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PubMed1982

Effects of hexavalent chromium on the adenylate pool of hamster fibroblasts.

The mechanisms through which Cr(VI) reduces the intracellular levels of ATP in hamster fibroblasts (BHK 21 line) were investigated. Leakage of pool components during treatment of cells prelabelled with [3H]adenosine was examined. Adenylate pool composition was analyzed by thin-layer chromatography (TLC) in cells incubated with [3H]adenosine immediately after treatment with Cr(VI), and the endogenous concentrations of different nucleotides were determined by high-performance liquid chromatography (HPLC). Interference of Cr(VI) with different steps of ATP biosynthesis could be assessed. Treated cells showed increased loss of radioactive hypoxanthine and inosine in the treatment medium, but no nucleotides were detected outside the cells. A marked unbalance of the endogenous adenylate pool was produced by chromium, consisting in a strong decrease of ATP, accompanied by a very pronounced increase of ADP and AMP. Treatment with Cr(VI) caused an altered distribution of label among the different adenylate pool components, especially an accumulation of radioactivity in the ADP and AMP fractions. Also other effects on the soluble pool were detected by HPLC analysis, namely the reduction of NAD content and variations in the guanylate pool which closely paralleled the ones observed in the adenylate pool. Energy charge values, calculates on the basis of HPLC and TLC data, allowed to detect a specific inhibition of ADP phosphorylation to ATP. An interference with the early steps of adenylate synthesis could be inferred from the enhanced amounts of hypoxanthine and inosine in the treated cultures.

Adenine Nucleotides↗
PubMed1996

Effects of chromium(VI) on some ion-dependent ATPases in gills, kidney and intestine of a coastal teleost Periophthalmus dipes.

The coastal teleost species, Periophthalmus dipes, commonly known as the mudskipper, was exposed to three sublethal concentrations (5, 10 and 15 mg/l) of potassium chromate for three exposure durations (2, 4 and 6 days). The study compares the dose- and duration-dependent effects of Cr(VI), as potassium chromate, on the ATPase systems in various organs of this fish species. In this study, effects of Cr(VI) stress on total ATPase, (Na+,K+)-ATPase, (Ca+2)-ATPase, (Mg+2)-ATPase, (Ca+2, HCO3-)-ATPase and (Mg+2,HCO3-)-ATPase in gills, kidney and intestine were estimated. A general dose- and duration-dependent inhibitory trend was observed. However, it is evident that exposure duration is more important then dose in the inhibition of the activity of the enzymes. At some concentrations, initial stimulation of the activity of some enzymes were also noticed. However, maximum inhibition was observed in higher Cr(VI) concentrations exposed for the longest time. It is possible that this inhibition of the ATPases by Cr(VI) blocked the active transport system of the gill epithelial as well as chloride cells, glomerular and epithelial cells of the tubules and thus altered the osmoregulatory mechanism of the fish. It appears that this heavy metal ion alters the membrane permeability of the intestinal epithelial cells and other layer of cells by altering the activity of ATPases, resulting in a breakdown of the active transport mechanism needed for the absorption of nutrients, ions and metabolites.

Absorption↗
PubMed1991

Tin oxide coating of aluminous porcelain by reactive ion plating.

Alumina reinforced dental porcelain has been coated directly with tin oxide by reactive ion plating. Samples were prepared at different distances from the tin source in the ion plating rig. Tensile bond strengths of treated and untreated porcelain discs to a commercially available phosphate-methacrylate based dental cement were determined. Bond strengths of certain coated samples were found to be in excess of the cohesive strength of the porcelain substrates (greater than 7.8 MPa), whereas untreated porcelain achieved an average bond strength of only 3.4 MPa. The microstructures of coatings produced under conditions similar to those which yielded the maximum bond strength were examined in a scanning electron microscope and were found to be approximately 0.5 microns thick. It is believed that ion plating has great potential for rendering inert ceramic surfaces capable of direct bonding to dental cements.

Adhesives↗
PubMedDate not supplied

In-vivo evaluation of a feldspathic ceramic system: 2-year results.

