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PubMed1982

The action of chromium on serum lipids and on atherosclerosis in cholesterol-fed rabbits.

Eight rabbits, fed on a 1% cholesterol diet for 30 days, were injected daily with potassium chromate for a further 60 days. A 50% reduction in aortic intimal plaque area and in aortic total cholesterol content was observed. However, although levels of serum cholesterol and triglycerides were consistently lower and levels of high density lipoprotein fractions consistently higher in the chromium-treated as compared to the control rabbits, these differences did not reach statistical significance. A further 6 rabbits were injected with potassium chromate and fed on a 1% cholesterol diet for 12 weeks. Mean aortic cholesterol content (+/-SEM) was 40.23 mg/10 cm aortic length (+/-7.50) as compared to 66.24 mg/10 cm (+/- 7.89) in a control group (P less than 0.05), whereas the area of aortic intima covered by macroscopic plaques was 67.5% (+/-2.79) and 81.1% (+/-3.14) (P less than 0.01) respectively.

Animals↗
PubMed1982

The effect of chromium on cholesterol-induced atherosclerosis in rabbits.

Rabbits fed on a 1% cholesterol diet for 30 days were injected daily with potassium chromate for a further 60 days. A 50% reduction in aortic intimal plaque area and in aortic total cholesterol content was observed. Control rabbits treated with chromium showed a significant increase in the chromium concentration of their aortas, liver and kidneys but not of the myocardium. Cholesterol-fed rabbits treated with chromium showed a significant increase in chromium concentrations in the liver and kidneys only. Serum cholesterol levels were consistently lower in the chromium-treated animals, although the differences did not reach significant levels.

Animals↗
PubMed1986

Effects of potassium chromate on atherosclerosis prevention and regression in rabbits.

The effect of intraperitoneal injections of potassium chromate on prevention and regression of atherosclerosis was observed in New Zealand White rabbits. In rabbits fed a 1% cholesterol diet for 90 days, potassium chromate injection was not associated with a significant difference in weight, serum cholesterol, total cholesterol content per 8.5 cm aorta, cholesterol content per gram of aorta or percent intima covered with plaque compared to controls. Similarly, significant differences were not seen in rabbits fed a 1% cholesterol diet for 90 days followed by 60 days of potassium chromate or distilled water injections and a standard diet. These results are in keeping with recent studies suggesting a more limited role for chromium in a variety of lipid-related disorders.

Animals↗
PubMed1994

An adaptable head retention and alignment device for computed tomography scanning of Macaca mulatta.

An adaptable retention device has been developed for the purpose of holding and aligning the head of a sedated primate subject during computed tomography (CT) scan procedures. The device is used to obtain a close reproduction of CT scan studies at a time before and after dental implant placement in the mandibles of nine subjects. Geometric and material properties are extracted from these studies for the purpose of developing finite elements computer models. The device is constructed of low-density acrylic and consists of a horizontal base to which lateral supports are affixed. The device is placed on the CT table and axially aligned with the scan beam. Repeatable, calibrated CT studies of primate implant subjects were possible using the head holding device.

Acrylic Resins↗
PubMed1994

Liquid-liquid extraction of a recombinant protein, cytochrome b5, with aqueous two-phase systems of polyethylene glycol and potassium phosphate salts.

The partitioning of cytochrome b5 in aqueous two-phase systems of polyethylene glycol (PEG) and potassium phosphate salts was investigated. Cytochrome b5 partitioning is enhanced with decreasing polymer molecular mass and with increasing tieline length and pH. The effect of cytochrome b5 mutation, by substitution of the glutamic acid at positions 56 and 92 of the polypeptide chain by a lysine, on protein partitioning was also studied. Partitioning of cytochrome b5 mutants shows the same dependence on tieline length and pH, following the order cytochrome b5 > mutant 56 > mutant 92.

Animals↗
PubMed1994

Polyethylene glycol-potassium phosphate aqueous two-phase systems. Insertion of short peptide units into a protein and its effects on partitioning.

Two different tetrapeptides, AlaTrpTrpPro and AlaIleIlePro, were inserted near the C-terminus of the protein ZZT0. The Trp-rich peptide unit strongly increased both the partitioning of ZZT0 into the polyethylene glycol (PEG)-rich phase in a PEG-potassium phosphate aqueous two-phase system and its retention on PEG and propyl hydrophobic interaction chromatographic columns with potassium phosphate as eluent. Both the partitioning and the retention increased with increasing number of Trp-rich peptide units inserted into ZZT0. Insertion of Ile-rich tetrapeptide units affected the partitioning and retention to a much lesser extent. Partition data also indicated a folding of inserted Trp tetrapeptides units, probably to minimize their water contact.

