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Biomedical subjects

C A Smith

Publications and source records attributed to C A Smith.

At least 343 records · Page 19Linked to original sources
PubMed1993

Effects of memory from vagal feedback on short-term potentiation of ventilation in conscious dogs.

1. We assessed short-term potentiation of ventilation in response to brief systemic normocapnic hypoxaemia in conscious dogs. Four recumbent dogs were exposed to Pa, O2 35-55 mmHg with Pa, CO2 maintained normocapnic for forty to fifty seconds and then abruptly returned to normoxia. Minute ventilation (VI) increased 4- to 5-fold during hypoxia due to both increased tidal volume (VT) and frequency (f). Several trials of hypoxic exposure with normoxic restoration were conducted with animals intact and following bilateral cold blockade of the cervical vagus nerves sufficient to block completely the Hering-Breuer reflex. 2. In the vagally intact dog, when normoxia was restored immediately following normocapnic hypoxia (PET, O2 = 40 Torr), expiratory time (TE) was prolonged to 190 +/- 68% of control (mean +/- S.E.M., range 53-350%) on the second or third breath and then returned slowly to control values on subsequent breaths. The prolongation of TE following removal of the hypoxic stimulus was positively correlated with the magnitude of the peak VT reached during hypoxic exposure. However, VT and VI remained significantly greater than control over a twenty second or four-breath period following hypoxia. 3. In the vagally blocked dog, no prolongation of TE was observed following isocapnic hypoxia; nor was TE following hypoxia correlated with the magnitude of the VT during hypoxia. The time constants of decay of VI, VT and f back to control, following hypoxia averaged 16, 19 and 9 s, respectively. 4. We conclude that short-term potentiation of ventilatory output following peripheral chemoreceptor hypoxic stimulation does exist in the awake dog, but the stimulatory after-effect is masked and TE is prolonged by a 'memory' of inhibitory vagal feedback. The magnitude of this inhibitory after-effect on TE prolongation increases in proportion to the increase in tidal volume achieved during the hypoxaemia. 5. This inhibitory effect of vagal memory may contribute to instability of breathing pattern and apnoea following transient disturbances in ventilatory output.

Animals↗
PubMed1993

Enterobacter taylorae, a new opportunistic pathogen: report of four cases.

Severe nosocomial infections due to Enterobacter taylorae (formerly known as CDC Enteric Group 19) are described in four patients. Unlike most members of the Enterobacter genus, the isolates were not susceptible to penicillins or cephalosporins. Restriction endonuclease analysis of E. taylorae DNA obtained from three patients identified two distinct strains. One strain was found in two patients, suggesting a common source which we were not able to identify. We postulate that in patients harboring E. taylorae, the combination of cephalosporin therapy and instrumentation enables this organism to become an opportunistic pathogen.

Aged↗
PubMed1993

ICP4, the major transcriptional regulatory protein of herpes simplex virus type 1, forms a tripartite complex with TATA-binding protein and TFIIB.

The ICP4 protein of herpes simplex virus can either increase or decrease the rate of transcription mediated by RNA polymerase II, depending on the target promoter. The interplay of DNA-protein and protein-protein contacts determining ICP4 function has yet to be characterized, and consequently the molecular mechanism by which the protein acts remains unclear. ICP4 can transactivate minimal promoters containing only TATA homologies, and therefore it is reasonable to hypothesize that ICP4 works by influencing the TATA-dependent assembly of general transcription factors via specific protein-protein interactions. This study directly addresses this hypothesis by determining whether ICP4 affects the assembly of general transcription factors on templates bearing a TATA box and an ICP4-binding site. Using gel retardation and footprinting assays, we found that ICP4 forms a tripartite complex with TFIIB and either the TATA-binding protein (TBP) or TFIID. The formation of this complex was not the result of simple tripartite occupancy of the DNA but the consequence of protein-protein interactions. In the presence of all three proteins, the affinity of ICP4 and TBP for their respective binding sites was substantially increased. Using mutant derivatives of ICP4 and defective versions of promoters, we also demonstrated that the ability of ICP4 to regulate gene expression correlated with its ability to form a tripartite complex with TFIIB and TBP in vitro.

Animals↗
PubMed1993

Effects of rapid-eye-movement sleep on the apneic threshold in dogs.

