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Biomedical subjects

H A Kuiper

Publications and source records attributed to H A Kuiper.

At least 37 records · Page 2Linked to original sources
PubMed1989

A study on the carcinogenicity of human diets in rats: the influence of heating and the addition of vegetables and fruit.

The influence of dietary factors such as total composition, thermal processing, and the addition of vegetables and fruit on the tumour rate in rats was studied in a long-term experiment. Groups of 50 male and 50 female Wistar rats were fed one of the following diets: a semi-synthetic animal diet (A, control); diet A to which vegetables and fruit were added (B); an uncooked human diet (meat, bread and eggs) supplemented with semi-synthetic compounds (C); diet C with fried or baked products (D); a complete human diet consisting of heated products, vegetables and fruit prepared according to mean consumption figures in The Netherlands (E). The animal diets (A and B) contained 26.0 energy (E)% protein, 21.6 E% fat, 52.4 E% carbohydrate and 10.7% (w/w) fibre. The human diets contained 13.2 E% protein, 40.6 E% fat, 46.2 E% carbohydrate and 5% (w/w) fibre. The rats were fed ad lib. for 142 wk. In males and females fed human diets (C, D or E) hepatocellular vacuolization was observed. Male rats (but not female) fed the human diet had a significantly (P less than 0.02) higher incidence of epithelial tumours than those fed the animal diet. This increase was mainly due to tumours of the pituitary and thyroid. Frying and baking of food products (diet D) and the addition of vegetables and fruit (diet E) induced minor differences in tumour rate, but they were not statistically significant.

Animals↗
PubMed1989

Determination of sulfadimethoxine, sulfamethoxazole, trimethoprim and their main metabolites in porcine plasma by column switching HPLC.

A HPLC method for the determination of sulfadimethoxine, sulfamethoxazole, trimethoprim and their main metabolites in porcine plasma is reported. The metabolites under investigation were the N4-acetyl sulfonamides and 3'- and 4'-demethyl trimethoprim. In order to obtain a sensitivity of 25-50 ng ml-1, the application of column switching HPLC was investigated. An on-line preconcentration of the drugs and metabolites was preceded by an off-line sample pre-treatment. Parent compounds and metabolites were separated by reversed-phase HPLC followed by UV-detection. The mean recoveries for 4'-demethyl trimethoprim were greater than 80% while the mean recoveries for the other compounds were greater than 90%. Application of the method for analysis of plasma samples obtained from pharmacokinetic studies is described.

Animals↗
PubMed1989

The use of porcine hepatocytes for biotransformation studies of veterinary drugs.

1. Cultures of porcine hepatocytes with high viability were isolated from a liver sample by a simple procedure. In ageing monolayer cultures the cytochrome P-450 content and 7-ethoxycoumarin-O-deethylase activity decreased gradually while glutathione levels increased. 2. The nitrofuran, furazolidone, was rapidly metabolized, partly resulting in the formation of 3-(4-cyano-2-oxobutylidene amino)-2-oxazolidone. 3. Acetylating and deacetylating activities towards sulphadimidine and its N4-acetyl metabolite were present in porcine hepatocytes. Relative and absolute levels of these activities varied in different batches of hepatocytes. 4. No differences were seen in a number of enzyme activities measured in cytosolic and microsomal fractions isolated from different lobes of one liver. Differences between livers from different animals were marked.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1988

The effect of dietary nitrite and nitrate on the metabolism of sulphadimidine administered orally to pigs.

The in vivo interaction of sulphadimidine (SDM) with nitrite and nitrate has been investigated in pigs. It was shown that the combined oral treatment with SDM and nitrite but not nitrate leads to the formation of a deaminated compound, which becomes the major metabolite in plasma soon after cessation of the treatment. The major in vitro reaction product, 1,3-di(4-[N(4,6-dimethyl-2-pyrimidinyl)]-sulphamoylphenyl)-triazen e, DDPSPT as has been reported previously, could not be detected in blood, urine or faeces of the exposed animals. No effect of nitrite or nitrate could be observed on the acetylation of SDM.

Administration, Oral↗
PubMed1987

In vitro formation of a triazene compound by reaction of sulphadimidine and nitrite.

The interaction between the veterinary drug sodium sulphadimidine and nitrite has been studied under acid conditions and the formation of 1,3-di-(4-[N-(4,6-dimethyl-2-pyrimidinyl)sulphamoylphenyl)triazene (DDPSPT) was demonstrated. This compound was not mutagenic when tested on Salmonella typhimurium and Drosophila melanogaster. In addition to the formation of DDPSPT, desaminosulphadimidine was identified as a minor reaction product.

Animals↗
PubMed1987

The elimination of furazolidone and its open-chain cyano-derivative from adult swine.

1. A sensitive method for the determination of 3-(4-cyano-2-oxobutylidene amino)-2-oxazolidone, the open-chain cyano-derivative of the veterinary drug furazolidone, in swine plasma and tissues is described. 2. After dosing adult swine orally with furazolidone (690 mg/animal per day) for 10 days no furazolidone was detected in liver, kidney and muscle (less than 2 ng/g). The half life of furazolidone as measured from the terminal phase of the plasma curves was 45 minutes. In urine, small amounts (less than 0.3% of total dose) of furazolidone were detected. 3. In contrast to other animals, 3-(4-cyano-2-oxobutylidene amino)-2-oxazolidone is a minor metabolite in swine with a plasma half life of 4 h. No cyano-derivative was detected in liver and kidney (less than 5 ng/g) 2 h after the last administration of furazolidone; 24 h after the last administration, the concentration in plasma was less than 2 ng/ml and in muscle less than 5/g. 4. The cyano-derivative was not mutagenic in the Salmonella/microsome test, with or without metabolic activation.

