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Biomedical subjects

A M Osman

Publications and source records attributed to A M Osman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Major tick-borne diseases of sheep and goats in the Sudan.

Tick-borne diseases of sheep and goats have not been thoroughly investigated in the Sudan. Heartwater, the most important of the group, was reported only in the early '60s and malignant theileriosis of sheep in the mid '80s. Other tick-borne diseases of sheep and goats like anaplasmosis, Q fever, Nairobi sheep disease and babesiosis are expected to be present although the vector which transmit Nairobi sheep disease, Rhipicephalus appendiculatus is confined to a very narrow stretch on the Southern border with Zaire, Uganda and Kenya.

Animals↗
PubMed1996

Microperoxidase/H2O2-catalyzed aromatic hydroxylation proceeds by a cytochrome-P-450-type oxygen-transfer reaction mechanism.

The mechanism of aromatic hydroxylation of aniline and phenol derivatives in a H2O2-driven microperoxidase-8(MP8)-catalyzed reaction was investigated. It was shown that the reaction was not inhibited by the addition of scavengers of superoxide anion or hydroxyl radicals, which demonstrates that the reaction mechanism differs from that of the aromatic hydroxylation catalyzed by a horseradish peroxidase/ dihydroxyfumarate system. Additional experiments with 18O-labelled H2 18O2 demonstrated that the oxygen incorporated into aniline to give 4-aminophenol originates from H2O2. Furthermore, it was found that the addition of ascorbic acid efficiently blocks all peroxidase-type reactions that can be catalyzed by the MP8/H2O2 system, but does not inhibit the aromatic hydroxylation of aniline and phenol derivatives. Together, these observations exclude reaction mechanisms for the aromatic hydroxylation that proceed through peroxidase-type mechanisms in which the oxygen incorporated into the substrate originates from O2 or H2O. The mechanism instead seems to proceed by an initial attack of the high-valent iron-oxo intermediate of MP8 on the pi-electrons of the aromatic ring of the substrate leading to product formation by a cytochrome-P-450-type of sigma-O-addition or oxygen-rebound mechanism. This implies that MP8, which has a histidyl and not a cysteinate fifth axial ligand, is able to react by a cytochrome-P-450-like oxygen-transfer reaction mechanism.

Aminophenols↗
PubMed1996

Effect of sub-lethal doses of albendazole on the fecundity of Dictyocaulus viviparus.

During an evaluation of the efficacy of prolonged low-dose albendazole therapy on nematode infections in calves, it was observed that a dose-rate of 2 mg kg-1 given daily for 10 days was highly effective at expelling Dictyocaulus viviparus, but smaller doses suppressed the faecal output of larvae without killing the lungworms. A more detailed study with four experimentally infected calves given 1 mg kg-1 day-1 for 10 days showed that faecal output of larvae ceased after six to eight days but resumed four to six days after the withdrawal of the drug. The albendazole-induced sterility was therefore reversible. A subsidiary study showed that the strain of parasite used was fully susceptible to albendazole.

Albendazole↗
PubMed1994

In vivo effect of sublethal concentrations of albendazole metabolites on the structure of the reproductive organs of Dictyocaulus viviparus.

Dictyocaulus viviparus were harvested from calves treated daily with albendazole at dose-rates sub-lethal to this parasite and from matched untreated calves. Male and female reproductive tracts from the worms were examined by light and transmission electron microscopy. A first description of the testis of this nematode is provided. Cell division in the germinal zone of both male and female worms was arrested by in vivo exposure to albendazole metabolites and the cytoplasmic threads connecting the germinal cells to the rachis disappeared. In male worms from treated calves, the rachis was absent from the growth zone and severe ultrastructural damage of spermatogonia, spermatocytes and spermatozoa was apparent. In female worms, the rachis remained intact in the growth zone, obvious abnormalities being confined to the germinal zone, where the cytoplasm of the oogonia was disrupted and few nuclei seen, and to the uteri and ovijector which contained only undifferentiated ova. The detrimental effects of albendazole metabolites on male and female worms were quickly reversed after withdrawal of medication.

Albendazole↗
PubMed1993

Looking for two targets at the same time: one search or two?

A considerable amount of evidence suggests that, under conditions of high discriminability, subjects are able to process multiple elements in a visual display simultaneously when searching for a single target among distractors. Relatively little emphasis, however has been placed on the question of whether subjects can search for and detect multiple targets simultaneously. This latter question is the focus of the present report. In two experiments, we compare performance in single-target and multiple-target detection tasks in order to investigate whether or not multiple targets can be detected simultaneously. In Experiment 1, subjects searched for one or two targets that were defined by color. In Experiment 2, subjects searched for a color and/or a letter target. When the two targets were presented in the same location (e.g., a red X when Target 1 was red and Target 2 was an X), they seemed to be detected simultaneously. Implications for object-based processing of visual information are discussed.

