Local Observation of Field Polarity Dependent Flux Pinning by Magnetic Dipoles.

A scanning Hall probe microscope is used to study flux pinning in a thin superconducting Pb film covering a square array of single-domain Co dots with in-plane magnetization. We show that single flux quanta of opposite sign thread the superconducting film below T(c) at the opposite poles of these dipoles. Depending on the polarity of the applied field, flux lines are attracted to a specific pole of the dipoles, due to the direct interaction with the vortexlike structures induced by the local stray field.

Evidence for the presence of endogenous 19-nortestosterone in the cow peripartum and in the neonatal calf.

Urine samples were collected from five Brown Swiss cows during the 18 days prior to and 11 days after parturition and were analysed for 19-nortestosterone using an enzyme immunoassay. Nortestosterone concentrations ranged from 70 to 130 nmol/l in all samples taken before parturition. The levels declined within two days, and 11 days post partum no nortestosterone was detectable. In urine from newborn calves, maximal nortestosterone concentrations were determined during the first day of life (10.9-120 nmol/l), declining below 7.3 nmol/l until day 3 in most animals and remaining below the detection limit (less than 3.6 nmol/l) after day 8 in all animals. There was no obvious difference between cows carrying a male or a female calf nor between newborn male or female calves. Using the combined methods high performance liquid chromatography/enzyme immunoassay and high performance liquid chromatography/gas chromatography-mass spectrometry, the immunoreactivity in urine was identified to be 19-nortestosterone-17 alpha. Although there is unequivocal evidence for the endogenous production of nortestosterone in pregnant cows, its function for placenta physiology, pregnancy anabolism and parturition remains unclear. However, new threshold levels for residue control of nortestosterone need to be fixed in accordance with the endocrine status of the animals.

Development of a competitive enzyme immunoassay for 17 alpha-19-nortestosterone.

Because 17 beta-19-nortestosterone and its esters are frequently used anabolic steroids in cattle in Europe, there is a need for an assay that can also detect certain metabolites. The enzyme immunoassay described here involves the detection and quantitation of the major metabolite 17 alpha-19-nortestosterone in urine. The assay is based on the coating of an antibody raised in a rabbit against 17 alpha-19-nortestosterone-3-carboxy-methyloxime-bovine serum albumin (17 alpha-19-NT-3-CMO-BSA), the competitive incubation of 17 alpha-19-NT and the 17 alpha-19-nortestosterone-3-CMO-horseradish peroxidase label, followed by the detection of the blue colour developed by the action of the enzyme on tetramethylbenzidine. The 3-CMO conjugate of 17 alpha-19-nortestosterone was used to produce an antibody with selective affinity for the 17 alpha-epimer. For the optimization of the assay, different coatings and incubation conditions were tested. The standard curve ranged between 0.98 and 4000 pg per well, with a B/B0 50% of +/- 65 pg per well. Colour was measured with a microtitre plate reader. The method was validated by means of certified blank and spiked cattle urine samples.

Quantitative analysis of anabolics on thin-layer chromatographic plates using image analysis techniques.

A new detection system is introduced for the quantitative analysis of thin-layer chromatographic plates, which is based on a relatively simple, cheap but advanced image analysis system. Both one- and two-dimensional plates can be analysed. Recording and analysis can also be performed from photographs or even slides. Applications are shown for a number of samples containing anabolic compounds.

Thin-layer chromatographic method for the detection of anabolics in fatty tissues.

A modification of the method of Verbeke [J. Chromatogr., 177 (1979) 69] is presented. The fatty tissue is dissolved in hexane, partitioned against methanol-sodium acetate buffer (pH 5.2) and extracted with dichloromethane. The crude extract is then purified on a disposable C18 column. The final extract together with a set of reference compounds is spotted on two opposite sides of a high-performance thin-layer chromatographic plate (10 X 10 cm), which is developed with two different eluents in two opposite directions. This mode of operation has the advantage that more reference compounds can be spotted and that the identification is based on two independent chromatographic runs. Also the total analysis time is decreased.

Chemiluminescence immunoassay for the detection and quantification of methyltestosterone residues in muscle tissue.

Chemiluminescence as a detection method for immunoassay has successfully been applied to the measurement of methyltestosterone (MT) residues in muscle tissue. The sample is digested enzymatically, extracted with diethyl ether and purified on a Lipidex-5000 column. An optional clean-up utilized disposable C18 columns. As the luminescent label the N-(4-aminobutyl)-N-ethylisoluminol conjugate of MT was used. The antiserum was raised in a rabbit against MT-3-carboxymethyloxime-bovine serum albumin. The detection limit of the assay was 14 +/- 7 pg (n = 13), with a limit of quantification in muscle tissue of 0.125 ppb.