We determined whether the apneic threshold after active hyperventilation was different in rapid-eye-movement (REM) vs. non-REM (NREM) sleep. Sleeping dogs were repeatedly exposed to 35-45 s of hypoxia of varying severity (end-tidal PO2 40-60 Torr) that was abruptly terminated with 100% O2. Changes in breathing pattern after brief hypoxia were compared with those after a normoxia-to-hyperoxia transition, i.e., control conditions. In NREM sleep, hypoxic hyperventilation was consistently followed by central apnea, the duration of which was linearly related to the corresponding hypocapnia and/or increase in tidal volume (VT) during hypoxia. After hypoxia, expiratory duration averaged 3.5 x control value at -5-Torr change in end-tidal PCO2 and twofold increase in VT; mean expiratory duration was 5 x control value at -10-Torr change in end-tidal PCO2 and fourfold increase in VT. In REM sleep, central apnea of varying duration did occur on occasion after brief hypoxic hyperventilation, but there was no systematic relationship with magnitude of hypocapnia or increase in VT. Breathing pattern during or after hypoxia in REM was not related to temporal changes in either eye movement density or electroencephalogram frequency. Thus, in contrast to NREM sleep, in REM sleep ("phasic" or "tonic") a posthyperventilation apneic threshold was not present. We attribute this effect of REM to 1) a reduced VT response to hypoxia that would minimize inhibitory "memory" effect from lung stretch and 2) attenuated inhibitory response to any given magnitude of hypocapnia or increased VT. Active hyperventilation-induced apneic threshold may be "masked" by actions of nonchemoreceptor and nonmechanoreceptor inputs affecting respiratory motor output in REM sleep. These data are consistent with the relative absence of central apnea and periodic breathing in humans in REM sleep.

Animals↗
PubMed1993

Tissue-specific regulation of shell gland calbindin D28K biosynthesis by estradiol in precociously matured, vitamin D-depleted chicks.

Provision of Ca2+ for egg shell calcification in the avian uterus [egg shell gland (ESG)] derives mostly from vitamin D-dependent intestinal Ca2+ absorption from the diet. Ca2+ absorption is strongly linked to the intestinal vitamin D-dependent calbindin D28K (D28K) concentration. The laying hen ESG also contains D28K, and again, Ca2+ transport into the shell appeared to be linked to the ESG D28K concentration. However, evidence is now presented that ESG D28K synthesis may be estradiol (E2) dependent and vitamin D independent under certain conditions. One-day-old female chicks fed a vitamin D-free diet for as long as 6 weeks and then repeatedly injected im with E2 for up to 3 more weeks developed frank rickets, but possessed precociously matured reproductive tracts. While the tiny presumptive ESGs of nonestrogenized vitamin D-depleted chicks were devoid of D28K, the highly developed ESG, including the isthmus, of estrogenized chicks contained D28K. The ESGs of nonestrogenized, vitamin D-replete chicks also exhibited no development or detectable D28K. Regardless of whether vitamin D depleted or replete, estrogenized chick ESG contained similar D28K and D28K mRNA concentrations. Immunohistochemical techniques showed that the endometrial cellular localization of both D28K and Ca(2+)-ATPase (Ca2+ pump) in estrogenized chicks was similar to that in mature laying hens. There was no trace of D28K, nor was there any stimulation of Ca2+ absorption, in duodenum of vitamin D-free, immature chicks regardless of E2 treatment. As expected, both D28K and D28K mRNA were present in vitamin D-replete chick duodenum. We conclude that in E2-treated chicks, ESG D28K gene expression may be vitamin D independent and E2 dependent. This is the first clear demonstration of hormone-dependent tissue-specific D28K gene expression in the chick.

Animals↗
PubMed1993

Consumption of fruits and vegetables in Missouri.

High consumption of fruits and vegetables has been linked with a reduced risk of several important chronic diseases. The authors utilized telephone survey techniques to assess the level of fruit and vegetable consumption among adult Missouri residents. Only 28% of respondents reported consumption of five servings of fruits and vegetables per day. Older females had the highest rate of consuming five servings per day, while young males had the lowest rate. These findings, in conjunction with national data, show the need for increasing emphasis on the "5 A Day" campaign.

Adolescent↗
PubMed1993

Variations in three cardiovascular disease risk factors in Missouri, 1986-1992.

In 1991, cardiovascular disease claimed the lives of over 22,000 Missourians. Recent studies show that much of this mortality can be eliminated through risk factor reduction and early detection. This article examines the regional and demographic differences in three major cardiovascular disease risk factors and outlines some steps that physicians and other health care providers can take to reduce their prevalence.

Adult↗
PubMed1993

Patterns of obesity in Missouri.

Obesity is a major preventable health problem in Missouri and in the nation. Using survey data, we examined the prevalence of obesity in population subgroups and the overall trend. Prevalence of obesity was higher among blacks, middle-aged persons, and persons with less education or lower family income. Without additional attention, Missouri is unlikely to achieve the year 2000 objective of < or = 20% prevalence of obesity.

