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Biomedical subjects

G J Walker

Publications and source records attributed to G J Walker.

At least 73 records · Page 4Linked to original sources
PubMed1986

Determinants of the utilization of maternal and child health services in Jordan.

The utilization of antenatal, delivery and postnatal services by a random sample of married women in Jordan during their most recent pregnancy resulting in a live birth is analysed. Marked variations are shown in the use of these services and of preventive infant care for women living in urban and rural areas. Women with increasing levels of formal education and those living near services were significantly more likely to use services. If effective coverage of these services is to be achieved then it is suggested that greater emphasis should be placed upon outreach and realistic social marketing.

Adolescent↗
PubMed1985

Synthesis, formulation, and clinical pharmacological evaluation of hydralazine pyruvic acid hydrazone in two healthy volunteers.

Hydralazine pyruvic acid hydrazone [2-(phthalazin-1-yl hydrazono)propionic acid; 1] is a major plasma metabolite of hydralazine in humans. A number of in vitro and animal studies have suggested that this hydrazone may have cardiovascular activity and could account for the prolonged antihypertensive effect of hydralazine in humans in the absence of detectable plasma levels of the parent drug. To study this possibility, the soluble sodium salt of hydralazine pyruvic acid hydrazone (2) was synthesized, its chemical purity and stability was checked, and an intravenous formulation was prepared. Isomeric forms were identified. Doses of 0.3, 0.6, and 1.1 mumol/kg of 2 were administered intravenously to one slow and one heterozygous fast acetylator of sulfamethazine. The slow acetylator received two additional doses of 0.06 and 0.14 mumol/kg. Peak plasma levels of 1 of 18 mumol/L were attained without tachycardia or hypotension in either subject. There was no evidence of nonlinearity in kinetics over the dose range studied and clearance remained constant in both subjects (0.517 +/- 0.033 mL/min/kg in the slow acetylator and 0.744 +/- 0.058 mL/min/kg in the fast acetylator). The distribution of 1 varied unpredictably with dose, and changes were reflected in the terminal half-life (3.47-5.97 h in the slow acetylator and 2.06-5.33 h in the fast acetylator). Only traces of the acetylated metabolite of hydralazine, 3-methyl-s-triazolo[3,4-a]phthalazine (3), were detected in the plasma of the subjects, suggesting that significant metabolism via this route was unlikely. An established and specific assay for hydralazine was further modified to allow measurement of levels as low as 1 nmol/L (0.2 ng/mL).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylation↗
PubMed1985

Inducible and constitutive formation of fructanase in batch and continuous cultures of Streptococcus mutans.

The production of extracellular beta-D-fructanase by several strains of Streptococcus mutans was studied in continuous culture. When glucose was the limiting nutrient, S. mutans K1-R and OMZ176 accumulated fructanase to maximum levels at low growth rates (dilution rate 0.05-0.10 h-1), due to the longer residence times of the bacteria in the culture vessel under these conditions. Extracellular fructanase activity was greater than has been previously reported for batch cultures. The rate of fructanase production for both S. mutans strains K1-R and OMZ176 increased with increasing growth rate when glucose was limiting. Under conditions of glucose sufficiency, the rate of fructanase production was always lower than in cultures where glucose was limiting, irrespective of the growth rate. Cultures of S. mutans Ingbritt (serotype c) grown with sorbitol- or glucose-limitation synthesized fructanase at a very low basal rate. When fructose was the limiting carbohydrate the enzyme was induced with a maximum rate of production occurring at a dilution rate of 0.40 h-1. Strains of S. mutans from other serotypes (a, d, d/g) were either not affected by changing the limiting sugar from glucose to fructose or else fructanase activity was slightly decreased in the fructose-limited medium. Fructanases from various strains of S. mutans readily hydrolysed (2----6)-beta-D-fructans, but all possessed the ability to hydrolyse (2----1)-beta-D-fructans to varying degrees.

Bacterial Proteins↗
PubMed1984

Activity of Streptococcus mutans alpha-D-glucosyltransferases released under various growth conditions.

The effect of a variety of growth conditions on extracellular D-glucosyltransferase (GTF) activity of Streptococcus mutans strains in continuous culture has been studied. Maximum GTF activity was found at low growth rates and at pH 6.5, and under this condition the predominant glucosyltransferase was GTF-S, an enzyme that synthesized soluble dextran. At high growth rates, the proportion of GTF-S decreased, and 50% or more of the total glucosyltransferase was GTF-I, an enzyme that synthesized water-insoluble (1 leads to 3)-alpha-D-glucan. Variation in the relative activities of GTF-S and GTF-I results in such diversity in the glucans synthesized from sucrose that it is virtually meaningless to describe a structural analysis of S. mutans glucan without specifying the conditions of growth of the organism.

Culture Media↗
PubMed1983

Activity of fructanase in batch cultures of oral streptococci.

Several strains of oral streptococci produced fructanase when grown in the absence of D-fructan in a complex medium supplemented with D-glucose. The major part of the activity was extracellular, and only 1-5% was associated with the cells. Release of fructanase began early in the exponential phase and the enzyme was stable in the stationary phase for several h if the pH did not fall below 6. Among the strains of Streptococcus mutans, serotypes a, d, and g released the highest amount of fructanase, and the low level of enzyme produced by strains of serotype c was increased when D-fructose replaced D-glucose as carbon source for growth. Fructanase of S. mutans readily hydrolysed (2 leads to 6)-beta-D-fructans, but (2 leads to 1)-beta-D-fructans and inulin were more resistant. Adsorption of fructanase to (2 leads to 6)-beta-D-fructan, or inhibition with Tris buffer, provided effective means of eliminating fructanase activity from culture filtrates. This procedure should permit a more accurate determination of fructosyltransferase activity of S. mutans strains.

