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Biomedical subjects

J B Smith

Publications and source records attributed to J B Smith.

At least 343 records · Page 19Linked to original sources
PubMed1983

DNA density in mitotic and meiotic metaphase chromosomes of plants and animals.

Studies of chromosome disposition at metaphase using serial thin-sectioning and three-dimensional reconstruction techniques have produced accurate estimates of the total volume of chromosomes per cell in 15 plant and two animal species. Comparing this character with the 4C DNA amount showed no indiction of systemic differences in DNA density between either organisms with widely different (greater than 200-fold) C values or different groups or organisms. For example, there was no significant difference between the density of DNA in somatic metaphase chromosomes of man (0.141 pg/micrometers3) and its mean in 14 angiosperm plant species (0.182 pg/micrometers3), or between four dicotyledons (0.180 pg/miocrometers3) and 10 monocotyledons (0.182 pg/micrometers3). However, evidence was found showing that DNA density can vary significantly within a species. Thus, although the total chromosome volume per cell was closely correlated (r greater than 0.97) with 4C DNA amount in somatic and meiotic cells, the density of DNA in metaphase chromosomes was significantly lower in meiocytes (0.131 pg/micrometers3) than in somatic metaphase cells (0.19 pg/micrometers3).

Animals↗
PubMed1983

Human platelet secreted proteins and prostacyclin production by bovine aortic endothelial cells.

The effects of specific human platelet-secreted proteins on prostacyclin (PGI2) production by primary cultures of bovine aortic endothelial cells have been studied. Cells were incubated with various concentrations of highly purified preparations of platelet factor 4 (PF4), low-affinity platelet factor 4 (LA-PF4), beta-thromboglobulin (beta TG), platelet basic protein (PBP), and partially purified platelet-derived growth factor (PDGF) in the presence or absence of arachidonic acid (AA). The amount of 6-Keto-PGF1 alpha, the stable degradation product of PGI2, was determined in the cell incubation medium by means of a specific radioimmunoassay. Short-term (15 min) incubation of cell monolayers with either LA-PF4 or beta TG slightly reduced 6-keto-PGF1 alpha production. The effect was not dose-related and could not be observed after prolonged (24 hr) incubation of the cells with the same proteins. It was not seen in the cell suspensions. Moreover, 6-keto-PGF1 alpha production stimulated by AA was not affected by incubation with either of the proteins. PF4 and PBP had no significant effect on 6-keto-PGF1 alpha production by endothelial cells. Human PDGF showed a slight tendency to stimulate 6-keto-PGF1 alpha release when cells were incubated for 24 hr with the protein; however, PDGF did not potentiate the stimulatory effect of AA on 6-keto-PGF1 alpha release by the cells. We suggest that platelet-derived proteins exert only a moderate and possibly nonspecific effect on PGI2 production by endothelial cells.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

The effect of diet on ouabain binding to erythrocytes from obese subjects.

Ouabain binding to erythrocyte membranes is increased in obese subjects. Three study groups are compared: 14 reference subjects, 102 +/- 16% of ideal weight; 9 obese on unrestricted diets, 207 +/- 16% of ideal weight; 11 obese on restricted diets, 202 +/- 35% of ideal weight. A reproducible (CV = 11.3%) ouabain-binding assay is used to measure Na+-K+ ATPase sites in erythrocyte membranes. The number of binding sites per red blood cell for obese subjects on unrestricted diets, 431 +/- 30, is greater than for the reference group, 346 +/- 66 (p less than 0.01), or for obese subjects on restricted diets, 371 +/- 68 (p less than 0.05). These data suggest that caloric intake influences the number of Na+-K+ ATPase sites. Scatchard plots indicate only one type of binding site for ouabain with an affinity constant of about 3 X 10(8) M-1.

Adolescent↗
PubMed1983

Frequency in human peripheral blood of T cells which respond to self, modified self and alloantigens.