Adult↗
PubMed1992

Crosstalk between plasmid vegetative replication and conjugative transfer: repression of the trfA operon by trbA of broad host range plasmid RK2.

Previous deletion and complementation analysis has indicated that the region between trfA and kilBI (trbB) encodes trans-acting factor, designated trbA, required for conjugative transfer of broad host range plasmid RK2. In analysing the nucleotide sequence of this region we have discovered a gene encoding a 12 kDa polypeptide. The predicted amino acid sequence of this protein shows similarity at its C-terminal to KorA from the central control operon of RK2 and at its N-terminal to immunity repressor protein from phage phi 105 of Bacillus subtilis as well as the Sin protein of B. subtilis which regulates alternate developmental processes including sporulation, motility and competence. We show that TrbA represses transcription of both trfA (vegetative replication) and kilBI (trbB) (required for conjugative transfer and whose product has similarity to ComG, required for competence of B. subtilis) and may help to coordinate expression of both sets of functions. This region has similarities to some temperate bacteriophage immunity regions in modulating divergent transcription required for alternative means of propagation.

Amino Acid Sequence↗
PubMed1992

Use of soluble recombinant TNF receptor to improve detection of TNF secretion in cultures of tumor infiltrating lymphocytes.

The accurate quantitation of picogram amounts of TNF is possible by ELISA and is useful in many areas of biomedical research, including studies of TNF release in vitro by stimulated lymphocytes and macrophages, and of serum levels in patients with cancer and sepsis. However, we show in this report that the detection of recombinant TNF standards by ELISA falls over time with incubation at 37 degrees C, and is further decreased when incubated with tumor infiltrating lymphocytes (TIL), making accurate quantitation difficult. We demonstrate that the soluble dimeric form of the TNF receptor can prevent this decrease, both in the presence and absence of TIL. In contrast, the soluble monomeric TNF receptor was much less effective in preventing this decrease. In addition, the dimeric but not the monomeric TNF receptor was found to inhibit bioactivity of TNF as measured by L929 cytotoxicity. The dimeric TNF receptor does not interfere with the detection of recombinant TNF standards by ELISA, and entirely stabilizes TNF levels incubated over 48 h at 37 degrees C in the presence and absence of TIL. This protection is specific, and the TNF receptor does not stabilize interferon-gamma. The dimeric form of the soluble TNF receptor has proven useful in detecting TNF released by TIL transduced with the TNF cDNA that are currently being used in studies of the gene therapy of cancer with TIL. The dimeric TNF receptor may also prove useful in the accurate quantitation of TNF released by stimulated lymphocytes and macrophages in vitro, and in the quantitation of serum TNF levels in patients.

Biological Assay↗
PubMed1992

Debrisoquine hydroxylase gene polymorphism and susceptibility to Parkinson's disease.

The pathogenesis of Parkinson's disease may be influenced by genetic and environmental factors. Cytochrome P450 mono-oxygenases help to protect against toxic environmental compounds and individual variations in cytochrome P450 expression might, therefore, influence susceptibility to environmentally linked diseases. The frequency of mutant CYP2D6 alleles was studied in 229 patients with Parkinson's disease and 720 controls. Individuals with a metabolic defect in the cytochrome P450 CYP2D6-debrisoquine hydroxylase gene with the poor metaboliser phenotype had a 2.54-fold (95% Cl 1.51-4.28) increased risk of Parkinson's disease. Determination of CYP2D6 phenotype and genotype may help to identify those at greatest risk of Parkinson's disease and may also help to identify the environmental or metabolic agents involved in the pathogenesis of this disease.

Cytochrome P-450 CYP2D6↗
PubMed1992

Anion binding by human lactoferrin: results from crystallographic and physicochemical studies.

The anion-binding properties of lactoferrin (Lf), with Fe3+ or Cu2+ as the associated metal ion, have been investigated by physicochemical and crystallographic techniques. These highlight differences between the two sites and in the anion-binding behavior when different metals are bound. Carbonate, oxalate, and hybrid carbonate-oxalate complexes have been prepared and their characteristic electronic and EPR spectra recorded. Oxalate can displace carbonate from either one or both anion sites of Cu2(CO3)2Lf, depending on the oxalate concentration, but no such displacement occurs for Fe2(CO3)2Lf. Addition of oxalate and the appropriate metal ion to apoLf under carbonate-free conditions gives dioxalate complexes with both Fe3+ and Cu2+, except when traces of EDTA remain associated with the protein, when hybrid complexes M2(CO3)(C2O4)Lf can result. The anion sites in the crystal structures of Fe2(CO3)2Lf, Cu2-(CO3)2Lf, and Cu2(CO3)(C2O4)Lf, refined at 2.2, 2.1, and 2.2 A, respectively, have been compared. In every case, the anion is hydrogen bonded to the N-terminus of helix 5, an associated arginine side chain, and a nearby threonine side chain. The carbonate ion binds in bidentate fashion to the metal, except in the N-lobe site of dicupric lactoferrin, where it is monodentate; the difference arises from slight movement of the metal ion. The hybrid complex shows that the oxalate ion binds preferentially in the C-lobe site, in 1,2-bidentate mode, but with the displacement of several nearby side chains. These observations lead to a generalized model for synergistic anion binding by transferrins.

