theophylline. Theophylline stimulated by 25% the rate of octanoate oxidation in Cl--free glucuronate-nutrient solutions. The present work provides further evidence for the primary role of fatty acid oxidation in the mechanism of acid secretion in amphibian.     

Utilization of a sol-gel method for encapsulation of doxorubicin

The sol-gel pre-doping method was used to encapsulate doxorubicin in silica gels and optimum conditions of preparation of drug-loaded gel were established, ensuring both reproducible and effective results of quantitative encapsulation of doxorubicin and its gradual but complete release. Doxorubicin was encapsulated in polysiloxane polymers using the method based on sol-gel encapsulation without a catalyst, with an acid catalyst (HCl) and a base catalyst (NH3). The time of gelation of the gel loaded with doxorubicin, encapsulation efficiency of the drug and the degree of release of the drug from the gel are all affected by the kind of catalyst (acidic or basic) or its absence at the gel preparation stage, and the temperature of the gelation process. The time of sol gelation when using the NH3 or HCl catalyst was 9 days at 21 degrees C, 2 days at 30 degrees C and 1.5 days at 37 degrees C, while for the gel prepared without a catalyst it was 90 days at 21 degrees C, 75 days at 30 degrees C and 70 days at 37 degrees C. The efficiency of doxorubicin encapsulation was 99.5 +/- 0.5% (w/w) for acid-catalyzed gel, 98.9 +/- 1.01% (w/w) for base-catalyzed gel and 86.4 +/- 11.6% (w/w) for non-catalyzed gel. A 100% (w/w) release of doxorubicin by diffusion through pores was found only in the case of base-catalyzed gel after a 140-h incubation time. For acid-catalyzed gel and non-catalyzed gel, the total amounts of released doxorubicin after 140 h of incubation were 3-5% (w/w) and 9-11% (w/w), respectively. The stability of doxorubicin encapsulated in the three kinds of gel matrices was found to be improved compared to the stability of a free form of the drug in solution.     

Architectural organisation of neuronal activity-associated magnetic fields: a hypothesis for memory

Despite intensive investigation into the mechanisms underlying the memory process, the physical bases for this superior cognitive function remain elusive. Neuronal activity-associated magnetic fields (NAAMFs) hypothesis of memory suggests that items of information are stored as three-dimensional bundles of magnetic fields associated to the complex but extremely organised cerebral cortex. The present paper proposes a plausible architectural organisation of neuronal activity-associated magnetic fields that may explain how information could be stored in the human cerebral cortex. Magnetic fields generated as consequence of neuronal minicolumns activation could modify the basal "electromagnetic status" of the closest astrocytes allowing codification and storage of information.     

PCR analysis of pulsed-field gel electrophoresis-purified plastid DNA,a sensitive tool to judge the hetero-/homoplastomic status of plastid transformants

The genetic transformation of plastids of higher plants has developed into a powerful approach for both basic research and biotechnology. Due to the high copy number of the plastid genome per plastid and per cell, repeated cycles of shoot regeneration under conditions selective for the modified plastid chromosome are required to obtain transformants entirely lacking wild-type plastid genomes. The presence of promiscuous plastid DNA in nuclear and/or mitochondrial genomes that generally contaminate even gradient-purified plastid fractions reduces the applicability of the highly sensitive PCR approach to monitor the absence of residual wild-type plastid chromosomes in transformed lines. It is therefore difficult, or even impossible, to assess reliably the hetero- or homoplastomic state of plastid transformants in this manner. By analysing wild-type and transplastomic mutants of tobacco, we demonstrate that separation of plastid chromosomes isolated from gradient-purified plastid fractions by pulsed-field gel electrophoresis can overcome the problem of (co)amplification of interfering promiscuous plastid DNA. PCR analyses with primers specific for plastid, mitochondrial and nuclear genes reveal an impressive purity of such plastid DNA fractions at a detection limit of less than one wild-type plastid chromosome copy per ten transplastomic cells.     

