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Biomedical subjects

C H Smith

Publications and source records attributed to C H Smith.

At least 163 records · Page 9Linked to original sources
PubMed1983

Anterior ischaemic optic neuropathy: recurrent episodes in the same eye.

Anterior ischaemic optic neuropathy is characterised by a sudden, painless loss of vision, optic disc oedema, and nerve fibre bundle visual field defects. It may be associated with giant cell arteritis but is usually idiopathic. Although subsequent involvement of the second eye is common, more than one episode in the same eye is extremely rare. Four patients with recurrent anterior ischaemic optic neuropathy in the same eye are described.

Edema↗
PubMed1983

Functional disease in neuro-ophthalmology.

Techniques for assessment of the functional basis for neuro-ophthalmic complaints are given. By use of these techniques, most neurologists will discover that the majority of patients will resolve their symptoms without unwarranted medical procedures.

Adult↗
PubMed1983

The neuro-ophthalmic examination.

A properly performed history and examination are essential to diagnosing correctly neuro-ophthalmic disorders. Aspects of the neuro-ophthalmic history and examination, particularly those dealing with evaluation of visual loss, are reviewed.

Color Perception Tests↗
PubMed1983

Folacin content of tea.

Total folacin and free folacin activities of 22 commercial tea samples, involving 5 types and 14 brands, were determined by a microbiological assay, using Lactobacillus casei (ATCC 7469). Substantially higher amounts of folacin were found in tea leaves than had been reported previously, due to an improved assay method with added ascorbic acid to protect the labile folate forms. Tea brews made from green and black teas contained approximately three to four times more folacin than the brews made from oolong tea, herb tea, and instant tea powders. Tea brews made from loose leaf teas and tea bags did not differ appreciably in folacin content. However, the tea bag itself inhibited folacin extraction. A range of 3% to 25% of the RDA for folacin can be met by consuming five servings (5 to 6 oz. per serving) of tea daily.

Folic Acid↗
PubMed1983

The Kodak Ektachem 400 Analyzer evaluated for automated enzymic determination of plasma creatinine.

We have evaluated an automated creatinine iminohydrolase procedure for plasma creatinine analysis, as used in the Kodak Ektachem 400 Analyzer. The correlation with kinetic and end-point (equilibrium) alkaline picrate procedures is generally excellent. The enzymatic procedure has the advantage of being unaffected by bilirubin, cephalosporins, and acetoacetate, all of which interfere in alkaline picrate procedures. Its accuracy, however, greatly depends on calibration values provided by the manufacturer. Storage of samples at -20 degrees C produced little change in measured creatinine. The Ektachem procedure has a greater range of linearity (140 mg/L) than the alkaline picrate procedures, but it shares with them the disadvantages of suboptimal precision in the normal range. The increased specificity, ease of performance, and other advantages of this use of creatinine iminohydrolase make it an attractive procedure.

Adult↗
PubMed1983

Interference by hemolysis with various methods for total calcium and its correction by trichloroacetic acid precipitation.

We evaluated the influence of hemolysis on total serum calcium as determined with the Du Pont aca, SMA 12/60, Ektachem 400, Corning 940 EGTA titrator, and the Beckman Astra 8, comparing results with those obtained by atomic absorption spectroscopy. We find that hemoglobin does not influence calcium measurements with the SMA 12/60, Ektachem 400, or Beckman Astra 8. The presence of hemoglobin exceeding 2 to 3 g/L caused falsely high results with the aca and falsely low results with the Corning 940 titrator. Similar interferences may be observed with other titrating or colorimetric procedures that involve direct reaction of the sample with o-cresolphthalein complexone or calcein. Upon removal of the hemoglobin by precipitation with trichloroacetic acid, the values obtained with the aca and the Corning 940 EGTA titrator were similar to those measured by atomic absorption. With nonhemolyzed serum samples the acid treatment had little or no effect on the aca procedure but resulted in a positive bias of approximately 10% with the EGTA procedure. Thus we recommend this trichloroacetic acid procedure for measuring calcium in hemolyzed samples with the aca and, with certain reservations, with the EGTA titrator.

Autoanalysis↗
PubMed1982

Plaque causing homonymous hemianopsia in multiple sclerosis identified by computed tomography.