The frequency of occurrence in human peripheral blood of T cells able to proliferate in the autologous mixed lymphocyte reaction (AMLR), and in response to trinitrophenyl (TNP)-modified self (AMLR-TNP) and alloantigens, was measured by limiting dilution analysis. AMLR responder cells were found to have a precursor frequency of from 1/7500 to 1/44,000 peripheral blood T cells. T cells able to respond to hapten modified self were about twice as common and those responding to alloantigen had a 10-fold greater frequency. Responses of T cells remaining after Budr plus light treatment of AMLR or AMLR-TNP-activated T cells indicate that these T cells are in overlapping populations. Their relation to alloreactive T cells is not clear at present. Although responses to alloantigens remained, and indeed were slightly enhanced, after Budr plus light treatment of self-reactive T cells, the experimental design does not rule out the possibility that some self-reactive T cells are also alloreactive.

Bromodeoxyuridine↗
PubMed1983

Evaluation of electrical aggregometry: comparison with optical aggregometry, secretion of ATP, and accumulation of radiolabeled platelets.

Platelet aggregation has been most commonly studied in vitro by measuring increases in light transmission as platelets aggregate in PRP. Recently, an electrical impedance method for measuring platelet aggregation has been introduced. This method can be used with either PRP or whole blood and measures an increase in impedance across electrodes placed in the blood samples as platelets accumulate on them. We have compared the results obtained by the two methods, using ADP and collagen as aggregating agents, and also have measured the secretion of platelet ATP simultaneously. Although the aggregometry results were similar, recordings obtained by the electrical method did not distinguish two waves of platelet aggregation or correlate with secretion as well as recordings obtained by the optical method. When PGI2 or PGE1 was added to the PRP, both the rate and extent of the increase in light transmittance were inhibited, but the main effect on the increase in impedance was a decrease in its rate and not in its extent. Increases in impedance and secretion of ATP were also measured in whole blood after the platelets had been labeled with a 125I-containing antibody specific for platelet surface glycoproteins. It appeared that the increases in impedance lagged several minutes behind the formation of platelet aggregates and the secretion of platelet ATP. It is suggested that there are advantages and disadvantages to both methods of measurement of platelet aggregation and that the parameters being measured must be clearly understood to properly interpret the results.

Adenosine Triphosphate↗
PubMed1983

Ontogeny of interleukin 2 responsive cells in the fetal thymus.

The ontogeny of IL 2-responsive cells in the thymus of CBA/J mice was examined in neonatal animals and in fetuses at 14, 16, and 18 to 20 days gestation. The thymocytes were tested for responsiveness to 2 micrograms/ml Con A, TCGF, IL 2, and co-stimulation by Con A plus TCGF or IL 2. These responses were compared with those of thymocytes of 6- to 8-wk-old CBA/J. Thymocytes (1 X 10(5)) were cultured, and the reaction was measured at maximum response (96 hr). Neonatal animals gave an unusually high response to TCGF or partially purified IL 2 alone, approximately five times greater than the adult. A low but significantly enhanced proliferation, stimulated by partially purified IL 2 alone, was observed with 14-day fetal thymocytes, even though cultures of these cells in medium alone had higher background proliferation than any other age tested. In the co-stimulator reaction, proliferation significantly above background was measured at 16 days of gestation with Con A plus TCGF. The magnitude of the co-stimulator reaction increased with age, especially between the 16th and 18th day of gestation and immediately after birth.

Animals↗
PubMed1982

Helper cells in the autologous mixed lymphocyte reaction. III. Production of helper factor(s) distinct from interleukin 2.

In normal mice, the autologous mixed lymphocyte reaction (AMLR) can activate helper T cells that, in the presence of hapten-modified syngeneic cells, can induce a hapten-specific cytotoxic response. Supernatants from AMLR cultures contain a factor(s) that will mediate a cytotoxic T cell response to hapten-altered self. The AMLR factor is effective in facilitating the generation of cytotoxicity only in those cultures containing both T cells and hapten-altered, syngeneic, nonstimulatory cells. Factor production requires an interaction between Lyt-1+23- cells and non-T cells (the T cells synthesize it). The AMLR factor does not appear to be interleukin 2 (IL-2) because it does not activate thymocytes in the presence of antigen, nor does it maintain an IL-2-dependent cell line or function in co-stimulator assays. For the AMLR factor to facilitate the generation of cytotoxicity, thymic adherent cells are a necessary intermediate. These data suggest that the factor recoverable from AMLR cultures acts early in the cytotoxic pathway, before IL-1 production.

Animals↗
PubMed1982

Effect of thromboxane synthetase inhibitors on platelet function: enhancement by inhibition of phosphodiesterase.