Digoxin dosing in the aged: new pharmacokinetic system versus Jellife and Koup methods

To evaluate three methods for digoxin dose adjustment in aged patients, we determined the plasma digoxin levels that would be attained in 87 aged patients with doses adjusted to the kidney function by means of three separate procedures. Mean patient age was: 79.0 +/- 6.3 years; creatinine clearance (Clc): 0.70 +/- 0.23 mL/Kg of lean body weight and minute; digoxinemia/dose ratio (RCpD): 0.421 +/- 0.237 Kg/L. The dose that would attain a digoxinemia of 1.2 ng/mL, calculating the elimination constant (K) and the volume of distribution (V) as linear functions of the Clc, so that K ranges between 0.173 and 0.462 days-1 and V between 4 and 10 L/Kg of lean body weight when the Clc varies from 0 to 110 mL/minute, was 2947 ng/Kg of lean body weight, coefficient of variation (CV): 25.2%. The digoxinemia that patients would have with this D, taking into account the individual RCpD, was 1.1 ng/mL, CV: 38.0%; with figures between 0.8 y 2.0 ng/mL and above 2.0 ng/mL in the 81.6% and the 0.0% of the patients (95% confidence intervals (95% CI): 72.2% to 88.4 and 0.0% to 4.6%), respectively. The precision and the bias were 0.43 and -0.06 ng/mL (95% CI: 0.38 to 0.48 and -0.16 to 0.03 ng/mL), respectively, and with this method the digoxinemia was not associated with the Clc. We concluded that the described method would lead to good results if digoxin has not been prescribed in order to control the cardiac frequency in the setting of auricular fibrilation.     

Molecular epidemiology of hepatitis B virus in Afro-Venezuelan populations

Summary.  Hepatitis B virus (HBV) infection among Venezuelan populations of African origin was analyzed. These populations exhibited lower HBV prevalence than the one found in the African continent. Sequence analysis of 6 isolates showed that 3 belonged to genotype F, while the 3 others were HBV genotype A. HBV genotype A was more common in the Afro-Venezuelan groups than in the general Venezuelan population. This might reflect the introduction of genotype A during the slavery period. The absence of the African genotype E among these isolates supports the hypothesis of a recent origin for this HBV genotype. HBV genotype F has already been introduced to these relatively isolated communities. Received February 18, 2002; accepted March 8, 2002 Published online July 22, 2002     

Blood concentrations of immunoglobulins in children with vitamin A deficiency

The object of this study is to measure the influence that vitamin A has upon seric concentrations of different isotypes of immunoglobulins (IgM, IgG, IgA) in children with a normal nutritional state or a slightly subnormal one, as well as that of patients with lower respiratory infections. Fifty two children were studied over a period of 24 months. Twenty eight of these were from an orphanage, while 24 were hospitalized, due to a low respiratory infection. The patients with lower respiratory infection showed normal average concentration of vitamin A, but under that of the orphanage (p less than 0.025). It was also observed that malnutrition influences the seric concentrations of immunoglobulins, which were higher in normal individuals; never the less, when this group show deficiency of vitamin A the serum concentration of IgM became lower in the orphanage, malnutrition children. In a similar way, a lowering of IgG was observed in patients with lower respiratory infections and vitamin A deficiency, while no alterations were found in the serum concentration of IgG in any of the groups studied with vitamin deficiency. It is concluded that the concentrations of vitamin A and the nutritional state modify serum values of IgM and IgG.     

Comparison of FDTD-calculated specific absorption rate in adults and children when using a mobile phone at 900 and 1800 MHz

In this paper, the specific absorption rate (SAR) in scaled human head models is analysed to study possible differences between SAR in the heads of adults and children and for assessment of compliance with the international safety guidelines, while using a mobile phone. The finite-difference time-domain method (FDTD) has been used for calculating SAR values for models of both children and adults, at 900 and 1800 MHz. Maximum 1 g averaged SAR (SAR1 g) and maximum 10 g averaged SAR (SAR10 g) have been calculated in adults and scaled head models for comparison and assessment of compliance with ANSI/IEEE and European guidelines. Results show that peak SAR1 g and peak SAR10 g all trend downwards with decreasing head size but as head size decreases, the percentage of energy absorbed in the brain increases. So, higher SAR in children's brains can be expected depending on whether the thickness of their skulls and surrounding tissues actually depends on age. The SAR in eyes of different sizes, as a critical organ, has also been studied and very similar distributions for the full size and the scaled models have been obtained. Standard limits can only be exceeded in the unpractical situation where the antenna is located at a very short distance in front of the eye.