Toxoplasma gondii: decreased resistance to intracellular bacteria in mice

The effect of sublethal inocula of Toxoplasma gondii on the course of listeriosis and salmonellosis in mice was investigated. Intravenous injection of T. gondii 24 hr after inoculation of Listeria monocytogenes increased mortality from 16% (L. monocytogenes alone) to 68% (L. monocytogenes + T. gondii) (P less than 0.001). Multiplication of L. monocytogenes in spleens also was increased significantly in mice given T. gondii. By 3 days after infection, mice that had received T. gondii and L. monocytogenes had approximately 10 times the number of L. monocytogenes per spleen compared to mice receiving L. monocytogenes alone. Similarly, mortality and the number of bacteria in spleens were increased in mice injected with Salmonella typhimurium and then inoculated with T. gondii. An in vitro assay of macrophage listeriacidal activity was used to investigate the mechanism of this decreased resistance. Peritoneal macrophages from mice injected with T. gondii were less bactericidal than macrophages from uninfected mice. Delayed hypersensitivity responses to L. monocytogenes antigen were markedly suppressed in mice injected with T. gondii. T. gondii infection appears to suppress both macrophage and T-lymphocyte function and may result in decreased resistance to infections caused by intracellular bacteria.     

Dexamethasone-sensitive and -insensitive responses during in vitro differentiation of Friend erythroleukemia cells

We have investigated the mechanism(s) by which dexamethasone inhibit DMSO-induced Friend erythroleukemia cell differentiation in vitro. In particular, we examined the effects of dexamethasone on (a) the early events of differentiation such as cell volume alterations and 'memory response' and (b) the onset of biochemical events associated with terminal erythroid cell differentiation. By analysing kinetics of commitment of Friend cells to terminal erythroid differentiation on a clonal basis, we have observed that dexamethasone inhibited the completion of the latent period (time elapsed prior to commitment) and impaired "memory" (ability to inducer-treated cells to continue differentiation after a discontinuous exposure to inducer). Treatment of Friend cells with dexamethasone did not prevent the occurrence of DMSO-induced alterations in cell volume. However, dexamethasone treatment prevented a series of biochemical events associated with terminal Friend cell differentiation. These include the decrease in the rate of both cytoplasmic and nuclear RNA synthesis as well as the induction of cytidine deaminase activity and hemoglobin synthesis. These data indicate that the dexamethasone-sensitive process(es) operate during the early stages of Friend cell differentiation and that they are responsible for the inhibition of terminal erythroid maturation. These dexamethasone-sensitive processes, however, appear to be different from those regulating cell volume alterations during the early steps of DMSO-induced Friend cell differentiation.     

Potassium movement during sodium-induced motility initiation in the rat caudal epididymal spermatozoa

The sodium-induced sperm motility initiation of the rat cauda epididymal sperm has been studied in different potassium concentrations. High K+ inhibited motility initiation. At a K+ concentration of 50 mM (concentration found in the rat cauda epididymidis), sperm motility was inhibited by 80%. K+ movement across the sperm membrane has been followed by using 86Rb+ as a marker for K+. When the 86Rb+ preloaded sperm were suspended in a sodium-free medium, there was a little efflux of 86Rb+. However, if they were suspended in a sodium-containing medium, the efflux rate was greatly increased. This increase in 86Rb+ efflux rate was associated with an initiation of sperm motility. Both 86Rb+ efflux and motility initiation were triggered by a K+ ionophore 18-crown-6 (2 X 10(-3)M). However, the ionophore-induced 86Rb+ efflux and motility initiation only occurred in the presence of extracellular Na+. Tetraethylammonium (TEA) chloride, which blocks K+ channels, inhibited motility initiation in a dose-dependent manner. Changes in the membrane potential of sperm have been followed using the fluorescent dye diO-C6-(3) whose fluorescence in sperm suspension changes markedly with changes in sperm membrane potential. During motility initiation, there was a fall in fluorescence of the dye due to increased partition into sperm cells. This observation may indicate a hyperpolarization of the sperm membrane during motility initiation. It was concluded that sperm motility initiation is associated with a complex ionic event. Na+ enters sperm cells in exchange with H+ and K+. This change in the permeability of the sperm membrane to ions is reflected by a change in the sperm membrane potential.     