Amino Acid Sequence↗
PubMed1985

A simple method for the solubilisation of reduced NBT, and its use as a colorimetric assay for activation of human macrophages by gamma-interferon.

We describe a simple method by which the insoluble blue formazan dye produced by the reduction of nitro blue tetrazolium can be dissolved without heating using potassium hydroxide and dimethyl sulphoxide. This modification enhances the sensitivity and increases the applications of tests performed using the microELISA method and removes variations caused by uneven cell monolayers. It also allows quantification of NBT reduced by cells adherent to coverslips or in larger wells or Petri dishes, and can be used as a sensitive assay for macrophage activation by gamma-interferon.

Animals↗
PubMed1989

Stabilization of halophilic malate dehydrogenase.

Malate dehydrogenase from the extreme halophile, Halobacterium marismortui, is stable only in highly concentrated solutions of certain salts. Previous work has established that its physiological environment is saturated in KCl; it remains soluble is saturated NaCl or KCl solutions; also it unfolds in solutions containing less than 2.5 M-NaCl or -KCl, salt concentrations which are still relatively high. New data show that the structure of this enzyme can be stabilized in a range of high concentrations of Mg2+ or other "salting-in" ions, also with exceptional protein-solvent interactions. "Salting-in" ions, contrary to stabilizing protein structure, usually favour unfolding. These, and most other results concerning the structure, stability and solvent interactions of the protein cannot be understood in terms of the usual effects of salts on protein structure. In this paper, a novel stabilization model is proposed for halophilic malate dehydrogenase that can account for all observations so far. The model results from experiments on the protein in salt solutions chosen for their different effects on protein stability (potassium phosphate, a strongly "salting-out" agent, and MgCl2, which is "salting-in"), and previously published data from NaCl and KCl solutions (mildly "salting-out"). Enzymic activity and stability measurements were combined with neutron scattering, ultracentrifugation and quasi-elastic light-scattering experiments. The analysis showed that the structure of the protein in solution as well as the dominant stabilization mechanisms were different in different salt solutions in which this enzyme is active. Thus, in molar concentrations of phosphate ions, stabilization and hydration are similar to those of non-halophilic soluble proteins, in which the hydrophobic effect dominates. In high concentrations of KCl, NaCl or MgCl2, on the other hand, solution particles are formed in which the protein dimer interacts with large numbers of salt and water molecules (the mass of solvent molecules involved depends on the nature of the salt but it is approximately equivalent to the protein mass). It is proposed that, under these conditions, the hydrophobicity of the protein core is too weak to stabilize the folded structure and the main stabilization mechanism is the formation of co-operative hydrate bonds between the protein and hydrated salt ions. Model predictions are in agreement with all experimental results, such as the different numbers of solvent molecules found in the solution particles formed with different salts, the loss of the exceptional solvent interactions concomitant with unfolding at non-physiological salt concentrations, and the different temperature denaturation curves observed for different salt solutions.(ABSTRACT TRUNCATED AT 400 WORDS)

Buffers↗
PubMed1993

Wear of ceramic inlays, their enamel antagonists, and luting cements.

The wear of ceramic inlay materials and antagonist enamel cups was measured in vitro. Per group, six MOD inlays were adhesively cemented in extracted molars. Castable glass ceramic, pressed glass ceramic, and feldspathic porcelain were used as inlay materials. A microfilled and a fine hybrid composite served as luting agents. The restorations were exposed to an in vitro wear test that corresponds to approximately 5 years of clinical service. The wear in the occlusal contact area was quantified during and at the end of the test with a three-dimensional scanner. Final wear measurements on the inlays (mean +/- SD) ranged from 21.8 +/- 8.8 microns for pressed glass ceramic to 59.0 +/- 37.9 microns for castable glass ceramic. The mean wear of the enamel antagonists ranged from 74.6 +/- 32.9 microns for pressed glass ceramic to 153.2 +/- 61.5 microns for feldspathic porcelain. The wear of the luting composites at the end of the test ranged from 4.9 +/- 5.1 microns for microfilled to 12.3 +/- 6.3 microns for fine hybrid.

Aluminum Silicates↗
PubMed1993

Potassium nitrate-zinc oxide eugenol temporary cement for provisional crowns to diminish postpreparation tooth pain.

Pulpal injury commonly occurs with tooth preparation for complete fixed partial dentures. This can be documented by the substantial incidence of pain after tooth preparation. In this study, a 4% potassium nitrate-zinc oxide eugenol temporary cement was used to secure provisional crowns over recently prepared teeth and it significantly reduced the incidence and severity of pain after tooth preparation and impression taking.