Bacterial Proteins↗
PubMed1983

Inhibition by acarbose, nojirimycin and 1-deoxynojirimycin of glucosyltransferase produced by oral streptococci.

Acarbose is known to inhibit glucoamylase, maltase and sucrase. Our aim was to test whether it would also inhibit glucosyltransferase (GTF), to determine the type of inhibition and to compare the inhibitor potency of acarbose with that of nojirimycin and deoxynojirimycin, two other glucosidase inhibitors. Enzyme inhibition was measured either by chemical assay or by incorporation of radioactivity into product. Acarbose effectively inhibited the synthesis of polysaccharide by GTF from strains of Streptococcus mutans and Streptococcus sanguis, but not by fructosyltransferase from Streptococcus salivarius. Acarbose and 1-deoxynojirimycin were more potent inhibitors of GTF than maltose, nojirimycin or various amino sugars. The mechanism of action of these compounds is consistent with competitive inhibition.

1-Deoxynojirimycin↗
PubMed1983

Medical care in developing countries. Assessment and assurance of quality.

In recent years attention in developing countries has concentrated upon strategies to improve the equitable provision of essential health care--the primary health care approach. Very little work has been reported in connection with the quality of medical care, and yet for the successful outcome of care it is necessary that adequate health care processes be carried out. Conceptual, methodological, data, and organizational issues related to quality assessment and assurance are presented. The few examples of reported work concerned with these important aspects of medical care in developing countries are reviewed. Suggestions are made as to how measures to ensure reasonable quality might be further developed and refined.

Developing Countries↗
PubMed1982

Mortality rates and neonatal intensive care for very small babies.

Mortality rates of very small babies (those weighing 1500 g or less) born to mothers normally resident in the 11 health districts of the London portion of the North-east Thames Health Region in 1971-73 and 1975-77 were compared with admission rates to neonatal intensive care units in 1972 and 1976 in the region. There was no significant correlation between mortality and admission rates for babies weighing 1000 g or less during either period. For babies born weighing between 1001 and 1500 g this was also so in 1972. In 1976 however, mortality rates were significantly correlated negatively at 24 hours but not at 28 days with admission rates to neonatal intensive care.

Critical Care↗
PubMed1981

Metabolism of the polysaccharides of human dental plaque: release of dextranase in batch cultures of Streptococcus mutans.

Dextranase activity was determined in cell extracts and cell-free filtrates of Streptococcus mutans strains which had been grown in batch culture. Exo-dextranase activity was located chiefly in cell extracts, whereas endo-dextranase was mainly extracellular. Release of endo-dextranase began early in the exponential phase of growth, and ended when the concentration of residual sugar was low. Thus, dextranase expression was associated with rapidly growing cells, the yield of dextranase was increased several fold when the initial concentration of D-glucose in the medium was changed from 0.5% to 2%. The endo-dextranase was not stable at pH 5, and control of the pH of the culture was essential to preserve active dextranase during overnight growth. Strain Ingbritt (serotype c) and serotype d strains were the best dextranase producers; other strains (serotypes a, b, c, e and f) displayed much lower activity. The ability to produce endo-dextranase, and to synthesize alpha-D-glucans with a high proportion of (1 leads to 3)-linked sequences, appeared to be related properties. The possibility is discussed that the release of two enzymes, namely endo-dextranase and the D-glucosyltransferase (GTF-I) that synthesizes (1 leads to 3)-alpha-D-glucan, are factors that contribute to the cariogenicity of S. mutans serotype d.

Culture Media↗
PubMed1977

Metabolism of the polysaccharides of human dental plaque. Part II. Purification and properties of Cladosporium resinae (1 leads to 3)-alpha-D-glucanase, and the enzymic hydrolysis of glucans synthesised by extracellular D-glucosyltransferases of oral streptococci.

Cladosporium resinae (1 leads to 3)-alpha-D-glucanase has been characterized as an endoglucanase capable of completely hydrolysing insoluble (1 leads to 3)-alpha-D-glucans isolated from fungal cell-walls. D-Glucose was the major product, but a small amount of nigerose was also produced. The enzyme was specific for the hydrolysis of (1 leads to 3) bonds that occur in sequence, and nigerotetraose was the smallest substrate that was rapidly attacked. Isolated (1 leads to 3)-alpha-D-glucosidic linkages that occur in mycodextran, isolichein, dextrans, and oligosaccharides derived from dextran were not hydrolysed. Insoluble glucan synthesised from sucrose by culture filtrates of Streptococcus spp. were all hydrolysed to various limits; the range was 11-61%. A soluble glucan, synthesised by an extracellular D-glucosyltransferase of S. mutans OMZ176, was not a substrate, whereas insoluble glucans synthesised by a different D-glucosyltransferase, isolated from S. mutans strains OMZ176 and K1-R, were extensively hydrolysed (84 and 92%, respectively). It is suggested that dextranase-CB, a bacterial endo(1 leads to 6)-alpha-D-glucanase that does not release D-glucose from any substrate, could be used together with C. resinae (1 leads to 3)-alpha-D-glucanase to determine the relative proportions of (1 leads to 6)-linked to (1 leads to 3)-linked sequences of D-glucose residues in the insoluble glucans produce by oral streptococci. The simultaneous action of the two D-glucanoses was highly effective in solubilizing the glucans.

Cladosporium↗