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Biomedical subjects

D S Smith

Publications and source records attributed to D S Smith.

At least 307 records · Page 17Linked to original sources
PubMed1980

An H-deficient blood with normal H transferase levels.

An H-deficient blood is described which, unlike other H-deficient, Bombay and para-Bombay bloods, has normal H transferase levels. In previous examples of Bombay and para-Bombay phenotypes the absence of H transferase has explained the lack of H substrate and therefore the weak A and B antigens which are characteristic of these phenotypes. This explanation obviously does not hold in the case described here and it is proposed that the biochemical block must be further back, either in the enzymes synthesising the oligosaccharide chains or in those making the GDP-fucose substrate for the H and the Le gene-specified fucosyltransferases. Inhibition of the synthesis of Leb substance, as well as H substance, although the saliva of the propositus contains the Le gene-specified transferase, supports this proposition.

ABO Blood-Group System↗
PubMed1980

Cortisol directly determined in serum by fluoroimmunoassay with magnetizable solid phase.

We developed a direct fluoroimmunoassay for cortisol in serum. This method involves cortisol labeled at the 3 position with fluorescein, and antibodies to cortisol coupled to magnetizable cellulose/iron oxide particles. Sodium salicylate is used as a blocking agent to prevent interference from endogenous binding proteins in serum. Serum sample and labeled cortisol are incubated with the antibody-coupled solid phase for 30 min. The solid phase is then separated and washed to remove free labeled cortisol and endogenous fluorophores of the sample. Finally we elute the antibody-bound fraction of the labeled cortisol into an alkaline methanolic medium and measure its fluorescence. The separation, wash, and elution steps are facilitated by magnetic sedimentation. The assay is sufficiently sensitive, specific, and reliable for routine use and correlates acceptably (r = 0.92) with an established radioimmunoassay. Precision (CV) ranged from 4 to 10% in experiments on three pooled sera; analytical recovery for sera supplemented with as much as 360 microgram of cortisol per liter was 91 to 109%.

Cross Reactions↗
PubMed1980

Barbiturates as protective agents in brain ischemia and as free radical scavengers in vitro.

Barbiturates protect the brain in several types of ischemia. The exact mechanism(s) by which they afford protection are unknown. Interest has been focused for the most part on their effects as metabolic depressants, but a slowing energy consumption rate in the ischemic brain cannot explain protection in all ischemic situations. Other propositions for the protective mechanisms of barbiturates include alterations in blood flow distribution, membrane stabilization as well as antioxidant and free radical scavenging properties. We have studied the inhibitory effects of various barbiturates on iron- and ascorbic acid-stimulated lipid peroxidation in brain tissue in vitro. While thiopental was highly efficient, other barbiturates had no (phenobarbital, pentobarbital) or only minor (methohexital) inhibitory effects. The findings were confirmed by studies of the scavenging properties of these barbiturates with a different system (1,1 diphenyl-2-picryl hydrazyl). Since all tested barbiturates protect in brain ischemia in vivo, our results do not support the hypothesis that they protect by acting as free radical scavengers.

Animals↗
PubMed1980

Reversible ischemia of the brain: biochemical factors influencing restitution.

Biochemical factors of potential importance for the development of irreversible brain cell damage in reversible ischemia may, at least theoretically, not only involve anaerobic events but also oxidative reactions. If so, such reactions should be expected to occur either if oxygen delivery to the tissue during ischemia is not totally abolished, i.e. as in incomplete ischemia, or during the recirculation phase. Several investigations have shown that pronounced incomplete brain ischemia is more deleterious than complete ischemia. The persistence of some circulation in the former situation may a) allow oxidative reactions to continue at a slow rate b) lead to excessive tissue lactic acidosis by continued supply of substrate for anaerobic glycolysis. Our studies concerning brain tissue concentrations of reduced and oxidized glutathione, fatty acids and phospholipids in reversible, pronounced, incomplete and complete ischemia fail to support the hypothesis that oxidative damage is an important factor for the development of irreversible neuronal damage. On the other hand, our studies have shown that the degree to which lactate accumulates during ischemia is critical for restitution.

