Biomedical subjects

J M Van Zyl

Publications and source records attributed to J M Van Zyl.

8 recordsLinked to original sources

PubMed1995

An evaluation of strategic and threshold control measures against the Karoo paralysis tick, Ixodes rubicundus (Acari: Ixodidae) in South Africa.

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.

Animals↗

PubMed1995

Preoperative nutritional status and prognostic nutritional index in patients with benign disease undergoing abdominal operations--Part I.

OBJECTIVE: The aim of the first part of this study was to detect the incidence of preoperative malnutrition of clinical importance in patients with benign disease. METHODS: The preoperative nutritional status of 52 consecutive adult patients undergoing abdominal operations for benign conditions was studied prospectively by objective and subjective nutritional criteria. The postoperative outcome was monitored until discharge or death. The preoperative nutritional status was correlated with the postoperative outcome. RESULTS: Protein energy malnutrition was identified in 20 (38%) of the 52 patients. Of these 20 malnourished patients, 15 (75%) developed complications after surgery, compared with 7 (22%) of the 32 well-nourished patients (p < 0.01). The most common abnormal values were serum transferrin concentration (n = 8), subscapula skinfold (n = 11), serum urea:serum creatinine ratio (n = 17), loss of appetite for more than 5 days (n = 24), and preoperative stay in hospital of longer than 5 days (n = 19). CONCLUSION: These results indicate that a combination of objective and subjective criteria may be important in the identification of clinical malnutrition.

Abdomen↗

PubMed1995

Preoperative nutritional status and prognostic nutritional index in patients with benign disease undergoing abdominal operations--Part II.

OBJECTIVES: Part II of this study was undertaken to develop a prognostic nutritional index for the identification of high risk patients with benign disease undergoing abdominal operations at the Universitas Hospital in Bloemfontein. METHODS: To accomplish this goal, 52 consecutive adult non-cancer surgical patients, admitted to the Universitas Hospital for a period of one year, were studied prospectively. The postoperative outcome was monitored until discharge or death. Various discriminant analyses were performed on the obtained data. Four prognostic indexes were compiled, including two nutritional and two mixed models. A short and medium length index were derived for both the nutritional and the mixed models. RESULTS/DISCUSSION: The results suggest that the short nutritional index may be the most practical for the prediction of surgical outcome in this specific set of patients. The short nutritional index included diet risk, serum albumin, body mass index, % ideal body weight, triceps skinfold and grip strength. It is further suggested that these indices be tested in another set of patients and be compared with other available prognostic models.

Abdomen↗

PubMed1994

Apparent hydroxyl radical generation without transition metal catalysis and tyrosine nitration during oxidation of the anti-tubercular drug, isonicotinic acid hydrazide.

Aromatic hydroxylation and formation of thiobarbituric acid-reactive substances occurred in a mixture of isonicotinic acid hydrazide (isoniazid) and catalase. Since these reactions were stimulated by phytic acid (a potent metal chelator), rather than inhibited, transition metal-catalysed hydroxyl radical generation was not implicated. Hydroxylation also occurred with isoniazid and phytic acid in the absence of catalase, albeit to a lesser extent. The independent effects of catalase and phytic acid are related to their abilities to catalyse isoniazid oxidation. In the presence of tyrosine, both the isoniazid/phytic acid system and authentic peroxynitrite generated dityrosine. Authentic peroxynitrite, as well as a phytic acid-mediated isoniazid oxidation product, have absorbance maxima at 302 nm. The yield of this isoniazid-derived product increased with pH and in the presence of a superoxide-generating system. A good correlation existed between absorbance at 302 nm and aromatic hydroxylation. Acid-induced decomposition of the 302 nm absorbance in the presence of superoxide dismutase led to the formation of a product absorbing in the same region as peroxynitrite-modified superoxide dismutase (350 nm at acid pH). Catalase catalysed peroxynitrite-mediated, as well as isoniazid/phytic acid-mediated tyrosine nitration, which was accompanied by Compound II formation (ferryl-catalase) in both cases. We postulate that peroxynitrite or a similar species is formed during isoniazid oxidation.

