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Biomedical subjects

L S de Villiers

Publications and source records attributed to L S de Villiers.

At least 19 recordsLinked to original sources
PubMed1992

Family history as a risk factor for coronary heart disease in South African families.

This article presents data on, and applies a procedure for the statistical quantification of, family history as a risk factor for coronary heart disease (CHD) in three sub-samples (groups) of families: I--a healthy control group; II--families with familial hypercholesterolaemia (FH); and III--families identified by an index case with CHD. With regard to the average family history of CHD (calculated as an index for each family, and as a mean index for each group), group II differs significantly from group I and marginally significantly from group III; family groups I and III do not differ from each other statistically. By means of significance tests developed for this purpose, the groups of families are shown to be significantly heterogeneous, by being composed of families highly resistant against and susceptible to CHD. This is illustrated for example in group II, where some FH families can be shown to be highly resistant to CHD, compared with other FH families with a very strong history of CHD. The exact number and proportion of such families at different levels of significance is calculated and the actual families with the highest and lowest calculated family indices, respectively, are then identified (illustrated by examples). The practical significance of the statistical procedure of quantifying and applying family history as a risk factor for CHD, is discussed in terms of epidemiological and preventive health considerations.

Adolescent↗
PubMed1989

Genetic polymorphism of glutamate-pyruvate transaminase (alanine aminotransaminase): influence on erythrocyte activity as a marker of vitamin B-6 nutritional status.

A new, sensitive, two-step method free from interference by hemoglobin that measures erythrocyte glutamate-pyruvate transaminase (E-GPT) activity is described. Several aspects of E-GPT activity as an index of vitamin B-6 nutritional status were investigated with this method. 1) GPT shows a structural genetic polymorphism with two common alleles resulting in three phenotypes. In a population study (n = 92) E-GPT activity differed significantly (p less than 0.001) among the three phenotypic groups. Plasma pyridoxal-5'-phosphate concentrations in the three groups did not differ significantly. Therefore, E-GPT activity can only be used to assess vitamin B-6 nutritional status if GPT phenotype is accounted for. 2) Pyridoxine supplementation (10 mg/d) significantly (p less than 0.0001) increased E-GPT activity and decreased (p less than 0.0001) the percentage stimulation by pyridoxal-5'-phosphate in vitro although the absolute amount of in vitro stimulation by pyridoxal-5'-phosphate changed only marginally. 3) Inorganic phosphate inhibits in vitro activation of E-GPT by pyridoxal-5'-phosphate.

Alanine Transaminase↗
PubMed1988

Aldosterone response to metoclopramide is mediated through the autonomic nervous system in man.

This study primarily examines the role of the autonomic nervous system in the aldosterone response to metoclopramide since there is conflicting evidence as to the involvement of a dopaminergic mechanism in this response. Six normal male volunteers in metabolic balance at 100 mmol sodium/day and 60 mmol potassium/day constant intake received metoclopramide, 10 mg i.v., on five different occasions. The dosing was either metoclopramide alone or combined with ganglionic, muscarinic, beta-adrenergic or calcium-channel blockade. Metoclopramide increased serum aldosterone significantly to 163.3% of basal level at 10 min. Atropine blunted this response and the 10 min level was significantly reduced to 116.03% of the basal value. The highest aldosterone levels were attained when metoclopramide was administered during a trimethaphan infusion and a peak of 292.8% of basal level occurred at 90 min. In the presence of atenolol, with or without nifedipine, the metoclopramide-induced aldosterone response was significantly greater at 15 min than with metoclopramide alone. The results of this investigation suggest that the aldosterone response to metoclopramide is mediated by acetylcholine released from post-ganglionic cholinergic nerve terminals, and that an adrenergic mechanism exerts a tonic inhibitory influence on aldosterone secretion in man.

Adult↗
PubMed1987

Effect of different levels of oral pyridoxine supplementation on plasma pyridoxal-5'-phosphate and pyridoxal levels and urinary vitamin B-6 excretion.

Plasma pyridoxal-5'-phosphate and pyridoxal levels increased significantly (p less than 0.05) when single, oral bolus doses of pyridoxine were increased from 10 to 25 and from 25 to 50 mg in nine female volunteers. However, when the dose was increased to 100 mg, plasma pyridoxal-5'-phosphate levels did not differ significantly from those recorded after the 50 mg dose. Within 3 h plasma pyridoxal levels rose with a factor of 3.85 compared with the 50 mg dose but high pyridoxal levels were eliminated from the circulation. Renal clearance of pyridoxal remained a constant, low percentage (less than 2.0%) of each pyridoxine supplement in spite of the observed very high circulating pyridoxal levels. Pyridoxine supplementation is discussed in relation to circulating pyridoxal-5'-phosphate and pyridoxal availability for cellular metabolism.

Administration, Oral↗
PubMed1985

Stability of pyridoxal-5-phosphate semicarbazone: applications in plasma vitamin B6 analysis and population surveys of vitamin B6 nutritional status.

The determination of pyridoxal-5-phosphate (PLP) and pyridoxal (PL) in plasma requires the availability of dark room facilities, due to the photosensitivity of these vitamin B6 vitamers. The fact that the semicarbazone forms of PL and PLP are more strongly fluorescent than the underivatized B6 vitamers has been exploited in plasma analyses, but it was not previously realised that these semicarbazone forms are also very stable even under conditions that lead to rapid decomposition of free PL and PLP. The stabilisation of PLP and PL obtained in this manner is sufficient and fully adequate to meet the practical requirements of clinical field studies. We report a high-performance liquid chromatographic method for plasma PLP and PL determinations based on precolumn semicarbazone formation and fluorescence detection. The method is sensitive enough for quantitative plasma PLP determinations even in B6-deficient patients.

Chromatography, High Pressure Liquid↗
PubMed1983

Further evidence on the effect of vitamin E on the cholesterol distribution in lipoproteins with special reference to HDL subfractions.

Earlier claims that oral administration of alpha-tocopherol results in significant and considerable increase in the serum total HDL concentration could not be substantiated. The present investigation does, however, show that lipoproteins are affected by alpha-tocopherol in other ways, the main effects being an increase in LDL-cholesterol and also in the HDL3-V cholesterol, an HDL3-subfraction determined by polyacrylamide gel electrophoresis. The established lipoprotein risk indices (LDL/HDL and HDL3/HDL2 ratios) were unfavorably affected as a result of alpha-tocopherol treatment. It is concluded that on the basis of available evidence, there is no reason to believe that alpha-tocopherol has a role to play in the prevention and treatment of atherosclerotic disease.

Adult↗