Aerobiosis↗
PubMed1980

Magnetizable solid-phase fluoroimmunoassay of phenytoin in disposable test tubes.

We developed a fluoroimmunoassay for phenytoin in serum or plasma, based on the magnetic separation technique. The method involves sheep anti-phenytoin serum coupled to magnetizable cellulose/iron oxide particles, with a fluorescein-labeled phenytoin analog as tracer. After magnetic sedimentation of the solid phase from assay mixtures, the free fraction of the tracer is aspirated, removing endogenous fluorophores and other interfering components of the sample. The antibody-bound tracer is then eluted from the solid phase into a methanolic buffer medium and quantitated fluorometrically. The entire procedure, including fluorometry, is performed within disposable polystyrene test tubes. The assay involves only simple reagents and equipment, and correlates closely with established radioimmunoassay (r = 0.97) and gas-liquid chromatographic (r = 0.98) techniques.

Animals↗
PubMed1980

Magnetizable solid-phase fluoroimmunoassay of thyroxine by a sequential addition technique.

We describe a simple fluoroimmunoassay for the determination of thyroxine concentrations in serum. The method, "sequential addition, separation fluoroimmunoassay," involves both thyroxine labeled with fluorescein and magnetizable cellulose/iron oxide particles to which antibodies to thyroxine have been covalently linked. Serum sample or standard is incubated with an excess of the solid-phase antibody; the particles, which now carry most of the antigen in the sample, are sedimented onto a magnet and the supernate, which contains endogenous fluorophores and other interfering factors, is removed and discarded. Excess labeled thyroxine is then added, and, after incubation, the fluorescence in the supernate (free fraction), which is related directly to the amount of thyroxine in the sample is measured. For the whole procedure, including fluorometry, each sample is treated entirely within disposable polystyrene test tubes. Correlation studies with two different radioimmunoassays showed good agreement.

Fluoresceins↗
PubMed1979

Use of antibodies against the label in non-separation non-isotopic immunoassay: 'indirect quenching' fluoroimmunoassay of proteins.

Antibodies against the label are introduced as a potentially useful reagent in nonisotopic immunoassay. They may permit end point determination without the need for a separation step, provided (i) that steric hindrance selectively prevents their binding to the antibody-bound fraction of the labelled antigen in an immunoassay mixture, and (ii) that their binding to the label in the free fraction results in a change in its signal. This 'indirect' approach was investigated in systems employing the fluorescein label and antibodies to fluorescein which quenched the fluorescence of free labelled antigen. 'Indirect quenching' fluoroimmunoassays for human serum albumin, human immunoglobulin G and human placental lactogen were demonstrated. These assays for proteins may be contrasted with conventional non-separation techniques, which are usually best suited to the determination of haptens.

Animals↗
PubMed1979

The organization and isolating function of insect rectal sheath cells: a freeze-fracture study.

In termites and roaches the well-defined rectal papillae each comprise a layer of columnar principal cells specialized for active transport and a layer of basal cells. The whole cell group is entirely surrounded by several series of flattened 'sheath cells' (formerly termed 'junctional cells') which abut onto the basal components of the papilla. The sheath cells secrete a specialized sclerified cuticle which forms the framework of the papilla. Their regularly pleated apical membrane is closely apposed to the cuticle and contains parallel and closely spaced rows of intramembranous particles. at this level, no subcuticular space is present and hence the space associated with the apical surface of the principal cells is defined as an isolated compartment. Typical septate junctions are present between the sheath and basal cells; however those linking adjacent sheath cells are structurally unusual: they extend to the basal surface rather than being restricted to the apical zone, are frequently interrupted and in replicas are represented by relatively short and irregularly oriented particle rows. Moreover, lateral sheath cell contacts display two further peculiarities: absence of an apical desmosomal ring and paucity of gap junctions. Structural observations suggest that the sheath cells isolate the principal cells from communication with the hemolymph, consequently enhancing their efficiency in water and ionic regulation. Comparable cells have been described in a number of insects, but the 'isolation' system presents varying degrees of complexity, for which an evolutionary scheme is proposed.

Animals↗