The effects of several selective thromboxane synthetase inhibitors, alone and in combination with inhibitors of cyclic AMP phosphodiesterase, on the aggregation of human platelets in response to collagen, ADP, 1-0-alkyl-2-acetyl-sn-glycerophosphocholine (1-alkyl-2-acetyl-GPC), 9,11-azo-PGH2 and sodium arachidonate were studied in vitro. The thromboxane synthetase inhibitors caused little or no inhibition of aggregation at the concentrations used, while the phosphodiesterase inhibitors caused partial to complete inhibition of aggregation induced by all of the aggregating agents, with anagrelide being the most potent inhibitor and sodium arachidonate the agent most susceptible to inhibition. Combination of inhibitors of thromboxane synthetase with inhibitors of cyclic AMP phosphodiesterase, at concentrations of each which caused little or no effect when used alone, produced marked inhibition of platelet aggregation induced by collagen or arachidonic acid but not by the other aggregating agents studied. This interaction between the two classes of inhibitors appears to be due to the accumulation of cyclic AMP as it can be reversed by 9-(tetrahydro-2-furyl) adenine, an inhibitor of adenylate cyclase. Furthermore, as no synergistic inhibition was found using aggregating agents that are poor inducers of thromboxane formation, or using collagen after the ingestion of aspirin, it is most likely that activation of adenylate cyclase occurs because of diversion of thromboxanes into prostaglandins particularly PGD2. The present results suggest that combined use of inhibitors of thromboxane synthetase and inhibitors of cyclic AMP phosphodiesterase may provide a new approach to antithrombotic therapy.

Adenine↗
PubMed1982

Phospholipid biosynthesis in human platelets. Formation of phosphatidylcholine from 1-acyl lysophosphatidylcholine by acyl-CoA:1-acyl-sn-glycero-3-phosphocholine acyltransferase.

Arachidonic acid and other fatty acids are taken up by human platelets from plasma and incorporated into membrane phospholipids. However, little is known about the mechanism and specificity of the various steps of fatty acid insertion into phospholipid. Previous findings from this laboratory have shown that the incorporation of radioactive C20-unsaturated fatty acids (arachidonic, 8,11,14-eicosatrienoic, and 5,8,11,14,17-eicosapentaenoic) into the phospholipids of "resting"p platelets is more rapid than that of the radioactive C16- and C18-saturated and unsaturated fatty acids. We now provide evidence that human platelet microsomes contain acyl-CoA:1-acyl-sn-glycero-3-phosphocholine acyltransferase. The enzyme preparation has a pH optimum of 7.0. Activity is insensitive to 1 mM EDTA and is inhibited 37% by 1 mM Ca2+ and 20% by 1 mM Mg2+. Maximal activity is observed at 100 microM 1-acyl lysophosphatidylcholine at several concentrations of fatty acyl-CoA esters. Apparent Km values from 1.05 to 5.70 microM were obtained for saturated and unsaturated fatty acyl group donors in the presence of 100 microM 1-acyl lysophosphatidylcholine as fatty acyl group acceptor. Comparison of the apparent Vmax values showed that unsaturated CoA esters were transferred more rapidly to 1-acyl lysophosphatidylcholine than saturated CoA esters. Oleate, linoleate, and arachidonate, the major unsaturated fatty acids in platelet phosphatidylcholine, were transferred at similar rates. 8,11,14-eicosatrienoate was transferred about two times faster than these three fatty acyl groups. The data indicate that the incorporation of unsaturated fatty acids into phosphatidylcholine by human platelets occurs via reacylation of 1-acyl lysophosphatidylcholine.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1982

Regulation of arachidonate-induced platelet aggregation by the lipoxygenase product, 12-hydroperoxyeicosatetraenoic acid.

