PubMed Health⌕ Search

Biomedical subjects

P Spencer

Publications and source records attributed to P Spencer.

At least 19 recordsLinked to original sources
PubMed1992

Effects of 2(3)-tert-butyl-4-hydroxyanisole (BHA) on in situ mitochondria of Trypanosoma cruzi.

Results obtained with in situ mitochondria of Trypanosoma cruzi showed that this protozoon had only two energy coupling sites, sites II and III that correspond to higher eukaryote mitochondria. Rotenone did not inhibit the oxygen uptake of the parasite. These results suggest that the NADH-ubiquinone segment of the respiratory chain has no activity. Studies with in situ mitochondria confirmed that BHA, an antioxidant food additive, blocks the mitochondrial electron transport chain at the succinate-cytochrome b segment being the molecular basis of this trypanocidal action.

Adenosine Diphosphate↗
PubMed1992

Chemical characterization of the dentin/adhesive interface by Fourier transform infrared photoacoustic spectroscopy.

Irreversible bonding of composite materials to tooth structure depends on chemical as well as mechanical adhesion. The proposed bonding mechanism for several commercial dental adhesives is chemical adhesion to the dentin surface. The purpose of this in vitro investigation was to characterize the chemical nature of the surface interaction between dentin and two commercial adhesives by use of Fourier transform infrared photoacoustic spectroscopy (FTIR/PAS). The occlusal thirds of the crowns of freshly extracted, non-carious, unerupted human molars were sectioned perpendicular to the long axis. Dentin disks, 6 mm x 2 mm, were prepared from these sectioned teeth. The exposed dentin surface was treated with either Scotchbond 2, a BIS-GMA resin, or Dentin-Adhesit, a polyurethane resin. All spectra were recorded from 4000 to 400 cm-1 by use of an Analect RFX-65 FTIR spectrometer equipped with an MTEC Photoacoustics Model 200 photoacoustic cell. An initial spectrum of the dentin surface was collected. This surface was primed according to manufacturer's instructions and spectra recorded of the primed surface plus one to three layers of adhesive. By comparison of these spectra, it was possible for us to record changes in the phosphate and amide I and II bands due to surface interactions between the adhesive and the dentin. Although early results do not indicate covalent bonding between the dentin and these adhesives, this technique presents several advantages for spectroscopic evaluation of the dentin/adhesive interface.

Acrylic Resins↗
PubMed1992

Effects of hydroquinones on intact Trypanosoma cruzi epimastigotes.

1. Hydroquinones inhibited the culture growth of Trypanosoma cruzi epimastigotes at concentrations lower than 1 mM. 2. Hydroquinones inhibited the oxygen consumption on the intact Trypanosoma cruzi cells. I50 values for hydroquinone, terbutylhydroquinone and 2,5-di-t-butylhydroquinone were 24.87 mM, 0.88 mM and 0.26 mM, respectively. t-Butylhydroquinone and 2,5-di-t-butylhydroquinone had a Michaelian type kinetic inhibition; hydroquinone also showed a Michaelian type kinetic inhibition at low concentrations but at higher concentrations it showed a positive cooperativity. 3. These hydroquinones changed the NAD(P) redox-state to a more reduced state and that of cytochrome b to a more oxidized state. The magnitude of the redox-state change was dependent of the hydrophobicity of the derivates. 4. These results suggest that the growth and oxygen uptake inhibition by the hydroquinones is due to a blockage of the mitochondrial electron transport chain before cytochrome b.

Animals↗
PubMed1992

Mesenteric angioplasty for chronic intestinal ischaemia.

Mesenteric angina is a difficult diagnosis and surgical treatment carries a significant morbidity and mortality. In patients with stenotic mesenteric vascular disease angioplasty offers an alternative method of treatment. In six patients who underwent mesenteric angioplasty relief of symptoms was achieved in five. Recurrence of symptoms associated with recurrent stenosis occurred in two patients and was remedied by re-dilation in one. Mesenteric angioplasty is a safe alternative to surgical revascularisation for mesenteric stenosis causing chronic intestinal ischaemia.

Aged↗
PubMed1992

Interactions between parents and pediatric primary care physicians about children's mental health.

Interaction patterns between parents and pediatricians were examined during 1,378 well-child visits to four public and private pediatric clinics. During 327 visits, parents listed at least one psychosocial concern related to their child's mental health. At 37 percent of these visits, parents said they did not wish to discuss the concern with the physician. Physicians failed to address concerns during approximately 35 percent of visits at which parents were willing to discuss them. Successful parent-physician interactions were three times more frequent in private practices than in a public clinic; they were more likely when fewer concerns were stated and less likely when behavior problems were the concern. Parents concerned about the parent-infant relationship were four times more likely to be referred to outside mental health services, although these cases were relatively rare. Older children and families receiving Medicaid were also more likely to be referred to such services.

