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Biomedical subjects

C J Smith

Publications and source records attributed to C J Smith.

At least 199 records · Page 11Linked to original sources
PubMed1992

Environmental tobacco smoke: current assessment and future directions.

Scientific information on environmental tobacco smoke (ETS) is critically reviewed. Key areas addressed are: differences in chemical composition between mainstream smoke, sidestream smoke, and ETS; techniques for measurement of ETS; epidemiology; in vitro and in vivo toxicology; and chamber and field studies of perceptual or physiological effects. Questions concerning estimation of ETS exposure, suitability of various biomarkers, calculation of lifetime dose, control of confounding variables, use of meta-analysis, and the relationship between ETS concentrations and human responses all emphasize the need for additional research in order to assess potential effects of ETS on health or comfort.

Animals↗
PubMed1992

Leucocyte migration: effects of in vitro exposure to anaesthetic agents: possible potentiation of effects by adrenaline.

The effect on in vitro migration of leucocytes and lymphocytes of various drugs used in anaesthesia have been determined in the concentration range 10(-2) to 10(-6) M. The drugs included, thiopentone, bupivacaine, lignocaine, adrenaline, noradrenaline, hydrocortisone, morphine (with and without preservative), lorazepam, suxamethonium, pancuronium and atropine. Toxicity and effect on random mobility after incubation for 1 and 18 h were also determined. Thiopentone depressed leucocyte function at a concentration of 10(-5) M which is comparable to clinical plasma concentrations. Increasing the duration of exposure of the cells to the drugs significantly lowered the concentrations at which depression of function was observed. At concentrations used during local infiltration in clinical practice, bupivacaine and lignocaine were toxic to both leucocytes and lymphocytes. Adrenaline, whilst having no direct effect on cell function, potentiated the effect of lignocaine. Morphine showed no effect at 10(-4) M, a level 1,000 times greater than the reported toxic plasma levels. However, this level falls within the range reported for drug addicts. No effects were found for the other drugs.

Adult↗
PubMed1991

Binding of a chaperonin to the folding intermediates of lactate dehydrogenase.

When Bacillus stearothermophilus LDH dimer is incubated with increasing concentrations of the denaturant guanidinium chloride, three distinct unfolded states of the molecule are observed at equilibrium [Smith, C. J., et al. (1991) Biochemistry 30, 1028-1036]. The kinetics of LDH refolding are consistent with an unbranched progression through these states. The Escherichia coli chaperonin, GroEL, binds with high affinity to the completely denatured form and more weakly to the earliest folding intermediate, thus retarding the refolding process. A later structurally defined folding intermediate, corresponding to a molten globule form, is not bound by GroEL; neither is the inactive monomer. The complex between GroEL and denatured LDH is destabilized by the binding of magnesium/ATP (Mg/ATP) or by the nonhydrolyzable analogue adenylyl imidodiphosphate (AMP-PNP). From our initial kinetic data, we propose that GroEL exists in two interconvertible forms, one of which is stabilized by the binding of Mg/ATP but associates weakly with the unfolded protein. The other is destabilized by Mg/ATP and associates strongly with unfolded LDH. The relevance of these findings to the role of GroEL in vivo is discussed.

Adenine Nucleotides↗
PubMed1991

Actin accelerates plasmin generation by tissue plasminogen activator.

Actin has been found to bind to plasmin's kringle regions, thereby inhibiting its enzymatic activity in a noncompetitive manner. We, therefore, examined its effect upon the conversion of plasminogen to plasmin by tissue plasminogen activator. Actin stimulated plasmin generation from both Glu- and Lys-plasminogen, lowering the Km for activation of Glu-plasminogen into the low micromolar range. Accelerated plasmin generation did not occur in the presence of epsilon-amino caproic acid or if actin was exposed to acetic anhydride, an agent known to acetylate lysine residues. Actin binds to tissue plasminogen activator (t-Pa) (Kd = 0.55 microM), at least partially via lysine-binding sites. Actin's stimulation of plasmin generation from Glu-plasminogen was inhibited by the addition of aprotinin and was restored by the substitution of plasmin-treated actin, indicating the operation of a plasmin-dependent positive feedback mechanism. Native actin binds to Lys-plasminogen, and promotes its conversion to plasmin even in the presence of aprotinin, indicating that plasmin's cleavage of either actin or plasminogen leads to further plasmin generation. Plasmin-treated actin binds Glu-plasminogen and t-PA simultaneously, thereby raising the local concentration of t-PA and plasminogen. Together, but not separately, actin and t-PA prolong the thrombin time of plasma through the generation of plasmin and fibrinogen degradation products. Actin-stimulated plasmin generation may be responsible for some of the changes found in peripheral blood following tissue injury and sepsis.