The lipoxygenase product, 12-hydroperoxyeicosatetraenoic acid (12-HPETE) was biosynthesized, purified and incubated with washed human platelet. It inhibited arachidonic acid, azo-prostaglandin H2 or U-46619-induced aggregation and secretion in a concentration-dependent fashion (IC50 = 2-3 microM). Collagen-induced aggregation and secretion were also inhibited (IC50 = 6 microM). 12-HPETE inhibited malondialdehyde and thromboxane B2 formation in platelets stimulated with arachidonic acid or thrombin. While thrombin-induced aggregation was unaffected by 50 microM 12-HPETE, thrombin-induced secretion was inhibited. Inhibiton of secretion by 12-HPETE was observed in platelets from untreated as well as aspirin-treated donors, indicating that 12-HPETE inhibits secretion independently of its ability to inhibit prostaglandin formation. Aggregation of washed human platelets by arachidonic acid yielded a bell-shaped concentration-response curve. Diminished aggregation at higher concentrations was associated with an increase in the ratio of lipoxygenase products to thromboxane B2. The data suggest that 12-HPETE formation may regulate platelet aggregation and secretion and that its primary effect, at low concentrations, is inhibition of endoperoxide-induced responses. At higher concentrations 12-HPETE also inhibits arachidonic acid metabolism. Thus, the combined inhibitory effects on endoperoxide-induced aggregation and thromboxane formation would explain the diminished aggregation observed in response to high concentrations of arachidonic acid.

Adenosine Triphosphate↗
PubMed1982

Reversible stimulation of the Na+/K+ pump by monensin in cultures of vascular smooth muscle.

Two ionophores, monensin and salinomycin, increased total cell Na+ and ouabain-sensitive 86Rb+ uptake in cultures of smooth muscle cells from rat aorta. Monensin was used to produce graded increases in cell Na+ in order to assess the Na+ dependence of the Na+/K+ pump in the intact cell. The relationship between internal Na+ and ouabain-sensitive 86Rb+ uptake was hyperbolic (K'Na = 3 mM). Monensin did not stimulate 86Rb+ uptake in the absence of external Na+. Loading the cells with Na+ by exposing cultures to a K+-free medium for 3 hr maximally increased cell Na+ and ouabain-sensitive 86Rb+ uptake to the same extent as monensin. Total cell Na+ and pump activity in monensin-treated cells returned to the initial values after removing the ionophore. Monensin was then able to increase total cell Na+ and ouabain-sensitive 86Rb+ uptake to the same extent as the initial treatment with the ionophore.

Animals↗
PubMed1982

Radioimmunologic identification of prostaglandins produced by serum-stimulated mouse embryo palate mesenchyme cells.

High-performance liquid chromatography and radioimmunoassay were used to identify the prostaglandins synthesized by mouse embryo palate mesenchyme cells. Serum stimulated the release of several different metabolites of arachidonic acid including 6-ketoprostaglandin F1 alpha (the stable product of prostacyclin, prostaglandin I2), prostaglandin E2 and prostaglandin F2 alpha. Compared to control cells, the serum-stimulated cells produce elevated levels of prostaglandin E2 (36-fold), 6-ketoprostaglandin F1 alpha (15-fold) and prostaglandin F2 alpha (7-fold). The acetylenic analogue of arachidonic acid, 5,8,11,14-eicosatetraynoic acid prevented this accelerated synthesis.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1982

A reproducible sodium-lithium countertransport assay: the outcome of changing key laboratory parameters.

This paper describes experimental conditions for reproducible measurement of sodium-lithium countertransport in red blood cells. The assay is sensitive to temperature (10% per degree C) and the condition of the red cells; it is affected little by changes in intracellular lithium over the range 2-7 mmol/1 or by red cell concentrations with laboratory hematocrits of 0.03 to 0.07. Repeated measurements of the same subjects give day-to-day coefficients of variation of 10% or less. The mean difference for interlaboratory comparisons is 11%.

Biological Transport↗
PubMed1982

A kinetic expression for sodium-lithium countertransport in human red cells.

Sodium-lithium counter-transport in human red blood cells may be a potentially useful measurement in studies of hypertension. A kinetic expression describing this counter-transport was derived and evaluated using red cells from nine subjects at various concentrations of intracellular and extracellular Li+ and Na+. The countertransport is dependent upon all four concentrations, intracellular Li+ and Na+ as well as extracellular Li+ and Na+. We confirm that the maximum Na+-Li+ counter-transport (Vmax) is a property of the individual cells while the half-maximal saturating concentrations (K 1/2) for Li+ and Na+ are the same for all subjects. This expression permits a more thorough understanding of conditions affecting Na+-Li+ countertransport measurement.

Biological Transport↗