Binding, Competitive↗
PubMed1992

Metal substitution in transferrins: the crystal structure of human copper-lactoferrin at 2.1-A resolution.

The structural consequences of binding a metal other than iron to a transferrin have been examined by crystallographic analysis of human copper-lactoferrin, Cu2Lf. X-ray diffraction data were collected from crystals of Cu2Lf, using a diffractometer, to 2.6-A resolution, and oscillation photography on a synchrotron source, to 2.1-A resolution. The structure was refined crystallographically, by restrained least-squares methods, starting with a model based on the isomorphous diferric structure from which the ligands, metal ions, anions, and solvent molecules had been deleted. The final model, comprising 5321 protein atoms (691 residues), 2 Cu2+ ions, 2 (bi)carbonate ions, and 308 solvent molecules has good stereochemistry (rms deviation of bond lengths from standard values of 0.018 A) and gives a crystallographic R value of 0.196 for 43,525 reflections in the range 7.5-2.1-A resolution. The copper coordination is different in the two binding sites. In the N-terminal site, the geometry is square pyramidal, with equatorial bonds to Asp 60, Tyr 192, His 253, and a monodentate anion and a longer apical bond to Tyr 92. In the C-terminal site, the geometry is distorted octahedral, with bonds to Asp 395, Tyr 435, Tyr 528, and His 597 and an asymmetrically bidentate anion. The protein structure is the same as for the diferric protein, Fe2Lf, demonstrating that the closure of the protein domains over the metal is the same in each case irrespective of whether Fe3+ or Cu2+ is bound and that copper could be transported and delivered to cells equally well as iron. The differences in metal coordination are achieved by small movements of the metal ion and anion within each binding site, which do not affect the protein structure.

Binding Sites↗
PubMed1992

Human melanotransferrin (p97) has only one functional iron-binding site.

The iron-binding properties of melanotransferrin, the tumour-associated antigen also known as p97, have been investigated by UV/visible and fluorescence spectroscopy, amino acid sequence comparison, and modelling. These show that, in contrast to other transferrins, melanotransferrin binds only one Fe3+ ion per molecule. The binding properties of its N-terminal site are similar to other transferrins, but its C-terminal site does not bind iron at all. The differences can be related to specific amino acid changes in the C-terminal site.

Antigens, Neoplasm↗
PubMed1992

Sequential paraformaldehyde and methanol fixation for simultaneous flow cytometric analysis of DNA, cell surface proteins, and intracellular proteins.

A cell fixation and permeabilization procedure consisting of sequential paraformaldehyde and methanol was evaluated and found suitable for concomitant flow cytometric quantification of total cellular DNA, immunofluorescence measurements of cell surface proteins, and immunofluorescence measurements of intracellular proteins. Paraformaldehyde/methanol-fixed cells exhibited significantly greater intracellular antitubulin immunofluorescence than cells fixed with paraformaldehyde or methanol alone (p less than 0.002) and significantly greater intracellular antitubulin immunofluorescence than cells fixed with methanol followed by paraformaldehyde (p less than 0.006). With paraformaldehyde/methanol fixation, cell morphology was well preserved and forward and right angle light scatter properties were sufficiently well maintained to permit gating on these parameters. Cell surface marker staining with fluorescent anti-leukocyte antibodies was unaffected by fixation with paraformaldehyde/methanol. Paraformaldehyde effects on the intensity of DNA staining with propidium iodide were dependent on paraformaldehyde concentration and fixation temperature; these effects were least pronounced at low paraformaldehyde concentrations (0.25% or less), and at temperatures lower than 37 degrees C. Paraformaldehyde fixation may result in differences in propidium iodide staining of DNA in some diploid cells, which may produce small spurious aneuploid peaks in normal peripheral blood leukocytes. Paraformaldehyde fixation also produces an apparent increase in the DNA index of aneuploid cell populations in comparison with methanol fixation, particularly when the DNA index exceeds 1.5. Occasionally, this paraformaldehyde fixation-induced effect is useful in identifying biologically distinct near-diploid subpopulations in tumors.

Aneuploidy↗