Three patients with multiple sclerosis (women 20, 24, and 30 years old) had demyelinative plaques that produced homonymous hemianopsia. These lesions were identified by computed tomography which showed the plaques as hypodense areas. All patients with homonymous hemianopsia should undergo computed tomography; if a hypodense or enhancing lesion is identified, the diagnosis of multiple sclerosis must be considered.

Adult↗
PubMed1982

Placental amino acid uptake. VI. Regulation by intracellular substrate.

Amino acid uptake by human placental tissue is regulated by intracellular amino acids. alpha-Aminoisobutyric acid (AIB) uptake was reduced at intracellular AIB concentrations of 0.8 mM. The magnitude of reduction increased sharply between 1 and 3 mM and reached a maximum of 45% at 5 mM. Suppression was specific to the "A" system. It occurred only when both the amino acid used for preloading and that used as an uptake substrate were active with that system. In the "L" system, facilitation apparently occurs, and in the "ASC" system there is no apparent effect. The system specificity as well as other evidence indicated that suppression is caused by substrate present intracellularly rather than by dilution of extracellular substrate. Suppression was independent of inhibitors of protein synthesis and was not seen in membrane vesicles prepared from preloaded tissue, indicating that intracellular substrate interacts directly with the carrier (transinhibition) rather than altering its synthesis or degradation. The A system transinhibition has the potential to regulate syncytial uptake in vivo and limit variation due to changes in maternal plasma amino acid concentration.

Amino Acids↗
PubMed1980

Placental amino acid uptake. V. Relationship to placental maturation in the rat.

The functional maturation of the placenta during the latter portion of pregnancy is almost certainly essential to fetal growth but its mechanism is largely unknown. To determine the role of changes in intrinsic cellular transport in this process we measured the activity of transport systems for AIB between day 14 and term, a period of known marked increase in in vivo AIB transfer in the rat. In vitro incubation demonstrated that the labyrinthine tissue possessed two transport systems for cellular AIB uptake. Their maximum velocities remained essentially constant from day 16 to term and the intracellular concentration achieved during incubation actually decreased with gestational and the intracellular concentration achieved during incubation actually decreased with gestational age. In vitro tissue preincubation increased cellular uptake of AIB and this response also decreased with maturation. Thus changes in intrinsic transport mechanisms do not at all parallel the very large maturational increase in in utero amino acid transfer. Changes in intrauterine factors such as blood flow, the hormonal millieu, or fetal utilization and the resultant placental-fetal concentration gradients are much more likely to account for the increase in transfer than are alterations in cellular transport mechanisms.

Amino Acids↗
PubMed1980

Adaptation of the EMIT theophylline assay to kinetic analyzers: the relationship of reaction kinetics to calculation procedures.

We investigated the kinetic characteristics of an enzyme immunoassay system (EMIT) for the determination of theophylline. Less than 10% of the glucose-6-phosphate and NAD+ are consumed and the glucose-6-P-dehydrogenase-theophylline complex is essentially saturated with these substrates during the course of the reaction. However, apparently as the result of antibody heterogeneity, the rate does change during the course of the reaction. As a result, the values of the kinetic parameters for the theophylline saturation curve vary with the timing interval chosen for measurement. We show that the values of these parameters govern the application of the available methods of calculating EMIT data, the graphical procedure suggested by the manufacturer, logit-log, log-log, and curve fitting. These studies (1) explain the basis of the graphical procedure and why it does not always provide proper calibration, (2) show that to appropriately understand the application of any of the calculation procedures one should determine the values of the kinetic constants of the theophylline saturation curve in the particular assay conditions, and (3) illustrate simple, practical procedures for determining the values of these constants for any instrument-EMIT assay system. Specific illustrations are shown for the EMIT theophylline system with two kinetic analyzers, the Abbott ABA-100 and Gilford 3500, with which markedly different reaction conditions are used.

Autoanalysis↗
PubMed1980

A clinically applicable high-pressure liquid chromatographic method for measurement of serum theophylline, with detailed evaluation of interferences.