Adult↗
PubMed1987

Corticosteroids and lung surfactant levels in adult male rats.

Following lung instillation in adult male rats of 3.4 mumol hexavalent chromium (K2Cr2O7) dissolved in 0.5 ml of 0.9% NaCl, increased levels of lung surfactant could be detected after 48 h. The blood serum concentration of corticosterone was elevated in these animals. Blood serum thyroxine and triiodothyronine showed an initial increase after lung instillation of hexavalent chromium followed by a decline. Metabolism of testosterone by the alveolar macrophages to 17 beta-hydroxy-5 alpha-androstane-3-one and 5 alpha-androstane-3 alpha, 17 beta-diol was reduced 6 and 12 h after the K2Cr2O7 instillation, which was also associated with damage of lung cell function and decreased uptake by the alveolar macrophages of Candida albicans particles. As early as 12 h after s.c. administration of 400 micrograms dexamethasone/100 g body wt, increased levels of lung surfactant could be measured. At this time the lungs showed no signs of cellular damage, and metabolism of testosterone as well as uptake of Candida albicans particles by the alveolar macrophages were normal. Lower s.c. doses of dexamethasone did not result in raising the levels of lung surfactant in 12 h. Within 12 h after s.c. administration of large doses of testosterone, dihydrotestosterone or dehydroepiandrosterone no measurable effects on the levels of lung surfactant could be measured. Since animals treated with dexamethasone (200 micrograms/100 g body wt) or long-acting synthetic ACTH (100 micrograms i.m. Synacthen Depot/100 g body wt) for 5 days after lung instillation of K2Cr2O7 had extremely high levels of lung surfactant, it is concluded that the corticosteroids in adult rats may help to create augmented surfactant levels following lung intoxication. This could proceed via stimulation of surfactant production and reduction of surfactant removal. Different aspects of lung surfactant metabolism are discussed.

Adrenal Cortex Hormones↗
PubMed1990

Pronounced and differential effects of ionic strength and pH on testosterone oxidation by membrane-bound and purified forms of rat liver microsomal cytochrome P-450.

The aim of this study was to determine the effects of ionic strength and pH on the different pathways of testosterone oxidation catalyzed by rat liver microsomes. The catalytic activity of cytochromes P-450a (IIA1), P-450b (IIB1), P-450h (IIC11) and P-450p (IIIA1) was measured in liver microsomes from mature male rats and phenobarbital-treated rats as testosterone 7 alpha-, 16 beta-, 2 alpha- and 6 beta-hydroxylase activity, respectively. An increase in the concentration of potassium phosphate (from 25 to 250 mM) caused a marked decrease in the catalytic activity of cytochromes P-450a (to 8%), P-450b (to 22%) and P-450h (to 23%), but caused a pronounced increase in the catalytic activity of cytochrome P-450p (up to 4.2-fold). These effects were attributed to changes in ionic strength, because similar but less pronounced effects were observed with Tris-HCl (which has approximately 1/3 the ionic strength of phosphate buffer at pH 7.4). Testosterone oxidation by microsomal cytochromes P-450a, P-450b, P-450h and P-450p was also differentially affected by pH (over the range 6.8-8.0). The pH optima ranged from 7.1 (for P-450a and P-450h) to 8.0 (for P-450p), with an intermediate value of 7.4 for cytochrome P-450b. Increasing the pH from 6.8 to 8.0 unexpectedly altered the relative amounts of the 3 major metabolites produced by cytochrome P-450h. The decline in testosterone oxidation by cytochromes P-450a, P-450b and P-450h that accompanied an increase in ionic strength or pH could be duplicated in reconstitution systems containing purified P-450a, P-450b or P-450h, equimolar amounts of NADPH-cytochrome P-450 reductase and optimal amounts of dilauroylphosphatidylcholine. This result indicated that the decline in testosterone oxidation by cytochromes P-450a, P-450b and P-450h was a direct effect of ionic strength and pH on these enzymes, rather than a secondary effect related to the increase in testosterone oxidation by cytochrome P-450p. Similar studies with purified cytochrome P-450p were complicated by the atypical conditions needed to reconstitute this enzyme. However, studies on the conversion of digitoxin to digitoxigenin bisdigitoxoside by liver microsomes, which is catalyzed specifically by cytochrome P-450p, provided indirect evidence that the increase in catalytic activity of cytochrome P-450p was also a direct effect of ionic strength and pH on this enzyme.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Effects of synthetic blood and crystalloid cardioplegic solutions on coronary endothelium: an experimental scanning electron microscope study.