Animals↗
PubMed1983

Kinetic and thermodynamic parameters for oxygen binding to the allosteric states of Panulirus interruptus hemocyanin.

The temperature dependence of the oxygen binding equilibria and kinetics of Panulirus interruptus hemocyanin has been analyzed within the context of the two-state allosteric model. Oxygenation of the T-state is characterized by a more negative value of DeltaH than that of the R-state; therefore, cooperative effects in oxygen binding to P. interruptus hemocyanin are thermodynamically governed by favorable entropy changes. The allosteric transition in the unliganded derivative shows an enthalpy-entropy compensation effect. The activation enthalpies for oxygenation and deoxygenation of the T-state are larger than those for the R-state, while the activation entropies are favorable for the T-state and unfavorable for the R-state. Thus, the activation free energies for oxygen binding to the T- and R-states are similar, while for the deoxygenation reaction DeltaG++ is smaller for the T-state. The analysis reported confirms the applicability of the Monod-Wyman-Changeux two-state allosteric model to P. interruptus hemocyanin and yields a complete thermodynamic characterization of oxygen binding under both equilibrium and dynamic regimes.

Journal Article↗
PubMed1982

Spectroscopy of (carbon monoxy)hemocyanins. Phosphorescence of the binuclear carbonylated copper centers.

The luminescence of CO-hemocyanin has been studied in several hemocyanins from both arthropods and molluscs. All of them show an emission in the region 550-560 nm with quantum yield = 0.2-0.4, though individual differences are apparent. Solvent composition (as well as the presence of calcium and lanthanides) has no effect on the emission. Lifetimes of this luminescence are in the range 60-140 microseconds, indicating that the emitting state may be a triplet. The presence of both copper atoms (Cu+) per CO binding site is required for the luminescent state since half-met and half-apo derivatives do not show such an emission. Though not clearly related to any of the functional properties, systematic differences in luminescence parameters are apparent between arthropodal and molluscan hemocyanins. Limulus hemocyanin appears to be very different from both types of hemocyanin.

Animals↗
PubMed1982

Ligand binding and stereochemical effects in hemocyanins.

The Bohr effect in the binding of O(2) and CO to Helix pomatia beta-hemocyanin has been estimated by the potentiometric titration method. On the basis of the results, as well as other information available, we conclude that binding of O(2) to hemocyanin is associated with a quaternary allosteric transition (T-->R), while binding of CO is not. This conclusion is in agreement with previous results, which indicate that homotropic interactions are observed only for the binding of O(2) to the active site of hemocyanins. This is in marked contrast to the behaviour of hemoglobins which, otherwise, share with hemocyanins a number of important features, in spite of basic chemical differences. The stereochemical requirements of O(2), which forms a bridge between the two copper atoms in a site, have to be considered essential for the onset of cooperativity in hemocyanins.

Journal Article↗
PubMed1980

Root effect of Panulirus interruptus hemocyanin.

Panulirus interruptus hemocyanin exhibits a progressive decrease in oxygen affinity and a parallel loss of cooperativity with decrease in pH, resulting in an apparent loss of the oxygen-binding capacity of the protein. For a characterization of this system, oxygen-binding curves have been determined over the complete range of oxygen saturation, applying a special technique which involves high-pressure spectrophotometry. Although the oxygen-binding behavior as a function of pH is complex and cannot be described within the frame of a simple two-state Monod-Wyman-Changeux model, the observed Root effect is clearly related to a progressive stabilization of a low oxygen affinity state of the protein and functional heterogeneity is not apparent.

Animals↗
PubMed1980

Luminescence of carbon monoxide hemocyanins.

The effect of carbon monoxide on the luminescence properties of Helix pomatia alpha-hemocyanin and Panulirus interruptus hemocyanin has been studied. These proteins, when saturated with carbon monoxide, show, besides the intrinsic fluorescence arising from the aromatic amino acid residues, emission in the visible region with a maximum between 540 and 560 nm. Results of carbon monoxide titration experiments and data from absorption and excitation-emission spectra provide convincing evidence that the observed emission originates from a fluorescent copper(I)-carbon monoxide complex, and this emission is interpreted as charge-transfer luminescence.

Animals↗
PubMed1979

Sodium and calcium binding to Panulirus interruptus hemocyanin as studied by 23Na nuclear magnetic resonance.

Addition of Panulirus hemocyanin to NaCl solutions produces marked changes in the 23Na relaxation parameters; they show that sodium ions interact with binding sites on the protein and exchange rapidly with the bulk. The observed non-lorentzian lineshapes and the non-exponential decay of the transverse magnetization indicate that non-extreme narrowing conditions apply and give information on the dynamics of the interaction. Panulirus hemocyanin has at least two classes of Na+ binding sites; the binding constant of the more strongly bound sodium ions is in the order of 1 X 10(2) M-1. Competition between Na+ and Ca2+ for protein binding sites is demonstrated by the effect of Ca2+ on the 23Na relaxation parameters. However, only the more strongly bound Na+ are displaced by Ca2+. The number of Ca2+ needed to displace these sodium ions is 3--5 per oxygen binding site. The 23Na relaxation parameters are influenced also by the state of oxygenation of the protein, indicating a linkage between Na+ and oxygen binding. The simplest interpretation of the data is that sodium ions bind more strongly to oxyhemocyanin in agreement with oxygen equilibrium experiments.

Animals↗