Child↗
PubMed1992

The effects of the Nd:YAG laser on in vitro fibroblast attachment to endotoxin-treated root surfaces.

The purpose of this study was to evaluate the effects of the Nd:YAG laser on in vitro fibroblast attachment to endotoxin-treated root surfaces and to describe any laser-induced cementum surface alterations. Thirty 4 mm x 4 mm cementum segments were obtained from unerupted third molars. The treatment groups were as follows: 1) control, healthy root segment; 2) non-lased, endotoxin treated; and 3) lased, endotoxin treated. The endotoxin treated roots were soaked in E. coli 055:B5 lipopolysaccharide (556 EU/ml) for 72 hours. The lased, endotoxin-treated root segments were treated with a Nd:YAG laser using a 320 microns contact optic fiber handpiece with an energy setting of 80 mJ at 10 pulses per second for one minute. The root segments were subsequently placed in fibroblast culture dishes for 40 hours and then prepared for scanning electron microscopy (SEM) observation. SEM examination revealed two different types of attachment: flat and round. Flat cells represented firmly attached cells due to well-defined points of attachment and numerous lamellapodia. Round cells possessed few attachment processes and were, therefore, considered poorly attached. The lased, endotoxin-treated root segments had significantly decreased numbers of flat fibroblasts versus the control and non-lased, endotoxin-treated root segments. The absence of flat fibroblasts in the laser treated root segments was a consistent finding. The non-lased, endotoxin-treated root segments had significantly increased numbers of round fibroblasts versus the control and lased, endotoxin treated groups. The lased root segments exhibited surface alterations which included charring, crater formation, cementum meltdown, and tracking.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Silicates↗
PubMed1992

Chemical characterization of lased root surfaces using Fourier transform infrared photoacoustic spectroscopy.

Recently lasers have been recommended as an alternative or adjunctive therapy in the control and treatment of periodontally diseased root surfaces. The purpose of this in vitro investigation was to characterize the chemical structure of lased root surfaces using Fourier transform infrared photoacoustic spectroscopy (FTIR/PAS). Cementum samples, 6 mm x 2 mm, were cut from the root surface of extracted non-carious, unerupted human molars. The experimental samples were lased with a Nd:YAG laser at an average energy of 80 mJ at 10 pulses per second. Total lasing time ranged from 1 minute 45 seconds to 4 minutes. A non-lased cementum sample served as the control. All spectra were recorded from 4000 to 400 cm-1 using the photoacoustic cell attachment on an Analect RFX-65 FTIR Spectrometer. Photoacoustic FTIR spectra of lased cementum samples showed a decrease in the protein/mineral ratio in comparison to the control. Breakdown of protein at the root surface potentially contributed to an ammonium band at 2010 cm-1. The decreased protein/mineral ratio and the potential surface contamination with protein by-products, may ultimately affect cell reattachment at the cementum surface.

Acoustics↗
PubMed1992

Trends in dental treatment rendered under general anesthesia, 1978 to 1990.

While it is generally accepted that the prevalence of dental caries is decreasing, many institutions report an increase in the demand for dental rehabilitation under general anesthesia. This paper compares the characteristics of patients and types of dental treatment delivered under general anesthesia at the same hospital during 1978-1980 and 1988-1990. Patient records for children, who received dental care under general anesthesia during the two time periods examined were reviewed. Demographic data as well as data pertaining to types of dental treatment performed were collected from each patient record. Demographic characteristics were analyzed with a chi square analysis, and results regarding the types of dental treatment were analyzed using a Students t-test. Results were considered significant at p less than 0.05. There were no statistically significant differences in gender or ethnicity of the patients treated during 1978-1980 compared to 1988-1990. There were statistically significantly more patients treated in the 4-6 age group during 1988-1990 than during 1978-1980. There were no statistically significant differences in the number of dental procedures completed per patient during 1978-1980 compared to 1988-1990 in any procedure category except for dental sealants. This study indicates that the majority of pediatric dental patients being treated under general anesthesia at this hospital facility, still require an extensive amount of restorative dental care. Although most children can be successfully treated in the dental office, there is a group of pediatric patients, who require dental treatment in the hospital, under general anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Dental↗
PubMed1992

The dentinal surface: its influence on dentinal adhesion. 2.