In an experimental study the effects of Fluosol DA (added with potassium chloride) on the vascular interface and endothelial cells were compared to those of crystalloid potassium cardioplegic solution using scanning electron microscope. Twenty rabbits (10 in each group) were sacrificed, the hearts with ascending aorta were immediately excised, and cold oxygenated solution was infused via a cannula inserted into the cross-clamped aorta. The hearts were left immersed in the perfusion medium for 2 hr. In the Fluosol DA group endothelial cover and endothelial cells were normal or minimal changes were seen in seven cases. Occasional breaking of intercellular attachments, small areas of denuded flow surface, and disappearance of microvilli were seen in three cases. In the crystalloid potassium cardioplegic group 7 of the 10 cases showed moderate or severe damage with large areas of denuded flow surface. The present experimental protocol represented an extreme situation where no collateral coronary blood was present. The coronary endothelial damage was obvious after the crystalloid potassium cardioplegic solution. Similar damage was not found following Fluosol DA infusion.

Animals↗
PubMed1988

Decreased postoperative myocardial fatty acid oxidation.

Myocardial substrate preferences following cardioplegic arrest for coronary bypass surgery have not been established. Fatty acids are believed to be the major fuel source for aerobic metabolism. Following cardioplegic arrest arterial fatty acid levels are elevated and myocardial fatty acid accumulation without oxidation may contribute to reperfusion injury. Perioperative fatty acid metabolism was evaluated in 18 patients undergoing elective coronary bypass surgery who were randomized to receive either blood (n = 11) or crystalloid (n = 7) cardioplegia. Palmitate labeled with 14carbon was infused perioperatively and arterial and coronary sinus blood samples were obtained to calculate myocardial fatty acid extraction and oxidation before and after cardioplegic arrest. Lactate and glycerol were released from the heart during both blood and crystalloid cardioplegia, suggesting ischemic glycolysis and lipolysis. Myocardial oxygen consumption was depressed and the myocardial consumptions of lactate, glucose, and fatty acids were minimal during the first 60 min after aortic clamp removal in both groups despite high arterial concentrations. Fatty acid oxidation was minimal after blood cardioplegia and was not found after crystalloid cardioplegia. Fatty acids were extracted by the heart, but were not aerobically metabolized following cardioplegic arrest. Myocardial fatty acid accumulation without oxidation may have been deleterious. The inability of the heart to oxidize exogenous fatty acids may reflect altered myocardial exogenous substrate preferences during reperfusion following coronary bypass surgery.

Cardioplegic Solutions↗
PubMed1986

3H-5-hydroxytryptamine accumulation by rat brain synaptic vesicles in a membrane-impermeant medium, and selective reduction by 5,7-dihydroxytryptamine.

In order to examine possible selectivity of amine uptake by synaptic vesicles, the ATP-stimulated accumulation of 3H-5-hydroxytryptamine (5HT) by synaptic vesicles from rat whole brain was examined in a medium comprised largely of membrane-impermeant anions (d-tartrate). Such media have previously been shown to stabilize vesicular accumulation of several neurotransmitters. Accumulation of 3H-5HT did not occur in tartrate medium alone, but was increased biphasically with increasing concentrations of both potassium phosphate and potassium bicarbonate. At optimal concentrations of each anion (10 mM), stable accumulation of 3H-5HT was observed at 37 degrees (26.1 +/- 1.2 pmol/mg protein; Km 6 X 10(-7) M), which was reduced by greater than 95% in the absence of K2ATP, at 4 degrees C, in the presence of 10(-6) M reserpine, or in the presence of the proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Uptake was significantly antagonized by millimolar concentrations of Na+, Mg++ or Cl-, but was unaffected by ouabain (10(-5) M). Pretreatment of animals with 5,7-dihydroxytryptamine (5,7-DHT) (200 micrograms, intraventricular) 10 days prior to sacrifice reduced endogenous 5HT levels by 70%, while levels of endogenous norepinephrine (NE) and dopamine (DA) were unaffected. Accumulation of 3H-5HT, examined in the presence of 10(-6) M NE to block 3H-5HT accumulation by vesicles from noradrenergic nerve endings, was reduced by 40% in vesicles from treated animals. Vesicular accumulation of 3H-(-)-NE and 3H-DA was unaffected by 5,7-DHT treatment. The data suggest the possibility of preferential accumulation of 3H-5HT by vesicles arising from serotonergic nerve endings.

5,7-Dihydroxytryptamine↗