Effect of ethanol on synaptosomal (Na+ + K+)-ATPase in control and ethanol-dependent rats

Rats were made dependent upon ethanol by feeding them liquid diets containing ethanol. Synaptosomal plasma membranes (SPM) were isolated from cerebral cortex and midbrain regions of isocaloric-fed control and ethanol-dependent rats. No major alcohol-induced alteration in in vitro (Na+ + K+)-ATPase activity was found in SPM of either brain area. At 37 degrees C, ethanol (0.10 to 0.98 M) added to incubations caused a dose-dependent inhibition of (Na+ + K+)-ATPase activity. The degree of inhibition found was independent of the diet administered or whether ethanol was present in the diet. At temperatures between 14 and 22 degrees C, 0.48 M ethanol caused a temperature-dependent decrease in activity. Arrhenius plots for SPM (Na+ + K+)-ATPase showed that in control and ethanol-dependent rats fed the Lieber de Carli diet, 0.48 M ethanol did not alter the transition temperature of this enzyme. Activation energies both above and below the transition temperature were decreased by the addition of ethanol to incubations. These results indicate that (Na+ + K+)-ATPase, a membrane-bound enzyme that is sensitive to its lipid environment and to the presence of ethanol, is not altered by the chronic administration of ethanol to rats.     

The inter-relationship between the age of carrot roots at harvest and infection by Mycocentrospora acerina in storage

Infection of carrot roots by Mycocenlrospora acerina in chill storage (3.5 °C) following inoculation with chlamydospores was studied in 1973–74 and 1974–75. AREAS of intact periderm were only rarely infected, and the high level of periderm resistance predominated over other variables. However, wound infection tended to increase with depth of wound and with increasing age of the plants at harvest. Irrespective of age of root or depth of wound, roots were comparatively resistant to infection at harvest and early in storage, resistance being expressed as a restriction of mycelial growth on the wound surface or localisation of the lesion. Increasing susceptibility with time in storage, depth of wounds, or age at harvest, resulted in larger numbers of inoculated sites becoming infected and a more rapid development from localised to progressive lesions.     

The motion of the left ventricle—III

We use the concept of a layered wall, where each separate layer is to be homogeneous, isotropic, and incompressible, to derive stress-strain relations for the middle layer muscle ring at the transverse midsection of the left ventricle; a convenient method of formulation is that based on the elastic potential function. The hoop or circumferential stress in all three layers is found using dimensional and mechanical parameters derived earlier. The various parameters are expressed as Fourier series so that their behavior over a complete ventricular cycle is known analytically. The cases of simple elongation and what we termcurvilinear simple elongation are considered for the middle layer muscle ring strain, and the resulting stress-strain relations are derived. The results are compared with an incompressible rubber-like material known as a Mooney material.     

Preparation of oxygen-18-labeled lipoxygenase metabolites of arachidonic acid

Plasma pseudocholinesterase and porcine liver esterase were used to catalyse the incorporation of the stable isotope oxygen-18 into the carboxyl moiety of lipoxygenase metabolites of arachidonic acid. This simple method produces eicosanoid products containing two oxygen-18 atoms; but the enzymes studied were found to display large substrate specificity in the efficiencies at which oxygen-18 could be incorporated into the lipoxygenase metabolites. Furthermore, [18O2]LTB4 was found not to back exchange during in vitro incubation with human neutrophils. The methods involved for stable isotope incorporation are simple, efficient and produce highly enriched species in a short time. By varying the type of esterase, the amount of esterase or the length of incubation highly enriched species of all eicosanoids tested could be prepared.     

Intrathymic implants of genetically modified fibroblasts.

Implantation of autologous rodent fibroblasts genetically altered to express human growth hormone has recently been shown to be a feasible approach to the delivery of new gene products in somatic gene therapy. However, the novel gene product elicited in its recipients an intense antibody response that would have curtailed the effectiveness of such therapy. The possibility of inducing tolerance to foreign gene product was explored by implanting allogeneic fibroblasts transfected with the human growth hormone gene into rat thymus, a site recently shown to be immunologically privileged and able to induce donor-specific tolerance to transplanted tissues. In the circulation of the implanted rats, human growth hormone was detected at 4-15 ng/ml serum within the first day and subsided to 0.6-9 ng/ml within the first wk in all animals implanted either thymically or intraperitoneally. Within 2-3 wk, high titers of anti-human growth hormone were detected in all animals regardless of the site of implantation. The failure of the thymus to offer immune protection for the foreign antigen was further confirmed when the animals were subsequently challenged with purified human growth hormone. An immediate twofold increase in titer within the first week of challenge was detected in animals previously implanted thymically. In contrast, animals implanted intraperitoneally but treated with short-term daily injection of cyclosporine A (28-41 days) did not mount any significant antibody response to human growth hormone throughout the experiment or even when challenged subsequently at weeks 8-10 with purified growth hormone. In conclusion, implantation of genetically modified fibroblasts in the thymus does not lead to tolerization toward soluble novel gene product secreted by these cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Negative skewness and negative correlations in spatial competition models

We consider a population of identical biological entities that compete with each other for space and derive, under rather weak assumptions, some statistical properties of the sizes (e.g. biomasses) of the individuals. It is proved, for example, that, during the early stages of competition, their size distribution becomes negatively skewed and the sizes of neighbouring individuals become negatively correlated. The results are proved for a regular periodic array of centres of the individuals where they can be compared with data on plantations.