OBJECTIVES: The aim of this clinical study was to evaluate feldspathic ceramic inlays by clinical criteria and quantitative margin analysis, and to compare clinical performance with the quantitative margin analysis results. METHODS: Fifty fibre-reinforced feldspathic ceramic inlays were placed in box-shaped, Class II preparations with all margins located in enamel. A low-viscosity type dual-curing resin luting material was used for luting. The inlays were evaluated clinically according to modified US Public Health Service criteria after 2 days, 1 year, and 2 years. In addition, quantitative margin analysis was performed under a scanning electron microscope using an image analysing system. RESULTS: Clinically the inlays performed very well after 2 years, showing no changes in colour, no recurrent caries and no marginal discolouration. Because of the wear of the composite resin luting material, margins were perceptible with an explorer in 54% of the cases after 2 years. Quantitative margin analysis showed significantly (P < or = 0.05) more marginal gaps at the composite/ceramic interface compared with the enamel/composite interface at each evaluation. There was a significant increase in marginal gaps at both interfaces during the first year, whereas marginal gaps at the composite/ceramic interface did not increase significantly during the second year. Quantitative margin analysis showed that both time and interface had a significant influence on marginal gaps. CONCLUSION: Quantitative margin analysis should be included in clinical long-term trials on this type of restoration to recognize possible deficiencies in ceramic, composite resin luting material, and the luting interfaces.

Adult↗
PubMed1996

Effects of thyroid hormone on the androgenic expression of KAP gene in mouse kidney.

The kidney androgen-regulated protein (KAP) gene exhibits a cell-specific hormonal regulation of its expression in the epithelial cells of proximal tubules of mouse kidney, where T3 is required for constitutive expression in the straight segments and androgens for expression in the convoluted ones. By using different models of hypothyroidism, we demonstrate that maximal androgen-mediated induction of the gene depends on thyroid hormone as well. This constitutes a specific event, since vitamin D3 cannot mimic the effects of T3, albeit their remarkable functional relationship. It is also shown that while congenital hypothyroid hyt/hyt male mice, exposed to maternal T3 in the gestational period, exhibit diminished but existent androgen-dependent cortical responses, mice exposed to goitrogens during gestation and postnatally are unable to express the gene even at postnatal day ninety. Impairment of KAP cortical expression in hypothyroid animals does not correlate with lower levels of androgens or androgen receptor expression.

Animals↗
PubMed1994

Diphenylene iodonium blocks K+ and Ca2+ currents in type I cells isolated from the neonatal rat carotid body.

Diphenylene iodonium (DPI), an inhibitor of NAD(P)H oxidase, blocks hypoxic excitation of the carotid body. We used the whole-cell patch-clamp technique to investigate the actions of DPI on ionic currents in isolated type I carotid body cells. DPI (10 microM) caused reversible blockade of K+ and Ca2+ currents in these cells, indicating that DPI is a non-selective ion channel blocker. Since hypoxic excitation of the carotid body is dependent on Ca2+ influx into type I cells, our observation that DPI blocks Ca2+ currents in type I cells can account for the ability of this compound to inhibit hypoxic excitation of the intact organ.

Animals↗
PubMed1996

Posttranslational regulation of nitrogenase activity by fixed nitrogen in Azotobacter chroococcum.

Using anti-(Fe protein) antibody raised against the Fe protein of the photosynthetic bacterium Rhodospirillum rubrum, it was found that the Fe protein component of nitrogenase (EC 1.18.2.1) from Azotobacter chroococcum cells subjected to an ammonium shock, and hence with an inactive nitrogenase, appeared as a doublet in Western blot analysis of cell extracts. The Fe protein incorporated [32P]phosphate and [3H]adenine in response to ammonium treatment, and L-methionine-DL-sulfoximine, an inhibitor of glutamine synthetase (L-glutamate: ammonia ligase (ADP forming), EC 6.3.1.2), prevented Fe protein from inhibition and radioisotope labelling. These results support that A. chroococcum Fe protein is most likely ADP-ribosylated in response to ammonium. After ammonium treatment, when in vivo activity was completely inhibited, Fe-protein modification was still increasing. This suggests the existence of another mechanism of nitrogenase inhibition faster than Fe-protein modification. When ammonium was intracellularly generated instead of being externally added, as occurs with the short-term nitrate inhibition of nitrogenase activity observed in A. chroococcum cells simultaneously fixing molecular nitrogen and assimilating nitrate, a covalent modification of the Fe protein was likewise demonstrated.

