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Biomedical subjects

D S Smith

Publications and source records attributed to D S Smith.

At least 217 records · Page 12Linked to original sources
PubMed1987

N-methyl-N'-nitro-N-nitrosoguanidine-induced resistance to ionizing radiation.

N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) pretreatments increase the resistance of Escherichia coli to gamma-radiation. The increased resistance is dependent on functional polA, recA, recB, recC, and lexA genes and is partly dependent on recN. The MNNG-induced resistance is additive to resistance induced by pretreatment with gamma-radiation but not by increases induced by hydrogen peroxide. The MNNG-induced resistance occurs in adaptive response mutants and at pretreatment levels of MNNG that do not activate cells to reactivate UV-inactivated lambda phage. The MNNG-induced resistance appears to be distinct from other inductions to gamma-radiation resistance.

Escherichia coli↗
PubMed1987

Barium spikes are generated in the spines of the sea urchin Diadema antillarum.

In the presence of calcium, Ba2+ ions, at concentrations as low as 1-2 mM, block the action potentials (a.p.'s) elicited by the electrical stimulation of the primary spines of Diadema antillarum. Lower concentrations of barium (0.1 mM) potentiate the a.p.'s recorded from spines equilibrated with Ca-Free artificial sea water (ASW). Exposure of the spines to a saturated solution of EDTA in Ca-free, unbuffered ASW reversibly blocks their electrical activity. Spines blocked by EDTA continue to generate a.p.'s following their equilibration with Ca-free ASW containing 1 mM of Ba2+ ions. The time course of the a.p.'s recorded from spines equilibrated with normal ASW is only slightly affected by the combined action of 15 mM of tetraethylammonium (TEA) and 5 mM of 4-aminopyridine (4-AP). In contrast, the duration of the a.p.'s recorded from spines blocked by EDTA and placed in 1 mM barium is markedly increased by the combined actions of TEA and 4-AP at the above concentrations. We conclude that the Ca-channels of the neurites present in Diadema spines are not, at least qualitatively, an exception with regard to their permeation by Ba2+. The blocking action of low concentrations of these ions, particularly in the presence of calcium, may be explained by the extremely high surface to volume ratio prevailing in neurites with a diameter of only less than 0.1-0.3 micron.

4-Aminopyridine↗
PubMed1987

Radioimmunoassay of salivary digoxin by simple adaptation of a kit method for serum digoxin: saliva/serum ratio and correlation.

A robust commercial radioimmunoassay kit for serum digoxin was adapted to salivary assay by simple procedural modifications and shown to have satisfactory sensitivity, precision, accuracy, and specificity. The digoxin saliva/serum concentration ratio in 50 hospital patients was 0.67 +/- 0.10 (mean +/- SD), and the levels were well correlated (r = 0.96). Similar saliva/serum ratios were found in two normal subjects who took digoxin orally, and the free fraction in serum, determined by equilibrium dialysis, was found to equate with the salivary drug level. Digoxin appeared in saliva at its maximum level within 1 min of intravenous injection. Although previous studies of salivary digoxin have given widely discrepant results, the present findings are entirely consistent with the simple expectation that digoxin should appear in saliva by passive diffusion. Salivary sampling is suitable for the monitoring of digoxin therapy and pharmacokinetics, and the modified radioimmunoassay should be of value to laboratories wishing to introduce this technique.

Digoxin↗
PubMed1987

An autoantibody with activity dependent on red cell age in the serum of a patient with autoimmune haemolytic anaemia and a negative direct antiglobulin test.

A red cell IgM autoantibody with anti-e specificity was identified in the serum of a rhesus-negative (rr) patient presenting with haemolytic anaemia and a negative direct antiglobulin test. The autoantibody strongly agglutinated normal allogeneic rhesus-negative (rr) red cells in saline at 37 degrees C but had only weak activity for autologous red cells. Incubation of the patient's serum with subpopulations of normal allogeneic red cells obtained by density fractionation, demonstrated that the strong agglutinating activity of the autoantibody was for red cells with density greater than 1.090 g/ml. Young red cell subpopulations of lower density gave weak reactions and low titration scores equivalent to those obtained with autologous red cells during the haemolytic episode. The patient's red cells during remission however, when the patient's haemoglobin level had returned to normal, were strongly agglutinated by serum samples taken during the haemolytic episode; as was the case with normal allogeneic red cells, the strong activity was for patient red cells with density greater than 1.090 g/ml, red cell populations of lower density giving low titration scores. The findings in this case indicate that the patient's red cells which had survived haemolysis during the haemolytic episode were young red cells (density less than 1.090 g/ml), the weak sensitization of these cells being insufficient to cause their destruction by macrophages. Furthermore, these findings, together with observations that IgG autoantibodies may also bind less strongly to young red cells [Gray et al., Br. J. Haemat., 55: 335-345, 1983; Branch et al., Blood 63: 177-180, 1984].(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia, Hemolytic, Autoimmune↗
PubMed1987

An approach to the problem of metabolic heterogeneity in brain: ischemia and reflow after ischemia.