Adult↗
PubMed1992

Prevention of doxorubicin-induced myocardial and haematological toxicities in rats by the iron chelator desferrioxamine.

Biochemical and histopathological evaluations of the protective effects of the iron-chelator desferrioxamine against the cardiac and haematological toxicities of doxorubicin in normal rats were carried out. A single dose of doxorubicin (15 mg/kg, i.v.) caused myocardial damage that manifested biochemically as an elevation of serum cardiac enzyme [glutamic oxaloacetic transaminase (GOT), lactic dehydrogenase (LDH) and creatine phosphokinase (CPK)] and cardiac isoenzyme levels and histopathologically as a swelling and separation of cardiac muscle fibers. Doxorubicin caused severe leucopenia and decreases in red blood cell counts and haemoglobin concentrations at 72 h after its administration. Desferrioxamine treatment (250 mg/kg, i.p.) carried out 30 min before doxorubicin administration protected the heart and blood elements from the toxic effects of doxorubicin as indicated by the recovery of levels of cardiac enzymes and isoenzymes and of red blood cell counts to normal values and by the absence of significant myocardial lesions. The findings of this study suggest that desferrioxamine can potentially be used clinically to prevent doxorubicin-induced cardiac and haematological toxicities.

Animals↗
PubMed1990

Liver purine nucleoside phosphorylase in Camelus dromedarius: purification and properties.

1. Purine nucleoside phosphorylase (purine nucleoside:orthophosphate ribosyl transferase, EC 2.4.2.1) was purified to electrophoretic homogeneity from the liver of Camelus dromedarius. 2. The enzyme appears to be a dimer with a 44,000 subunit mol. wt and displays non-linear kinetics with concave downward curvature in double reciprocal plots with respect to both inosine and orthophosphate as variable substrates. 3. The effect of thiol compounds on the enzyme activity and of pH on kinetic parameters is reported.

Animals↗
PubMed1989

Lens aldo-keto reductase of Camelus dromedarius: purification and properties.

Aldo-keto reductase has been purified 13,000-fold from the lens of the camel (Camelus dromedarius) to a specific activity of 85 U/mg protein. The enzyme is a monomeric protein, exhibiting a Mr = 40,000 upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. Camel lens aldo-keto reductase shows a broad substrate specificity, which is strictly dependent on NADPH, and is insensitive to inhibition by Sorbinil and valproate. Aldoses with a carbon chain with more than four residues, as well as glucuronate, are not reduced by the enzyme. On the basis of substrate specificity and sensitivity to inhibition, camel lens aldo-keto reductase appears to be distinct from the so far described aldose, aldehyde and carbonyl reductases.

Alcohol Oxidoreductases↗
PubMed1989

Liver uricase in Camelus dromedarius: purification and properties.

1. Uricase (urate: oxygen oxidoreductase, EC 1.7.3.3) was purified 750-fold from the liver of Camelus dromedarius. 2. The enzyme is a tetramer with a Mr of 100,000, displays high specificity for uric acid with a Km of 12 microM and is inhibited by a selected number of purine derivatives carrying oxygen at the C2 position. 3. The effect of pH and the inhibition by thiol compounds and chelating agents on the enzyme activity is reported. 4. Some lines of evidence suggesting the possibility of interaction of camel liver uricase with oligonucleotides are presented.

Animals↗
PubMed1989

NADPH-dependent reduction of glyceraldehyde: a unusually high activity in the lens of the camel (Camelus dromedarius).

The enzymes of the polyol pathway, namely aldose reductase and sorbitol dehydrogenase, were measured in camel lens extracts. A NADPH-dependent glyceraldehyde and erythrose reductase activity 25 times higher than that of calf lens was observed in camel lens. A preliminary comparison between this enzyme activity present in the camel and aldose reductase of calf lens is reported.

Aldehyde Reductase↗
PubMed1988

Modern mental chronometry.

Mental chronometry, in which conclusions about human information processing are reached through measures of subjects' reaction time, has contributed substantially to studies of cognition and action. During the evolution of the chronometric paradigm, several key issues have emerged. The issues concern (a) the existence of separable processing stages, (b) the degree to which various stages of processing produce partial outputs before they are completed, and (c) the discrete versus continuous form of the outputs. To obtain added temporal resolution, new reaction-time procedures have been developed, including special response-priming and speed-accuracy decomposition techniques that focus on quantitative patterns of reaction-time distributions and error rates. The present article summarizes these developments, starting with a historical review of chronometric research and proceeding to a survey of recent empirical and theoretical innovations. We also discuss the relevance and potential future impact of complementary work by cognitive psychophysiologists on event-related brain potentials and other physiological variables.