Actins↗
PubMed1991

Hormone-sensitive cyclic GMP-inhibited cyclic AMP phosphodiesterase in rat adipocytes. Regulation of insulin- and cAMP-dependent activation by phosphorylation.

In 32PO4-labeled adipocytes, isoproterenol (ISO) or physiologically relevant concentrations of insulin rapidly increased phosphorylation of a particulate 135-kDa protein which has been identified as a cGMP-inhibited "low Km" cAMP phosphodiesterase (CGI-PDE) by several criteria, including selective immunoprecipitation with anti-CGI-PDE IgG (Degerman, E., Smith, C.J., Tornqvist, H., Vasta, V., Belfrage, P., and Manganiello, V.C. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 533-537). The time courses and concentration dependences for phosphorylation of CGI-PDE by ISO and insulin correlated with CGI-PDE activation in the presence of these agents; effects of ISO were somewhat more rapid than those of insulin. Adenosine deaminase, which metabolizes the adenylate cyclase inhibitor adenosine, also rapidly induced phosphorylation and activation of CGI-PDE. Phenylisopropyladenosine (an adenosine deaminase-resistant adenosine analog) prevented or reversed both adenosine deaminase-stimulated phosphorylation and activation of CGI-PDE (IC50 approximately 0.2 nM). Incubation of adipocytes with 0.1 nM insulin in the presence of ISO rapidly produced 30-200% greater activation and phosphorylation of CGI-PDE than the expected added effects of insulin and ISO individually; both effects preceded the insulin-induced decreases in protein kinase A activity and inhibition of lipolysis. These and other results indicate that CGI-PDE can be phosphorylated at distinct sites and activated by cAMP-dependent and insulin-dependent serine kinase(s), that the activation state of CGI-PDE reflects its relative phosphorylation state, and that synergistic phosphorylation/activation of CGI-PDE may be important in the antilipolytic action of insulin.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Actin is a noncompetitive plasmin inhibitor.

Actin, one of the most abundant cellular proteins, circulates at micromolar concentrations in peripheral blood. Because actin released from dying cells may be trapped in fibrin clots that form at sites of tissue injury, we examined the effects of actin upon lysis of fibrin clots in vitro. Incorporation of native rabbit skeletal muscle actin into fibrin clots slowed their rates of lysis for periods of up to 24 h, an effect not seen when comparable concentrations of human IgG or bovine serum albumin were added instead. Actins isolated from a variety of sources inhibited plasmin's hydrolysis of the synthetic substrate S-2251 in a noncompetitive manner, with a Ki of a 0.6-3.1 microM. Inhibition was rapid, but covalent actin-plasmin complexes were not formed. Both epsilon-aminocaproic acid and tranexamic acid prevented actin's inhibition of plasmin, suggesting that accessible lysine residues of actin interact with the kringle (lysine-binding) regions of plasmin. Neither of the high-affinity actin-binding proteins of plasma (plasma gelsolin and vitamin D-binding protein) prevented actin from inhibiting plasmin. These findings suggest that actin released into the extracellular space following cell death may modulate plasmin action, and hence a number of plasmin-dependent biological responses, at sites of inflammation and tissue injury.

Actins↗
PubMed1991

Detection and characterization of intermediates in the folding of large proteins by the use of genetically inserted tryptophan probes.