The first paper in this series presented a categorization of dentinal adhesive systems that was organized roughly according to chronology, chemistry, and shear bond strength values. Category I dentinal adhesives demonstrate the lowest shear bond strength values, approximately 5 to 7 MPa. Category II dentinal adhesives, including experimental ferric and aluminum oxalate pretreatments and two commercial products, demonstrate shear bond strength values between 8 and 14 MPa. This second category of dentinal adhesives is the subject of this paper. An attempt is made to draw a parallel between the penetrative ability of the adhesive (the wettability of the dentinal substrate) and the efficacy of the adhesive bond as determined by shear bond strength values. Category III dentinal adhesives will be discussed in another paper.

Adhesives↗
PubMed1991

The identification of a structurally important cysteine residue in the glycerol dehydrogenase from Bacillus stearothermophilus.

Evidence is presented to demonstrate that the Zn2+ metallo-enzyme glycerol dehydrogenase from the thermophile Bacillus stearothermophilus has one cysteine residue per subunit which is only available for reaction with thiol reagents in the metal-depleted form of the enzyme. Modification of the metal-depleted enzyme by methyl methanethiosulphonate prevents the reactivation of the enzyme by Zn2+ ions and induces dissociation of the oligomer into subunits. The rate of reaction of the cysteine residue with the thiol reagent DTNB is limited by a factor other than reagent concentration and it is proposed that the reagent only reacts with the cysteine residue in dissociated monomers. The enzyme has been labelled at the single cysteine residue by radioactive iodo[2-3H]acetic acid. Two radiolabelled peptides have been isolated and sequenced; one peptide is a component of the other. Spectroscopic evidence suggests that the cysteine residue is not involved in ligation of the essential metal ion. Chemical modification studies using the reagent diethylpyrocarbonate have suggested that two histidines are involved in the ligation of the metal.

Chemical Phenomena↗
PubMed1991

The dentinal surface: its influence on dentinal adhesion. Part I.

Three categories of dentinal adhesive are proposed: category I includes adhesives with shear bond strength values between 5 and 7 MPa; category II includes dentinal adhesives with shear bond strengths between 8 and 14 MPa; and category III includes adhesives with shear bond strength values up to 20 MPa. In part I of this article, photomicrographs of the dentinal smear layer and three category I first-generation dentin-adhesive interfaces are presented. The photomicrographs show that the wetting and penetration of the first-generation dentinal adhesives were not adequate to produce high shear bond strengths. When the category I adhesives were tested for shear bond strength, failures occurred at the interface or in the resin adhesive. Future articles will explain wetting and adhesive performance of category II and III adhesives.

Acrylic Resins↗
PubMed1991

Splenic artery ligation for splenic salvage: clinical experience and immune function.

Documentation of overwhelming post-splenectomy sepsis, characterized by infection from encapsulated organisms, has led to development of surgical techniques for preservation of the injured spleen to maintain splenic clearance of encapsulated, opsonized organisms from the circulation. In this study splenic artery ligation (SAL) was performed as an adjunct to successful splenorrhaphy in 20 adults suffering blunt splenic injury. There were no deaths and no reoperations. Twenty units of blood were transfused in ten patients. Splenic removal of blood-borne opsonized particles was measured as the clearance of anti-Rh-antibody-coated 51Cr-radiolabeled autologous red blood cells from the circulation in five SAL patients and nine normal volunteers. The clearance of opsonized red cells 120 minutes after injection was not different (40 +/- 7% of injected dose in controls, 40 +/- 4% in SAL patients). These results demonstrate that SAL can safely be applied as an adjunct to splenorrhaphy and that SAL does not diminish splenic clearance of opsonized particles from the circulation.

Adolescent↗
PubMed1990

Studies on the interactions of glycerol dehydrogenase from Bacillus stearothermophilus with Zn2+ ions and NADH.

The interactions of the essential divalent cation, Zn2+, with the binary complex formed between glycerol dehydrogenase (glycerol:NAD+ 2-oxidoreductase, EC 1.1.1.6) and its coenzyme NADH have been examined by fluorescence spectroscopy. Both the metallo and non-metallo form of the enzyme bind the coenzyme NADH. The addition of Zn2+ ions to a solution of the binary complex formed between metal-depleted enzyme and NADH results in a rapid increase in fluorescence emission at 430 nm. This has been used to determine the on rate for Zn2+ to the enzyme/binary complex. A dissociation constant of 3.02 +/- 0.25.10(-9) M for the equilibrium between Zn2+ ions and the enzyme has been determined.

