Biomedical subjects
J C Allen
Publications and source records attributed to J C Allen.
Analysis of glycosaminoglycans in urine by using acridine orange fluorescence.
The fluorescence technique described here utilizes the electrostatic interaction between the polyanionic sites of glycosaminoglycans and the cationic dye Acridine Orange to analyse urinary glycosaminoglycans from patients suffering from mucopolysaccharidoses. The basis of the titration is the decrease in the fluorescence of free Acridine Orange that occurs when it is bound to polyanions. The effect of the presence of possible interfering materials such as salt, proteins and trace materials in urine was evaluated. This fluorescence technique is technically simple.
Transient cerebral dysfunction following chemotherapy for osteogenic sarcoma.
An unusual neurological syndrome occurred in 4 of 158 patients treated for osteogenic sarcoma with combination chemotherapy. There was an abrupt onset of focal cerebral deficits approximately ten days after chemotherapy with vincristine and high-dose methotrexate plus citrovorum factor rescue. The syndrome was short lived and always occurred early in the course of treatment. Prolonged neurological deficits remained in 2 patients. When similar chemotherapy was reinstituted in the 4 patients, no further neurological complications ensued. Possible causes include a leukoencephalopathy related to methotrexate or an embolic cerebral vasculopathy related to necrotic tumor microemboli emanating from the lungs.
Leukoencephalopathy following high-dose intravenous methotrexate chemotherapy: quantitative assessment of white matter attenuation using computed tomography.
A clinical or subclinical leukoencephalopathy occurs in some children after treatment of acute lymphatic leukemia with prophylactic cranial radiation therapy and parenteral or intrathecal methotrexate. We have observed a similar clinical leukoencephalopathy in patients with bone tumors treated with intravenous high-dose methotrexate and citrovorum factor without cranial irradiation. CT scans of such patients may indicate decreased white matter attenuation, but visual appraisal of this phenomenon is occasionally misleading. A computerized method for analyzing white matter hypodensity by determining the mean attenuation coefficient for one or several contiguous CT slices has therefore been developed. Serial comparisons of this mean attenuation coefficient appear to be more reliable than simple visual appraisal.
Determination of ventricular volume following metrizamide CT ventriculography.
Volume averaging, relatively slight differences in the mean attenuation coefficients of CSF and white/grey matter, and the irregular contours of the human ventricular system have so far seriously limited the accuracy of CT estimation of ventricular volume. Taking advantage of the high attenuation of metrizamide-containing CSF, we have developed three methods for computing ventricular volume after metrizamide CT ventriculography; these methods depend upon computer analysis of X-ray absorption data obtained from contiguous CT brain slices. All three methods were validated by CT scanning a formalin-fixed cadaver brain containing an apoxy-resin cast of the ventricular system. Calculated ventricular volumes were compared with the actual measured volume of the ventricular cast.
Metrizamide washout as a measure of CSF bulk flow.
Metrizamide was injected into the ventricular system of three adults and five children with indwelling ventricular catheters and subcutaneous CSF reservoirs. A first-order rate constant, k, for metrizamide washout from one lateral ventricle was determined with reference to ventricular metrizamide concentration on serial (up to six) postinjection CT scans. Lateral ventricular volume, Vv, was estimated after metrizamide injection by a planimetric method and by partial volume analysis, an interactive computerized technique. The rate of lateral ventricular CSF formation, If, was calculated as k X Vv and ranged from 0.0622 to 0.103 ml/min. Precise measurements of lateral ventricular CSF bulk flow depend upon adequate mixing of the injected contrast material with ventricular CSF and accurate measurements of lateral ventricular volume.
Dislodgeable residues of parathion and carbophenothion in Florida citrus: a weather model.
Explore the source record for details and available documents.
The effects of cancer therapy on the nervous system.
Explore the source record for details and available documents.
Commercial PHA preparations contain different mitogenic components.
Three commercially available purified phytohaemagglutinin (PHA) preparations have been examined both chemically and biologically. Marked differences were observed in both composition and mitogenic effect on lymphocytes; the existence of at least two distinct mitogenic fractions in PHA was confirmed.