Cognition↗
PubMed1987

Glucocorticoid effect on melphalan cytotoxicity, cell-cycle position, cell size, and [3H]uridine incorporation in one of three human melanoma cell lines.

Three human melanoma cell lines of known content of specific glucocorticoid-binding sites were studied for colony formation after a microM dose of glucocorticoid combined with melphalan. In one of the three cell lines, M-5A, subcloned from M-5 (formerly designated RPMI 8322), the effect of combined treatment was markedly increased compared to that of melphalan even if the glucocorticoid was applied for 1 h only, 10 h before the melphalan. Semilogarithmic dose-effect plots for a reduction of final plating efficiency by glucocorticoid were curvilinear, according to a receptor-mediated process. The effects of glucocorticoid, melphalan, and their combination were linearized by bilogarithmic median-effect plotting which allowed the quantitation of a synergism which was more marked in case of glucocorticoid pretreatment, for 1 or 24 h, than on simultaneous exposure. According to sequential DNA per cell cytophotometry, melphalan abolished in M-5A a glucocorticoid-induced arrest in the G1 phase of the cell cycle. The cytotoxic synergism correlated with an apparent stimulation by glucocorticoid of the rate of acid-insoluble incorporation of [3H]uridine and [14C]leucine and an increase in cell size and protein content in M-5A cells but not in the other two cell lines. The way in which glucocorticoids induce an enhanced susceptibility to melphalan is not clear. Our results appear compatible with a hypothesis that chromatin in a transcriptionally activated state is more vulnerable to cytotoxic attack by an alkylating agent than under average conditions.

Cell Cycle↗
PubMed1987

Purine salvage as metabolite and energy saving mechanism in Camelus dromedarius: the recovery of guanine.

The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu.

Animals↗
PubMed1987

Structure and process in semantic memory: new evidence based on speed-accuracy decomposition.

Reaction-time and accuracy data obtained from studies of sentence verification have not been rich enough to answer certain important theoretical questions about structures and processes in human semantic memory. However, a new technique called speed-accuracy decomposition (Meyer, Irwin, Osman, & Kounios, 1986) may help solve this problem. The technique allows intermediate products of sentence verification to be analyzed more precisely. Three experiments with speed-accuracy decomposition indicate that verification processes produce useful partial information before they are completed. Such information appears to accumulate continuously at a rate whose magnitude depends on the degree of relatedness between semantic categories. This outcome is consistent with continuous computational (e.g., semantic-feature comparison) models of semantic memory. An analysis of reaction-time minima suggests that a discrete all-or-none search process may also contribute at least occasionally to sentence verification. Further details regarding the nature of these processes and the memory structures on which they operate can be inferred from additional results obtained through speed-accuracy decomposition.

Humans↗
PubMed1986

Studies on purine turnover in the camel (Camelus dromedarius) and zebu (Bos indicus).

Significantly higher hypoxanthine over uric acid ratios were found in camel plasma and urine, with respect to those of zebu. Enzyme levels of purine catabolism were markedly lower in camel than in zebu liver. Oxidation of hypoxanthine appears to be the limiting step of purine metabolism in camel liver. Any hepatic hypoxanthine appears to be actively converted into IMP in camel liver, rather than oxidized to uric acid.

5'-Nucleotidase↗
PubMed1985

Glucocorticoid receptors and cell cycle progression in human melanoma cell lines.

Proliferation of six established human melanoma cell lines was inhibited after treatment for 1 h with a high dose of glucocorticoid. Four of the lines with the capacity of colony formation were used to quantify final plating efficiency. Specific glucocorticoid binding sites in these cell lines ranged from 51,000 to 170,000 sites per cell as measured with a whole-cell assay. Growth inhibition was completely reversible in one cell line, irreversible in another, and partially reversible in two lines. Receptor content per cell correlated with the reduction in final plating efficiency of glucocorticoid-treated cells, suggesting a receptor-mediated event. A more than 90% growth inhibition and a 40% reduction in cell survival in the most sensitive cell line, M-5A, was accompanied by a dual blockage in G1 and G2/M phase that lasted till at least 96 h after treatment with 2.5 microM dexamethasone for 1 h. Evidence is presented of a real arrest of M-5A cells in G1 phase and a markedly retarded progression through G2; the blockage of G1-S transition was immediate and complete. Accumulation of G1 cells was observed in two other cell lines but was inconsistent in the fourth line studied by flow cytometry; in none of the three cell lines was G2/M accumulation observed. Stimulated melanogenesis after glucocorticoid treatment of M-5A and NKI-26 cells suggested differentiation of the cells during glucocorticoid-induced arrest.

Binding Sites↗