Adenosine Diphosphate Ribose↗
PubMed1993

Lipoprotein metabolism in the frog Rana esculenta.

1. The isoprenoid metabolism of the green frog has been studied, taking into consideration the transport and uptake mechanisms of plasma lipoproteins. 2. The lipoprotein complexes separated on KBr gradient showed six discrete peaks in both sexes. 3. The mechanisms of cellular uptake have been studied by immunological procedures. A molecule homologous to rat LDL receptor, and sharing its ability to bind only specific lipoproteins, has been shown. 4. Homology at mRNA level has also been demonstrated by Northern blot analysis and two different messengers have been shown in both male and female frog.

Animals↗
PubMed1985

Isoproterenol-sensitive adenylate cyclase in glomeruli isolated from young and adult rat renal cortex.

The stimulation of the adenylate cyclase activity of isolated rat renal glomeruli by isoproterenol decreased during kidney maturation. A potentiation of the isoproterenol response by GTP was demonstrated in young and adult animals. Both KF and GPP(NH)P enhanced the enzyme activity under basal conditions in young and adult glomeruli. GTP had no significant effect upon the basal activity of the adenylate cyclase in glomeruli of 14-day old rat kidney while it had one in 21-day old and adult kidneys.

Adenylyl Cyclases↗
PubMed1995

Effects of efonidipine hydrochloride (NZ-105), a calcium antagonist, on renal function in conscious spontaneously hypertensive rats.

1. We investigated the effects of short- and long-term administration of efonidipine hydrochloride (NZ-105), 1,4-dihydropyridine derivative, in conscious spontaneously hypertensive rats (SHR). 2. Oral administration of NZ-105 for 12 weeks caused diuretic and natriuretic effects, which were not attenuated during the experimental period. 3. In the short-term experiment for investigating the mechanism of the diuretic effect, intravenous injection of NZ-105 (0.03 mg/kg of body weight) significantly increased the urine volume (UV), renal plasma flow (RPF) and glomerular filtration rate (GFR). The increment rate of UV and RPF was 105.4 +/- 17.8% and 111.7 +/- 72.8%, respectively, which were larger than the increment rate of GFR (38.5 +/- 14.0%). 4. The diuretic or natriuretic effect of NZ-105 was suggested to be due to both the inhibition of sodium reabsorption and, at least in part, the increase of GFR.

Animals↗
PubMed1996

Myocardial and vascular effects of efonidipine in vitro as compared with nifedipine, verapamil and diltiazem.

1. Effects of efonidipine on isolated myocardial and aortic preparations were compared with those of nifedipine, verapamil and diltiazem. 2. All drugs produced concentration-dependent negative chronotropic effects on isolated guinea-pig atrial preparations. The potency order was efonidipine > or = nifedipine > diltiazem > or = verapamil, EC30 values being 3.08 x 10(-8)M, 3.48 x 10(-8)M, 1.27 x 10(-7)M and 1.47 x 10(-7)M, respectively. 3. Nifedipine, verapamil and diltiazem produced concentration-dependent negative inotropic effects on isolated guinea-pig left atrial preparations. The potency order was nifedipine > verapamil > diltiazem, EC30 values being 4.94 x 10(-8)M, 1.49 x 10(-7)M and 8.03 x 10(-7)M, respectively. Efonidipine, even at 1 microM produced no inotropic effect: 10 microM efonidipine decreased the contractile force by about 20%. 4. All drugs concentration-dependently attenuated the KCl-induced contraction of isolated rat aortic ring preparation. The potency order was nifedipine > efonidipine > verapamil > diltiazem, EC30 values being 2.98 x 10(-9)M, 1.24 x 10(-8)M, 3.96 x 10(-8)M and 2.13 x 10(-7)M, respectively. 5. Thus, efonidipine was demonstrated to be a potent vasodilator with negative chronotropic but minimal negative inotropic activity, which may be of benefit in the treatment of cardiovascular disorders.

