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Biomedical subjects

G M van Kempen

Publications and source records attributed to G M van Kempen.

At least 19 recordsLinked to original sources
PubMed1990

Analysis of phenprocoumon and its hydroxylated and conjugated metabolites in human urine by high-performance liquid chromatography after solid-phase extraction.

The anticoagulant phenprocoumon is mainly metabolized in humans to hydroxylated metabolites and their glucuronides. A method is described for the determination of phenprocoumon, 4'-hydroxyphenprocoumon, 6-hydroxyphenprocoumon, 7-hydroxyphenprocoumon, and their glucuronide and sulphate conjugates in human urine. Reversed-phase high-performance liquid chromatography is performed after selective extraction with disposable quaternary amine columns of untreated, and beta-glucuronidase- or sulphatase-treated urine samples. Urinary excretion data are presented for total, glucuronidated, sulphated and free phenprocoumon, 4'-hydroxyphenprocoumon, 6-hydroxyphenprocoumon and 7-hydroxyphenprocoumon in twelve patients after an average daily dosage of 1.3-4.2 mg phenprocoumon.

Adult↗
PubMed1987

[Lithium].

Explore the source record for details and available documents.

Bipolar Disorder↗
PubMed1985

Assay of platelet monoamine oxidase in whole blood.

Monoamine oxidase (MAO; EC 1.4.3.4.) was measured in whole blood with kynuramine as the substrate. Optimal circumstances were determined. By use of selective inhibitors, gradient centrifugation, dilution of samples and removal of thrombocytes from whole blood it was shown that this assay of MAO in whole blood is in fact a determination of platelet MAO. No reversible endogenous inhibitors are present in the blood. Because preparation of platelet-rich plasma may lead to considerable losses of specific subpopulations with relatively low or high enzyme activities, the advantage of using whole blood is that the MAO activity is determined in the whole platelet population.

Blood Platelets↗
PubMed1983

The effects of valproic acid on liver function.

To study a possible enzyme-inducing potency of valproic acid (VPA) in children, serum gamma-glutamyltranspeptidase (GGT) activity in serum and D-glucaric acid (GLA) excretion in urine were measured in 32 epileptic children who were on sodium valproate monotherapy (29.6 +/- 10.3 mg/kg/day). VPA did not affect GGT activity, but it selectively enhanced GLA excretion. To approach this phenomenon experimentally an attempt was made to induce a similar effect in animals. In guinea pigs it was possible to provoke a VPA induced rise in GLA excretion. In addition, vacuolisation of the cytoplasm of the hepatic parenchymal cells was observed. The question of the possible relationship between VPA hepatotoxicity and stimulation of GLA excretion remains to be answered.

Animals↗
PubMed1982

Serum concentrations and enzyme induction in epileptic children treated with phenytoin and valproate.

In a group of 59 epileptic children treated with phenytoin (PHT) and valproate sodium (VPA), either alone or in combination, the following effects were studied: (1) the reciprocal effect on the serum levels of the two drugs, and (2) the enzyme-inducing effects of both drugs. VPA had no effect on PHT levels, but PHT significantly decreased VPA concentrations. PHT enhanced both gamma-glutamyltranspeptidase activity (gamma-GT) and D-glucaric acid excretion (GLA); these effects were potentiated by VPA. VPA alone did not affect gamma-GT, but significantly enhanced GLA.

Child↗
PubMed1978

Kinetics and mechanism of the rat brain phenol sulphotransferase reaction.

Some properties of rat brain phenol sulphotransferase were investigated in in vitro at pH7.4. The enzyme was purified 10-fold by chromatography on DEAE-Sephadex -50. It can be assayed with 4-hydroxy-3-methoxyphenylethylene glycol or 4-methylumbelliferone as the sulphate acceptor. The partially purified enzyme is stable for at least 1 week when stored at 4 degrees C. It is, however, additionally activated (10--20%) and stabilized by 1 mM-dithiothreitol. The activity of the enzyme does not depend on the addition of exogenous Mg2+. The pH optima for the sulphation of 4-hydroxy-3-methoxyphenylethylene glycol and 4-methylumbelliferone are 7.8 and 7.4 respectively. Substrate inhibition by the sulphate acceptor is apparent at concentrations over 0.05mM. Initial-velocity studies in the absence and presence of product and dead-end inhibitors suggested that the mechanism of the rat brain sulphotransferase reaction is sequential ordered Bi Bi with a dead-end complex of enzyme with adenosine 3',5'-biphosphate and sulphate acceptor. The sulphate donor adenosine 3'-phosphate 5'-sulphatophosphate is the first substrate that adds to the enzyme, and the sulphate acceptor is the second substrate. The dissociation constant for the complex of enzyme with sulphate donor is 21 micron. The sulphated substrate is the first product and adenosine 3',5'-biphosphate is the second product that leaves the enzyme.

Adenine Nucleotides↗