L-Lactate dehydrogenase from Bacillus stearothermophilus was rebuilt by using site-directed mutagenesis to produce an enzymically active, tryptophan-less enzyme by replacing all the wild-type tryptophans (80, 150, and 203) by tyrosines. Nine single tryptophan-containing active enzymes were constructed from this enzyme by genetically replacing one of the tyrosines 36, 85, 147, 190, 203, 237, 248, 279, or 285 by tryptophan. The equilibrium and the time-resolved tryptophan fluorescence intensity and anisotropy were used to report unfolding events in guanidine hydrochloride (GHCl) monitored from these nine defined positions. Three structural transitions, half complete at 0.55, 1.7, and 2.8 M GHCl, were identified and defined four folding intermediates, I (native), II (expanded monomer 1), III (expanded monomer 2), and IV (random coil), stable at 0, 1, 2.2, and 4 M GHCl, respectively. Intermediate II is a globular monomer. All the probed alpha-helices and most of the beta-structure was intact. There was an increase in the rate but not the extent of the mobilities of six of the probed tryptophan side chains, indicating loss of tertiary structure. Circular dichroism (CD) showed all the secondary structure to be intact. Intermediate III is monomeric and still globular, but the tryptophan anisotropy indicated an increase mobility at positions 36, 85, 190, 203, 279, and 285. Helix alpha-B is further disrupted but helices alpha-1F, alpha-2G, and alpha 3G were still rigid. CD showed half the secondary structure to be still intact. Intermediate IV is a random coil in which all tryptophans have complete rotational freedom and the helix CD signal is lost.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Characterization of p51/52, a cell-growth regulated protein of WI-38 cells.

A number of proteins have been identified whose expression or activity is regulated by cell growth. We have produced a monoclonal antibody against a new cell-growth regulated protein found in normal human fibroblasts. We have shown that this antibody recognizes a 51/52-kDa doublet (p51/52) found mainly in normal cells. This doublet is sensitive to degradation by the calcium-activated protease, calpain, breaking down to a 37/38-kDa doublet. The relative amount of the two members of the 51/52-kDa doublet changes when serum-starved cells reenter the cell cycle. Quiescent cells express mainly the 51-kDa form; the 52-kDa form becomes more abundant upon refeeding serum-starved cells. Transformed cells express either very small amounts of this doublet, and then predominantly the 52-kDa form, or no detectable amount of either form. These characteristics distinguish this molecule from several other known growth-regulated proteins such as statin and the anti-oncogene p53.

Antibodies, Monoclonal↗
PubMed1991

Time-dependent biphasic effect of cytochalasin D on luteal progesterone release in the pregnant rat.

Numerous studies have examined the effects of cytoskeletal disruption on steroidogenesis; while some report an inhibition, other studies show a stimulation of steroid hormone production. In the present study, the possibility of a biphasic effect of cytoskeletal inhibitors on steroidogenesis was examined. Luteal tissue from day 12 pregnant rats was incubated for either 3.5 h (short-term) or 12.5 h (long-term) with cytochalasin D or colchicine at 10(-4) M in Medium 199 (medium). Controls were incubated in medium alone. After the incubation, the tissues were separated from the medium, and either processed for electron microscopy, or weighed and snap-frozen for subsequent homogenization and steroid hormone measurements. Progesterone, testosterone, and 17 beta-estradiol levels in the medium were measured by radioimmunoassay. After the short-term incubation, progesterone release decreased with cytochalasin D treatment, while cells became more rounded in shape with a loss of microfilaments. Upon long-term incubation, progesterone release increased and cell contact lessened. Colchicine had no effect at either incubation time, and estradiol and testosterone production remained unchanged throughout the experiments. These results demonstrate that cytochalasin D has a biphasic effect on luteal progesterone release in the rat and provides an explanation for the dichotomy of results thus far reported. In addition, the effects of cytochalasin D on rat luteal progesterone production appear to be the result of changes in cell shape or cell-to-cell contact.

Animals↗
PubMed1991

Nerve growth factor-induced neuronal differentiation is accompanied by differential splicing of beta-amyloid precursor mRNAs in the PC12 cell line.

The effect of the neurotrophic factor nerve growth factor (NGF) on the expression of the beta-amyloid gene has been studied in the clonal nerve cell line PC12. The neuronal differentiation of PC12 cells in the presence of NGF was accompanied by a shift in the ratio of beta-amyloid precursor protein (APP) transcripts. In particular there was reduced expression of the transcript coding for the longest precursor form (APP770) and a concomitant increase in the shortest (APP695) transcript following NGF treatment.