Animals↗
PubMed1982

Organophosphate inhibition of avian salt gland Na, K-ATPase activity.

1. Adult black ducks (Anas rubripes) were given freshwater or saltwater (1.5% NaCl) for 11 days and half of each group was also given an organophosphate (17 p.p.m. fenthion) in the diet on days 6-11. 2. After 11 days, ducks drinking saltwater had lost more weight and had higher plasma Na and uric acid concentrations and osmolalities than birds drinking freshwater. 3. Saltwater treatment stimulated the salt gland to increased weight and Na, K-ATPase activity. 4. Fenthion generally reduced plasma and brain cholinesterase activity and depressed cholinesterase and Na, K-ATPase activities in salt glands of birds drinking saltwater.

Animals↗
PubMed1976

Histochemical fluorescence of tissue and brain monoamines: results in 18 minutes using the sucrose-phosphate-glyoxylic acid (SPG) method.

A rapid and sensitive modification of the glyoxylic acid method for the histofluorescent visualization of catecholamines and serotonin in mammalian brain, and other tissues, from cryostat sections is described. The procedure uses a phosphate-sucrose buffer solution combined with 1% glyoxylic acid. Tissues are reacted for 3 s at room temperature. Catecholaminergic cell bodies, pre-terminal, and terminal varicosities, well-localized and brightly fluorescent, are seen throughout cortical and subcortical structures. Serotoninergic cells show a weak fluorescence in rat and mouse brain but a strong fluorescence in dog and monkey brain.

Animals↗
PubMed1976

Evidence for central innervation of intracerebral blood vessels: local cerebral blood flow measurements and histofluorescence analysis by the sucrose-phosphate-glyoxylic acid (SPG) method.

Local cerebral blood flow using a hydrogen clearance technique and a histofluorescent modification of the glyoxylic acid method (SPG method) were used in rats to study the influence of brain stem centers on intracerebral flood flow. Recording of local cerebral blood flow following stimulation of the locus coeruleus but not of the ventrocaudal nucleus of the lateral lemniscus showed a significant blood flow decrease in anterior brain regions where innervation of ascending adrenergic pathways are known to occur. Adrenergic innervation using the SPG method (sucrose-potassium phosphate-glyoxylic acid) histofluorescence could not be verified in the rat but was evident in the dog and rhesus monkey brain sections examined. The results provide additional evidence suggestive of a role for the locus coeruleus in modulating or controlling intracerebral blood flow in these animals. In addition, histofluorescent visualization of intracerebral vessels in dog and monkey show an association between adrenergic varicosities and arterioles in bilaterally ganglion-ectomized animals. This adrenergic-vascular association was not seen in the rat. The results provide further evidence that central adrenergic innervation from the brain stem may control intracerebral blood flow independent of sympathetic influence.

Adrenergic Fibers↗
PubMed1986

Pre- and postsynaptic actions of noradrenaline and clonidine on myenteric neurons.