Geobacillus stearothermophilus↗
PubMed1990

Identification of a reversible structural transition in the metal-depleted glycerol dehydrogenase from Bacillus stearothermophilus.

Evidence is presented to demonstrate that the Zn2+ -depleted, inactive form of the glycerol dehydrogenase from Bacillus stearothermophilus exists in one of two possible conformations in equilibrium, the position of which is temperature sensitive. The conformation of the metal-depleted enzyme favoured by higher temperatures (20-40 degrees C) is able to bind Zn2+ and regain catalytic activity, whereas that favoured at lower temperatures (0-10 degrees C) is unable to bind metal ions and is thus inactive. This equilibrium is also pH dependent with a pK of 6.6. At pH 6.0, the equilibrium lies in favour of the form of the enzyme able to bind metal ions and exhibit activity.

Geobacillus stearothermophilus↗
PubMed1990

Plant-derived neurotoxic amino acids (beta-N-oxalylamino-L-alanine and beta-N-methylamino-L-alanine): effects on central monoamine neurons.

In the present study the subacute effects of beta-N-oxalylamino-L-alanine (BOAA) and beta-N-methylamino-L-alanine (BMAA) on CNS monoamine neurons in rats were investigated following intracisternal injections or local intracerebral administration into substantia nigra. In vitro effects of BOAA and BMAA on high-affinity synaptosomal uptake of dopamine (DA), noradrenaline (NA), and serotonin (5-HT) were also examined. Intracisternal administration of BMAA decreased NA levels in hypothalamus, whereas no effects were seen on DA or 5-HT levels. Following intranigral injections of BOAA, NA levels tended to decrease in several regions, whereas the DA levels and the levels of DA metabolites were unaffected in all regions analyzed. Loss of tyrosine hydroxylase (TH) immunoreactivity in the intranigral injection sites and the presence of TH-immunoreactive pyknotic neurons near the borders of the injection sites were observed following both BOAA and BMAA treatments. Furthermore, substance P-immunoreactive terminals in substantia nigra pars reticulata were also found to have disappeared within the lesioned area following either BOAA or BMAA injections. Incubations with both BOAA and BMAA (10(-5) M) reduced high-affinity [3H]NA uptake in cortical synaptosomes to 69% and 41% of controls, respectively, whereas the striatal high-affinity [3H]DA uptake and the cortical high-affinity [3H]5-HT uptake were unaffected by BOAA or BMAA. The results demonstrate that both BOAA and BMAA can affect central monoamine neurons, although the potency and specificity of these substances on monoamine neurons when administered acutely into cerebral tissue or liquor cerebri seem to be low. However, the in vitro studies indicate selective effects of both compounds on NA neurons in synaptosomal preparations.

Alanine↗
PubMed1990

[Nontraumatic deaths associated with a natural catastrophe. The experience of the earthquake in Chile 1985].

We analyzed causes of death before and after the March 1985 earthquake in Valparaíso, Chile. Causes of death were obtained from death certificates. Apart from death directly due to trauma during the earthquake, a significant increase was observed in deaths due to accidents (+51), cardiovascular disease (+38), malnutrition (+13) and psychiatric disorders (+13). Retired males over age 65 were most affected.

Adolescent↗
PubMed1989

Isolation and characterisation of the glycerol dehydrogenase from Bacillus stearothermophilus.

A protocol for the rapid purification of the glycerol dehydrogenase (glycerol: NAD+ 2-oxidoreductase, EC 1.1.1.6) from the thermophile Bacillus stearothermophilus has been developed using a combination of chromatographic techniques including affinity chromatography on a Sepharose-immobilised triazine dye (Procion red, HE3B, ICI). Substrate specificity has been examined and Km values determined. The protein has been shown to have an oligomeric Mr of approx. 180,000 and consists of four identical subunits of Mr 42,000. Exposure to chelating agents (e.g., EDTA) leads to total loss of activity; the EDTA-inactivated enzyme can be reactivated by Zn2+ and requires 1 mol equivalent of zinc per subunit for full catalytic activity. Other divalent cations such as Cd2+ and Co2+ will reactivate the apo-enzyme but yields an enzyme of lower specific activity. The enzyme binds 1 equivalent of NADH per subunit and during catalysis transfers the 4-pro-R hydride from the nicotinamide ring of the reduced-coenzyme to the substrate. Glycerol increases the dissociation constant for the interaction between NADH and Zn-metallo-glycerol dehydrogenase (ZnGDH) but has no effect on the equilibrium between NADH and metal-depleted enzyme.

Amino Acids↗