We have proposed that tissue metabolic failure during hypoxia or ischemia is related to the microheterogeneous distribution of tissue oxygen and not to failure of the creatine kinase equilibrium. This theory is based on the concept that sharp oxygen gradients exist in rapidly metabolizing tissue and that shifts in these gradients can place specific cells at risk for metabolic death while relatively adjacent cells escape unharmed; cells that are unharmed meet the steady-state requirements (V less than Vmax), those at risk do not (V greater than Vmax). Though it would seem that confirmation of such a hypothesis would require metabolic delineation at a high resolution, we have shown how 31P MRS provides information supporting this hypothesis. This possible use of MR spectroscopy to define microheterogeneous events suggests further clinical possibilities for this instrument in defining the rate of cell loss and the response to therapeutic interventions.

Animals↗
PubMed1987

Single-reagent polarization fluoroimmunoassay of methamphetamine in urine.

We developed a polarization fluoroimmunoassay for the specific detection of methamphetamine in urine. Sheep antiserum raised against methamphetamine was premixed with a fluorescein-labeled amphetamine tracer in a single reagent. The use of labeled amphetamine gave a more sensitive and more specific assay than did the use of a labeled methamphetamine tracer. The assay system had equal sensitivity for the d- and l-isomers of methamphetamine while the cross reactivity of amphetamine and other structurally related compounds was 3% or less. With a positive/negative cutoff concentration set at 1 mg/L, the polarization fluoroimmunoassay reliably identified human urines that had been reported positive for methamphetamine by an established gas-liquid chromatographic method.

Animals↗
PubMed1986

Effects of intraoperative glucose on protein catabolism and plasma glucose levels in patients with supratentorial tumors.

Animal studies suggest that hyperglycemia (glucose concentrations greater than 225 mg/dl) occurring prior to periods of brain ischemia exacerbates neurologic damage. Neurosurgical patients, a group at risk for intraoperative brain ischemia, often receive glucose. Therefore, the effects of intraoperative glucose administration (IGA) on these patients were studied. Sixteen patients undergoing supratentorial craniotomy were randomly assigned to receive either 5% glucose in 0.9% sodium chloride solution (G) or 0.9% sodium chloride solution (S) infusion (both at a rate of 3-4 ml X kg-1 X h-1) during the first 4 h of surgery. All patients received glucose infusions postoperatively. Plasma glucose, insulin, free fatty acids, alanine, ketones, base excess, pH, triglycerides, and lactate were measured during the infusion period and 24 h postoperatively. Urinary nitrogen was measured, commencing with the infusion and continuing for 24 h. Neurologic testing included preoperative and postoperative neurologic and psychomotor exams, time to extubation (min), and degree of alertness at the completion of anesthesia. The G group had significantly greater intraoperative plasma glucose concentrations at all time periods studied during the infusion (P less than 0.05). Glucose levels ranged from 200-242 mg/dl compared with 120-160 mg/dl in G and S groups, respectively. G group hyperglycemia was within the range associated with exacerbation of ischemic brain damage in animal studies. Free fatty acids and ketones were significantly greater (P less than 0.05) intraoperatively in the S group. Lactate and insulin were significantly greater in the G group at 4 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Single-reagent polarization fluoroimmunoassay for theophylline in serum.

A polarization fluoroimmunoassay for theophylline was developed employing fluorescein-labeled drug and antiserum precombined in a single reagent. Assay was performed simply by addition of sample to an aliquot of the single reagent, incubation, and determination of fluorescence polarization. Because of the relatively rapid dissociation kinetics of the labeled drug from antibody binding, added unlabeled theophylline caused displacement within a practical time period. The precision, accuracy, and specificity of the simplified single-reagent assay were similar to those obtained by a conventional immunoassay procedure using the same reagents. Results for the assay of patients' serum specimens correlated well with those by an established enzymoimmunoassay.

Animals↗