alpha-2 adrenergic agonists inhibit nicotinic excitatory postsynaptic potentials and reduce calcium dependent action potentials in myenteric neurons. To test the hypothesis that adrenergic inhibitory effects on action potential configuration and on inhibition of acetylcholine release from the nerve terminal are analogous processes, the pharmacological characteristics and underlying mechanisms of these two effects were compared in neurons of the myenteric plexus in the guinea pig. Both clonidine and noradrenaline reduced the nicotinic fast excitatory postsynaptic potential in a concentration dependent manner, although the maximum effect produced by noradrenaline was greater. The specific alpha-2 antagonist RX781094 blocked the action of noradrenaline, with an apparent Kd value of 3.8 +/- 1 nM. Clonidine was similarly antagonized by low concentrations of this compound. The potassium channel blocker barium prevented inhibition of the fast excitatory postsynaptic potential by clonidine but not by noradrenaline. Action potentials recorded from after-hyperpolarization neurons with cesium chloride filled electrodes were prolonged in duration due to the blockade by cesium of outward potassium movement. Under these conditions, noradrenaline reduced action potential duration and slowed the rate of rise of the calcium dependent component in the presence of tetrodotoxin. RX781094 antagonized the latter effect with an estimated apparent Kd of 5.8 +/- nM. The rate of rise of the calcium dependent action potential was not affected by clonidine (30 nM to 1 microM). In the absence of potassium channel blockers noradrenaline caused hyperpolarizations which were blocked by RX781094. It has been previously shown that clonidine hyperpolarizes myenteric neurons via an adrenergically mediated increase in potassium conductance. It was concluded that the characteristics of presynaptic inhibition of release by noradrenaline and clonidine parallel the respective actions of these agonists on action potential configuration. While all clonidine effects could be explained on the basis of an increase in potassium conductance, noradrenaline exerted an additional inhibitory action which persisted in the presence of potassium channel blockade by barium or cesium.

Action Potentials↗
PubMed1995

Fos activation in cultured tyrosine hydroxylase and oxytocin immunoreactive neurons.

Fos and other immediate early gene products are used as markers for neuronal activity. We identified Fos immunocytochemically after KCI-induced depolarization of cultured hypothalamic neurons. Five-day cultures were treated for 1 h with 50 mM KCI or media and fixed at 0, 0.5, 1, 2, and 4 h posttreatment. Sequential immunocytochemistry was performed to identify Fos immunoreactivity in tyrosine hydroxylase (TH)-immunoreactive (-ir) or oxytocin (OT)-ir neurons. Activated neurons [brown cells (TH-ir or OT-ir) with purple nuclei (Fos-ir)] were counted microscopically. KCI treatment resulted in an increased percentage of Fos-ir TH-ir and OT-ir neurons over control levels over the time course examined. Fos-ir peaked in TH-ir neurons at 0.5 to 1 h posttreatment, with levels returning to baseline at 4 h. Fos-ir in OT-ir neurons peaked at 2 h, and remained elevated at 4 h, showing prolonged activation. These results demonstrate that KCI-induced depolarization of cultured hypothalamic neurons increases Fos with a different time course in TH-ir vs. OT-ir neurons.

Animals↗
PubMed1982

Hexavalent chromium and ascorbic acid interaction on proliferation of the human cell line NHIK3025.

When cells from the human cell line NHIK3025 were cultured for 4 days, with hexavalent chromium (K2Cr2O7) at a concentration of 8 . 10(-7)M, the relative cell number was reduced to 38%. This effect of hexavalent chromium was abolished if ascorbic acid and chromate were added simultaneously to the incubation medium, but not if ascorbic acid was added 24 h prior to chromate addition. Dehydroascorbic acid was not able to reduce the effect of K2Cr2O7 either when added simultaneously or when added 24 h prior to chromate exposure. Therefore, the cells could only be protected against the toxic effect of hexavalent chromium when ascorbic acid was added at the same time as K2Cr2O7.

Ascorbic Acid↗
PubMed1991

Simple high-performance liquid chromatographic method for the determination of PGT/1A, a new immunostimulating drug, in biological fluids.

This paper describes a simple high-performance liquid chromatographic method for the determination of PGT/1A (3-L-pyroglutamyl-L-thiazolidine-4-carboxylic acid), a new immunostimulating drug, in plasma and urine. The column was packed with LiChrospher-NH2 (5 microns), the mobile phase was 0.02 M monobasic potassium phosphate (pH 3.2 with concentrated phosphoric acid)-acetonitrile (25:75, v/v), the flow-rate was 1.2 ml/min, the detection wavelength was 210 nm and the apparatus was a Varian Model 5000. Plasma (1 ml) was added to 1.2 ml of acetonitrile and the supernatant injected; the urine was diluted 1:5. The retention time of PGT/1A was 9.4 min in plasma and 9.9 min in urine. The method was validated for recovery, accuracy and reproducibility. The results after intravenous injection in twelve volunteers are also given.

Acetonitriles↗