Septic choroiditis with serous detachment of the retina in dogs.
The present study describes a model of multifocal septic choroiditis with serous retinal detachment after intracarotid injection of Staphylococcus aureus or Streptococcus faecalis. The fundus lesions occurred mainly in the tapetal area and, on ophthalmoscopic examination, were more extensive after S. aureus than after S. faecalis injection. On histopathologic examination there were microabscesses in the inner choroid and subretinal space, disrupting the outer retina but sparing the inner retina.
Chemotherapy for primary brain tumors.
Explore the source record for details and available documents.
The influence of micelle formation on lipoxygenase kinetics.
The effects of a series of n-alcohols and n-carboxylic acids on lipoxygenase activity was studied. It was shown that to a large extent the effects of these compounds could be ascribed to physiochemical interaction with the substrate solution rather than a direct action on the enzyme itself. The effect of better substrate analogues such as stearate and oleate could also be ascribed to this effect. A type-2 lipoxygenase was found to have a very unusual velocity-substrate relationship which could be normalized by addition of calcium chloride in amounts stoichiometric with the substrate. An excess of calcium inhibited the enzyme. By comparison of results with linoleoyl sulphate/linoleoyl alcohol mixed micelles, an explanation for this unusual velocity-substrate activity is presented.
Identification of a thymic inhibitor ('chalone') of lymphocyte transformation as a spermine complex.
Explore the source record for details and available documents.
Eye findings in the 13 trisomy syndrome.
The gross and microscopic eye findings in the first historic case of the 13-trisomy syndrome included: severe microphthalmia, coloboma of the ciliary body, cataracts, detached retina, and retinal dysplasia.
Affinity chromatography of lipoxygenases.
A number of aminohexyl agarose derivatives of unsaturated fatty acids have been prepared and evaluated as materials for the affinity chromatography of soybean and pea lipoxygenases. A practical method for a one-stage purification of soybean lipoxygenase-1, with a purification factor of 16, is described, using either linolenate or docosa-4,7,10,13,16,19-hexaenoate as ligands. Results show that alleged competitive inhibitors do not cause sharp elution from the affinity column, and that there is an increasing specificity of binding and sharpness of elution as the proportion of unsaturation in the ligand is increased. These results are discussed in terms of the relative importance of the types of bonding involved in enzyme-substrate binding.
Dislodgeable residues of ethion in Florida citrus and relationships to weather variables.
Five different treatments of ethion on Valencia orange trees were compared for decay rates and for ethion monoxon and ethion dioxon production under different environmental conditions. The oxon metabolite levels observed were low and always below the residue level of ethion itself. There were no significant differences in the decay rates of ethion between treatments. A model of ethion decay utilizing environmental variables as a time base is presented. This model explains 94% of the variation observed in ethion decay during very wet and very dry periods in Florida. The application of these results and general experimental approach to worker safety reentry standards is discussed.
On the lack of inotropy of cardiac glycosides on skeletal muscle: a comparison of Na+, K+-ATPases from skeletal and cardiac muscle.
Explore the source record for details and available documents.
Blood, brain, and cerebrospinal fluid concentrations of several antibiotics in rabbits with intact and inflamed meninges.
Because cerebrospinal fluid (CSF) antibiotic levels fail to predict either clinical success or relapse in the treatment of bacterial meningitis, we examined simultaneous antibiotic concentrations in the blood, brain, and CSF of control rabbits and of animals with experimental pneumococcal meningitis. Cefamandole pharmacokinetics were analyzed in detail and compared with those of cephalothin, ampicillin, penicillin G, and tobramycin. After 4 h of continuous intravenous infusion, cefamandole reached concentrations in both brain and CSF in excess of the minimal bactericidal concentration for the test organism and compared favorably with ampicillin and penicillin in achieving bacteriological cure. Cephalothin levels in the central nervous system remained undetectable in both control and infected animals during this time. Tobramycin concentrations were measurable in the CSF, but not in brain tissue in association with an inflammatory stimulus.