A high-pressure liquid chromatographic method for the routine measurement of serum theophylline that is accurate, specific, and sensitive is presented. It is technically simple, requires only 50 microliter serum, and takes relatively little technician time. Values for theophylline in sera obtained by this method correlate well with those obtained by use of a gas-liquid chromatographic method (r = 0.980) and with values obtained by the commonly used spectrophotometric method (r = 0.939) when the latter is free of interference. The assay has been employed for two years in a routine clinical chemistry laboratory, with interassay coefficients of variation of 2.4-3.2%. Interferences have been identified at an incidence rate of 3.8% of all specimens, and interfering substances include cephazolin, chloramphenicol, sulfamethoxazole, and sulfisoxazole. A calculation technic that allows a reliable and clinically useful estimation of a range of concentrations of theophylline in the serum when these interferences are present is described. In contrast, the incidence of interferences with the spectrophotometric method is 4.9%, and in this method the interferences prevent the analysis of theophylline. Of 33 samples having interferences by use of the spectrophotometric method, the high-pressure liquid chromatographic technic yielded precise values for theophylline in 21 and reliable estimates of ranges of concentrations of theophylline in the remaining 12.

Cefazolin↗
PubMed1980

Emit assays for five major anticonvulsant drugs. An evaluation of adaptations to two discrete kinetic analyzers.

Because of the complex reaction kinetics observed with the enzyme multiplied immunoassay technic (EMIT), each adaptation of these assays must be specifically evaluated. Evaluations were done of the totally automated adaptations of these immunoassays for diphenylhydantoin, phenobarbital, primidone, carbamazepine, and ethosuximide to two kinetic analyzers that use markedly different reaction conditions, the Gilford System 3500 and the Abbott Bichromatic Analyzer-100. Comparisons of data from EMIT assays on the Gilford 3500 with data from EMIT assays on the ABA-100 and with data from gas-liquid chromatographic analyses for the five anticonvulsant drugs showed good correlations (r greater than or equal to 0.96) and little or no additive or proportional biases, as determined by joint confidence intervals. Between-run precision for each EMIT anticonvulsant drug assay on both analyzers was less than 6%, better than that obtained with gas chromatography. No interference by more than 40 different drugs, by hemoglobin (6 g/l), or by bilirubin (200 mg/l), and no or minimal cross-reactivity with any of the five EMIT anticonvulsant drug assays on either analyzer were found.

Anticonvulsants↗
PubMed1980

Interrelationship of dietary ascorbic acid and iron on the tissue distribution of ascorbic acid, iron and copper in female guinea pigs.

Female guinea pigs were fed diets varied in ascorbic acid and iron concentration for 21 days. Tissue concentrations of ascorbic acid, iron (total, ferritin and hemosiderin) and copper were determined in blood, liver and spleen. High dietary ascorbic acid (10 times control) increased tissue ascorbic acid levels and produced a decrease in liver ferritin and hemosiderin, without altering liver or plasma total iron. Conversely, splenic total iron increased with no changes in ferritin and hemosiderin iron. The increased ascorbic acid did lower copper levels in blood and liver, 39% and 52%, respectively. In guinea pigs maintained on an ascorbic acid-free diet for 21 days, a decrease in hepatic ferritin and total iron was observed, as well as an increase in splenic hemosiderin and total iron. No change in plasma iron was observed nor were any of the copper pools altered. Intake of high dietary iron (10 times control) increased hepatic iron stores and produced a reciprocal decrease in hepatic copper. Even though splenic iron increased, no significant change in copper resulted. The significance of these nutrient interactions is discussed.

Animals↗
PubMed1980

Monosaccharide transport across microvillous membrane of human placenta.

Transport through the microvillous membrane of the syncytium is the first step in placental transfer of nutrients. We have therefore studied glucose transport by isolated microvillous membrane vesicles. Transport occurred by selective and rapid facilitated diffusion, which was inhibited by phloridzin, phloretin, cytochalasin B, and HgCl2. Nonmediated diffusion of the substrate was found by three independent methods to be very slow. Competition studies showed that aldohexoses in the C-1 chair conformation were the preferred substrates. Transport was independent of sodium gradients and was not modulated by insulin. However, several steroids inhibited transport including estriol and progesterone, which are abundant in utero. Kinetic analysis by equilibrium exchange demonstrated a Km of 31 mM and a Vmax of 120 nmol . s-1 . mg protein-1. The Km and Vmax suggest a large capacity in relation to calculated fetal needs. In consequence of this capacity, intrasyncytial concentrations of glucose are probably maintained near those of maternal blood. Augmentation of transport at this membrane by hormones or other agents is unlikely to increase fetal supply of glucose, but down regulation by steroids may serve a regulatory function.

Biological Transport↗