The key role of residue 5 in angiotensin II

The conformation–biological activity relationships in a series of angiotensin II analogs substituted in position 5 were studied. Results indicated that only analogs with β-branched residue in position 5 possess spectral and biological properties identical to that of parent angiotensin II.     

Determination of nanogram quantities of osmium-labeled nucleic acids by stripping (inverse) voltammetry

Modification of nucleic acids with OSO4 in the presence of pyridine results in a formation of a covalently bound electroactive center in a polynucleotide chain detectable by polarographic (voltammetric) methods. It has been shown that DNA modified with osmium (DNA-Os) accumulates at the hanging mercury-drop electrode during a waiting time in a wide range of potentials between 0 and -1.0 V (against the saturated calomel electrode) and produce at neutral pH a well-developed reduction peak at about -1.2 V due to scanning in the cathodic direction. Using the differential-pulse stripping (inverse) voltammetry, nanogram quantities of single-stranded DNA-Os can be determined at relatively short waiting times (1-3 min). Double-stranded DNA is modified with osmium to a much lesser extent as compared to single-stranded polynucleotides. The degree of modification of double-helical DNA is influenced by the presence of single-stranded and distorted double-stranded regions in the DNA molecules and by the environmental conditions which influence the DNA conformation. Osmium can thus be used as a probe of the DNA structure, and a few micrograms of double-helical DNA sample suffice for the voltammetric analysis.     

The architecture of the animal fatty acid synthetase. III. Isolation and characterization of beta-ketoacyl reductase

Sequential treatment of the chicken liver fatty acid synthetase by trypsin and subtilisin cleaved the Mr 267,000 subunit to 6-8 polypeptides, ranging in molecular weights from 15,000 to 94,000. Fractionation of the digest by ammonium sulfate and chromatography on a Procion Red HE3B affinity column permitted the isolation of a polypeptide (Mr = 94,000) containing the beta-ketoacyl reductase activity but no other partial activities normally associated with the synthetase. The specific activity of the beta-ketoacyl reductase increased 2 to 3 times in this fraction, an increase that is within the expected range based on relative molecular weight. The kinetic parameters of this fraction towards NADPH and N-acetyl-S-acetoacetyl cysteamine were essentially the same as the beta-ketoacyl reductase component of the intact synthetase. However, the purified fragment did not catalyze the reduction of acetoacetyl-S-CoA derivative, a substrate that is readily reduced by the intact synthetase. Fluorescence measurements with etheno-NADP+ indicate the binding of about 1 mol of NADP+/94,000 daltons, a value which is in agreement with the results obtained from fluorescence measurements with NADPH and the binding of a radiolabeled photoaffinity analog of NADP+. Phenylglyoxal inhibits the beta-ketoacyl reductase activity of either the intact synthetase or the isolated fragment, suggesting the involvement of an essential arginine at or near the active site. Another fragment (Mr 36,000) containing beta-ketoacyl reductase activity was isolated from the synthetase after kallikrein/subtilisin double digestion. Previous mapping studies had shown that this fragment lies adjacent to the COOH-terminal thioesterase domain and overlaps the tryptic Mr 94,000 peptide by approximately 21 daltons. This fragment, but not the Mr 94,000 fragment, was found to contain the phosphopantetheine prosthetic group, indicating that the acyl carrier protein moiety is located in the 15,000-dalton segment that separates the beta-ketoacyl reductase from the thioesterase domain.     

