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Biomedical subjects

W Soederhuizen

Publications and source records attributed to W Soederhuizen.

7 recordsLinked to original sources
PubMed1996

Urine samples before dinner are preferable when studying changes in endogenous nitrate production under uncontrolled dietary conditions.

Changes in nitric oxide production result in changes in nitrate excretion, but these are difficult to detect if the daily intake of nitrate varies substantially. Instead of using a sample of the combined urine produced in 24 h for analysis, we studied the urine nitrate concentration in urine discharge at various times of the day. This was done with urine samples from each of seven men after a high dietary nitrate intake, followed by a low dietary intake 24 h later. The lowest variability in nitrate concentration was found in the samples before dinner (late afternoon) (511 +/- 201 (S.D.) mumol/l). However, the pre-dinner samples after a day with a nitrate-rich meal had still a 40% increased nitrate concentration (623 +/- 147 mumol/l), when compared with samples before the high nitrate diet (440 +/- 90 mumol/l; P < 0.05). This effect disappeared on the second day after the high nitrate meal (476 +/- 108 mumol/l). Similar results were found when using the nitrate/creatinine ratio. We conclude that urine samples taken before nitrate rich meals are the most reliable samples for estimating (changes in) endogenous nitrate production.

Adult↗
PubMed1985

A semi-automated and standardized method of determining the lamellar body content of amniotic fluid.

We have simplified and standardized the method of determining the lamellar bodies (LB) in amniotic fluid as a measure of fetal lung maturity. For this purpose we have first diluted the amniotic fluid and then concentrated its LB by low-speed centrifugation at the interface of a 10% Nycodenz solution. As a standard we use liposomes which consist of phospholipids enclosing a Nycodenz solution with a density similar to that of the LB. The phosphorus content of the LB and liposome standard is then determined by an automated fluorimetric method. There is an excellent correlation between the newly described procedure and the lecithin/sphingomyelin ratio. One technician can easily analyse 40 samples in a working day.

Amniotic Fluid↗
PubMed1985

The fluorimetric determination of the lecithin/sphingomyelin ratio of amniotic fluid after HPLC.

We have investigated whether fluorimetric determination of the lecithin/sphingomyelin ratio is feasible after HPLC. We found that the saturated phospholipid, dipalmitoyl lecithin, which is secreted by the fetal lung, and which cannot be detected by ultraviolet spectrophotometry, can be determined fluorimetrically. For this purpose we have added the fluorescence-enhancing substance, 1,6-diphenyl-1,3,5-hexatriene to the effluent. With the aid of a continuous-flow system we showed that the method can be used for a rapid assay of the ratio of these phospholipids in amniotic fluid.

Amniotic Fluid↗
PubMed1983

Fluorometric procedure for determining "lamellar body" phospholipids in the particulate fraction of amniotic fluid after filtration.

A rapid (30-min) semiautomated continuous-flow procedure is described for use in assessing the phospholipids of the particulate ("lamellar body") fraction of human amniotic fluid. The method is based on measuring the difference in fluorescence of 1,6,-diphenyl-1,3,5-hexatriene added to amniotic fluid before and after micropore filtration. The filtration step removes "lamellar body" particles, which are considered to contain the fetal lung surfactant. The phospholipid values for the filtered particles are independent of background fluorescence, which increases when amniotic fluid is contaminated by bilirubin pigments or blood components. Over a wide range (3-150 mumols/L) the fluorescence increases linearly with the phospholipid concentration of the amniotic fluid. There is a good agreement between the value for particulate "lamellar body" phospholipid, the ratio of the "lamellar body" phospholipids to total amniotic fluid phospholipids, and the lecithin/sphingomyelin ratio.

Amniotic Fluid↗
PubMed1982

Comparison of the values for filter-trapped phospholipids with those for the lecithin/sphingomyelin ratio of amniotic fluid. A preliminary report.

A comparison was made between the lecithin/sphingomyelin ratio of amniotic fluid and the amount of phospholipids which could be removed from the amniotic fluid by filtration. We found a good correlation between the two methods. The amount of filter-trapped phospholipids can be determined within one and a half hours compared to three and a half hours for the lecithin/sphingomyelin ratio. It has a higher reproducibility than the lecithin/sphingomyelin ratio and can be performed with the aid of a simple filtration apparatus.

Amniotic Fluid↗
PubMed1978

A rapid semi-automated method of determining total estrogens in non-pregnancy urine.

A rapid routine method of determining estrogens in non-pregnancy urine is described. It involves the following steps: 1) Dilution of each urine sample with an equal volume of saturated ammonium sulfate solution; 2) Addition of Sephadex G-15 beads; 3) Filtration of the mixture; 4) Liberation of the estrogens from the Sephadex by washing the beads on the filter with 0.1N NaOH; 5) Automated fluorimetric analysis of the alkaline filtrate according to the procedure used for the determination of estrogen in pregnancy urine. A correction for non-specific fluorescence remains necessary and is achieved by measuring background fluorescence with a second fluorimeter.

Chromatography, Gel↗