Catalase↗

PubMed1989

Stimulation of the chlorinating activity of human myeloperoxidase by thyroid hormones and analogues.

Thyroxine and triiodothyronine concentrations of 50 nM or lower can stimulate the chlorinating activity of the myeloperoxidase-H2O2-Cl- antimicrobial system in vitro. The initial rates of the chlorinating reaction with monochlorodimedone were similar for both thyroid hormones. Maximum stimulation occurred around pH 6 and a linear relationship exists between stimulation and thyroxine concentrations up to at least 1 microM. Of the various thyroxine analogues tested, stimulation was in the order: T4 (or T3) greater than triiodothyropropionic acid greater than 3,5-T2. Diiodotyrosine did not have any significant stimulatory effect. The oxidised product of the phenolic ring of T4, presumably a hydroxyquinone, may act as an additional electron carrier and thereby facilitates redox reactions.

Chlorides↗

PubMed1988

A computer program in compiled BASIC for the IBM personal computer to calculate the mean platelet survival time with the multiple-hit and weighted mean methods.

We developed an easy-to-operate computer program for the IBM personal computer to calculate, display and store in a database platelet kinetic data determined by analysis of the rate of clearance of radiolabeled blood platelets from the circulation. This was done by curve fitting using the weighted mean method and multiple-hit model. These models are complementary and calculating the mean platelet survival time with both is recommended. Improvement of the weighted mean method was investigated. The optimized weighting and fitting the exponential function with the Marquardt non-linear least squares method improved the weighted mean method. The weighted mean and multiple-hit models fit the survival curve data equally well. The calculation of the mean platelet survival time with the weighted mean method was very fast. The duration of calculation with the multiple-hit model could take up to 2 minutes. Calculation of the mean platelet survival time using both models has the advantage that conditions when calculation of the mean platelet survival time would be invalid, can be detected. The computer program will promote the valid comparison of results obtained at different institutions.

Blood Platelets↗

PubMed1988

The effect of thyroxine and related compounds on the aerobic myeloperoxidase--catalysed oxidation of NADH.

Thyroxine concentrations as low as 1 microM significantly stimulate compound III formation during aerobic oxidation of NADH by highly purified myeloperoxidase. This increased compound III formation is paralleled by an increased oxidation of NADH. Stimulation of various thyronine and tyrosine analogues was in the order T4 greater than T3 greater than 3,5-T2 (or triiodothyropropionic acid). Thyronine and diiodotyrosine had no significant effect. From the potencies of the various thyronines to stimulate compound III formation, the following structural features seem necessary: (1) Substitution of thyronine with four iodine atoms. (2) An amino group on the alanine side chain. (3) Both aromatic rings of thyronine.

Aerobiosis↗

PubMed1984

Solubilization of peroxidase from porcine thyroids and characterization by photoaffinity labelling.

Peroxidase was solubilized without proteolysis from porcine thyroid particulate fraction with the nonionic detergent, 1-O-n-octyl-beta-D-glucopyranoside. The enzyme was able to catalyze the oxidation of guaiacol and the iodination of bovine serum albumin (33 atoms of iodine per molecule protein). Binding studies performed with the partially purified enzyme indicated that the substrates thyroxine (T4) and tyrosine compete for the same binding site on the enzyme. Dissociation constants of 0.9 nM and 0.5 nM were found for T4 and tyrosine, respectively. After photoaffinity labelling with underivatized 125I-labelled T4, gel chromatography on Sephacryl S-1000 revealed a relative molecular weight of about 100 000 for the solubilized enzyme. The peroxidase activity and haem-absorbance peak coeluted from the Sephacryl S-1000 column. SDS-polyacrylamide gel electrophoresis under reducing conditions indicated two major radiolabelled polypeptides, Mr 83 000 and Mr 42 600, as well as a smaller peak at Mr 15 400. The 15 400 molecular weight species is probably not part of the peroxidase complex, since it could partially be removed by Sephadex G-25 prechromatography . Further analyses confirmed that the partially purified enzyme is a haemoprotein absorbing maximally at 412 nm. The Soret band is shifted to 423 nm by reducing agents and the haem-cyanide complex has a maximum absorbance at 416 nm.

Affinity Labels↗