Enhanced binding of radioligands to receptors of γ-aminobutyric acid and benzodiazepine by a new anticonvulsive agent,LY81067

A diaryltriazine, LY81067, effectively protects against pentylenetetrazole- and picrotoxin-induced convulsions in mice, with ED₅₀ values of 5.7 and 5.8 mg/kg i.p., respectively. LY81067 enhances the binding of both ³H-GABA and ³H-flunitrazepam to specific sites in rat brain membranes. The degree of enhancement by LY81067 varies from one brain region to another and is different for the binding of ³H-GABA and ³H-flunitrazepam. In cortical membranes, LY81067 increases the affinity of ³H-GABA for both high and low affinity sites and increases the number of sites. LY81067 increases the affinity of ³H-flunitrazepam for its binding sites without greatly increasing the number of sites. Like the pyrazolopyridines, the enhancement of ³H-flunitrazepam binding by LY81067 is dependent on chloride or related anions and is reversed by picrotoxin, suggesting that LY81067 exerts its anticonvulsant effects by binding to or near picrotoxin binding sites. The differential effects of LY81067 on the enhancements of ³H-GABA and ³H-flunitrazepam binding in several brain regions suggest extensive multiplicity of GABA/benzodiazepine/picrotoxin/anioin receptor complexes.     

Enhanced natriuretic effect of ADH in rats loaded with NaCl

ADH at doses 20 μU/100 g and 100 μU/100 g or 20 μU/100 g and 200 μU/100 g was injected intravenously into pentobarbital and alcohol anaesthetized rats loaded with either water or isotonic solution consisting of NaCl, glucose and ethanol. At the dose of 20 μU/100 g ADH retained water in both water and NaCl loaded animals. At high doses 100 μU/100 g in NaCl loaded rats and 200 μU/100 g in water loaded rats, ADH retained water and increased the renal excretion of Na⁺. That the natriuretic effect of ADH at the dose 20 μU/100 g was enhanced in NaCl loaded rats suggests that ADH is probably important in the regulation of Na⁺ content in the body when it is loaded with NaCl.     

Age-Related Changes in Aldehyde Dehydrogenase Activity of Rat Brain, Liver, and Heart

Abstract: Aldehyde dehydrogenase (ALDH) activity was measured in brains, livers, and hearts of 23–26-month-old and 3-month-old rats. A significant increase of ALDH activity was found in whole brain of old rats with both acetaldehyde (39%) and propionylaldehyde (15%) used as substrates. In different brain areas of old rats, with acetaldehyde used as substrate, a significant increase of ALDH activity was found in striatum (30–50%) and cerebral cortex (37%). However, no significant difference in ALDH activity was found in livers and hearts of young and old rats. Preliminary experiments showed a significant increase of aldehyde reductase activity (52%) with p -nitrobenzaldehyde used as substrate in whole brain of old rats compared with young rats. The present work indicates that an increase of ALDH activity in brain of old rats may be an adaptive phenomenon.     

Photosynthesis in Tall Fescue : IV. Carbon Assimilation Pattern in two Genotypes of Tall Fescue Differing in Net Photosynthesis Rates

We previously reported that the net photosynthetic rate of a decaploid genotype (I-16-2) of tall fescue (Festuca arundinacea Schreb.) was 32 to 41 versus 22 milligrams CO₂ per square decimeter per hour in a hexaploid genotype (V6-802) (Randall, Nelson, Asay Plant Physiol 59: 38-41). The high rate was later correlated with increases in total ribulose 1,5-bisphosphate carboxylase protein (17%) and activity (27%) (Joseph, Randall, Nelson Plant Physiol 68: 894-898). This report characterizes photosynthesis with respect to light saturation and early products of photosynthesis in an attempt to identify regulatory metabolic site(s) in these two genotypes. Analysis of the early products of photosynthesis indicated that both genotypes fixed CO₂ via the Calvin-Benson cycle with phosphoglyceric acid as the initial primary product. Both genotypes had similar ¹⁴C-labeled intermediates. Sucrose was the primary sink of ¹⁴CO₂ assimilation. After 10 min of ¹⁴CO₂ assimilation with attached leaves, sucrose accounted for 89% (decaploid) and 81% (hexaploid) of the total ¹⁴C incorporated. In 10 min, this amounted to 1.3 (decaploid) and 0.8 (hexaploid) μmol [¹⁴C]sucrose formed g fresh weight⁻¹ and reflected the observed differences in photosynthetic rates. There was limited labeling of starch (1%) and fructan (1%). Results of total nonstructural carbohydrates and P_i analysis also demonstrated sucrose was the predominant carbohydrate in fescue leaves. Quantitative differences in sucrose and P_i between the two genotypes may reflect changes in partitioning and this possibility is discussed.