Amyloid beta-Protein Precursor↗
PubMed1991

Another day in paradise? Life on the margins in urban New Zealand.

This paper examines the relationships between housing and health with respect to a sample of New Zealand public housing applicants. In the first part of the paper, the notion of incipient homelessness is reviewed, the production of this population in advanced capitalist societies is considered and the social geography of the inadequately housed in New Zealand is surveyed. The second part of the paper presents some of the data collected in a survey of the inadequately housed in Auckland and Christchurch (n = 213 households). The results suggest that housing is an important determinant of the health and well-being of this population, but that rehousing the poor should be seen as only one step in addressing inequalities in contemporary urban New Zealand.

Ethnicity↗
PubMed1991

Effects of in vivo dihydrotestosterone treatment on changes in nocturnal surge of prolactin, luteal ultrastructure and P-450scc mRNA and protein content in pregnant rats.

We have demonstrated previously that the administration of dihydrotestosterone (DHT) decreases plasma progesterone levels within 24 h and thus, results in abortion during the first half of pregnancy (Am. J. Physiol. 241 (1981) E444-E448). The purpose of this study was to determine (a) if the administration of DHT suppresses plasma prolactin levels or its nocturnal surge within 24 h after the treatment, (b) how soon after the commencement of treatment do the concentrations of DHT increase and progesterone levels decrease in the circulation, (c) the ultrastructural changes that occur in corpora lutea, and (d) the changes in luteal P-450 side-chain cleavage (P-450scc) enzyme and mRNA content upon DHT treatment. Within 24 h after the commencement of DHT treatment, the nocturnal surge of prolactin, detected in both groups on day 10 at 03.30 h, was inhibited in DHT-treated rats as compared to controls. The non-surge levels of prolactin at 05.00 and 06.00 h were not different between groups. The intraovarian DHT pellet increased plasma levels of the steroid 3-fold within 2 h (blood samples were taken at 2-hourly intervals) when compared to controls. By 24 h DHT levels were decreased but were still higher than controls. Plasma progesterone levels began to fall 6 h after the commencement of treatment. Luteal tissue from animals treated with DHT appeared steroidogenic, and contained more lipid droplets than controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Changes in rat luteal ultrastructure and P450scc mRNA and protein content after in vivo treatment with a gonadotropin-releasing hormone agonist.

Previous studies have demonstrated that plasma progesterone levels decrease in pregnant rats treated in vivo with a gonadotropin-releasing hormone agonist (GnRH-Ag), without changes in testosterone or estradiol levels in ovarian vein plasma. The objective of this study was to determine the loci of GnRH-Ag disruption of progesterone synthesis by examining luteal mitochondria, lipid droplets, cellular composition, and P450 side-chain cleavage (P450scc) enzyme and mRNA content in the pregnant rat. On Day 7 or 11 of pregnancy, osmotic minipumps containing GnRH-Ag were implanted into 5-7 rats. Sham operations were performed on 5-6 controls at each time period. Five micrograms per day of GnRH-Ag were released for about 24 h, after which corpora lutea and jugular vein plasma were collected. The corpora lutea were prepared for microscopy or analyzed for P450scc enzyme and mRNA content. Plasma progesterone levels were measured by RIA. In those rats treated with GnRH-Ag, progesterone levels had decreased, and within the luteal cells, there was an increase in the number of lipid droplets and a decrease in the number of tubular cristae within the mitochondria. Concomitantly, P450scc enzyme and mRNA content decreased on both Day 8 and Day 12 of pregnancy. Also, GnRH-Ag treatment decreased the ratio of large to small steroidogenic luteal cells on Day 8 of pregnancy, but did not alter cellular ratios on Day 12 of pregnancy. These observations suggest that treatment with GnRH-Ag inhibits progesterone synthesis by decreasing the amount of P450scc mRNA and enzyme content, which may alter the mitochondrial cristae structure on Day 8 and Day 12 of pregnancy. The reduction in tubular cristae and P450scc enzyme in the mitochondria may account for the increase in lipid droplets, as less cholesterol is converted to pregnenolone. An additional mechanism of inhibition may be the reduction in the number of large steroidogenic luteal cells, which appear to be the major source of progesterone in the rat corpus luteum on Day 8 of pregnancy.

Animals↗