Microdialysis of insulin-like growth factor-I in human muscle.

The determination of the insulin like growth factor I (IGF-I) concentration in the interstitial milieu is of outstanding importance to explore its autocrine/paracrine function. We previously reported a method to calibrate microdialysis probes for lactate and glucose (slope method). In the present study, we investigated the ability of our method to determine the concentration of larger molecules, such as IGF-I. We observed in vitro a close linear relationship (r = 0.86, P < 0.0005) between the recoveries of lactate (RecLac) and of IGF-I (RecIGF-I), giving access to the measurement of IGF-I with the same accuracy as the one previously found for lactate and glucose. In seven human volunteers, we calibrated each probe with the slope method: we first determined in vivo for every probe the specific RecLac/loss ethanol relationship and thereafter, using that relationship, we deduced RecLac from the loss ethanol value measured in every dialysate. This allowed calculation of RecIGF-I from the calculated RecLac value and the in vitro RecLac/RecIGF-I relationship, and finally free IGF-I concentration in muscle interstitial fluid. The mean free IGF-I interstitial concentration was 6.8 +/- 3.2 ng/ml while the mean plasma concentration was 0.4 +/- 0.2 ng/ml. This large gradient from interstitium to plasma for free IGF-I could be related to the local action of this growth factor.

Validation of a new calibration method for human muscle microdialysis at rest and during exercise.

Microdialysis presents the unique possibility to measure metabolite concentrations in human interstitial fluid. During exercise, the recovery of these metabolites should be precisely monitored since it is known to increase greatly with muscle blood flow. The loss of ethanol, perfused at low concentration, can be accurately measured and reflects the changes in dialysis conditions. We evaluated whether using the relationship determined in resting metabolic conditions between the loss of ethanol, as reference substance, and the recovery for lactate or glucose would allow us to calculate precisely the concentration of these substances and their variations during exercise. Using the new catheter calibration method (slope method), the error of estimation of lactate and glucose in vitro was limited to -0.6 (5.8)% and -0.7 (6.2)%, respectively. In resting human muscle, the slope method proved to be as accurate as an established calibration technique ("no net flux method") to evaluate interstitial lactate concentration [1.82 (0.58) vs 1.83 (0.47) mM, respectively]. During dynamic knee-extension exercise or light neuromuscular electrical stimulation, the estimated interstitial lactate and glucose concentrations varied differently, but their time course changes remained consistent with their respective plasma values. We conclude that, after an initial calibration step, the slope method allows accurate measurement of interstitial muscle metabolites and it could be used to monitor rapid metabolic changes during exercise.

Comparison of ELISA method versus MEIA method for daily practice in the therapeutic monitoring of tacrolimus.

BACKGROUND: For the adequate management of transplant patients on tacrolimus therapy, it is important to obtain optimal blood concentrations. The purpose of this study was to determine the most appropriate method for daily practice of tacrolimus determination in whole blood. We compared enzyme-linked immunosorbent assay (ELISA) with microparticle enzyme immunoassay (MEIA), using European controls and blood samples from organ graft recipients treated with tacrolimus. Time, practicability and cost were considered also. METHODS: The assays were performed according to the procedures detailed in the product inserts. In five European controls and 40 blood samples from kidney and liver transplant patients, we determined the blood levels of tacrolimus by both MEIA and ELISA tests. RESULTS: MEIA gave more reliable results with the European controls (y=1.078x+0.092; r=0.996) than ELISA (y=0.956x+1.307; r=0.946). For the patient samples, the correlation between the two tests was 0.85 and the extreme range of values was +65% and -56% for ELISA vs MEIA. Although the manufacturer of the ELISA test used claims the best sensitivity and precision, in our experience the MEIA test was quicker and cheaper. CONCLUSIONS: MEIA provides a quick, reliable and easy-to-handle method for routine monitoring of tacrolimus blood levels.

Simultaneous screening and quantitation of alpidem, zolpidem, buspirone and benzodiazepines by dual-channel gas chromatography using electron-capture and nitrogen-phosphorus detection after solid-phase extraction.

A rapid twin-column gas chromatographic (GC) method for simultaneous screening and determination of commonly prescribed benzodiazepines and other new anxiolytics from plasma is described. Identical fused-silica Ultra 2 (5% phenyl methyl silicone) columns were connected to nitrogen-phosphorus and electron-capture detectors. The drugs were isolated from 1 ml of plasma by solid-phase extraction (SPE) onto a C8 reversed-phase sorbent and recovered with 0.5% acetic acid in methanol. The eluate was reconstituted with isopropanol which was found suitable for on-column injection. Prazepam was used as internal standard. The method was found appropriate for the quantification in a single run of alpidem, alprazolam, buspirone, chlordiazepoxide, clobazam, clotiazepam, diazepam, estazolam, flunitrazepam, lorazepam, midazolam, oxazepam, tofisopam, triazolam, and zolpidem within 30 min. Limits of quantification allow toxicological or pharmacological determinations, except for buspirone: only toxic blood levels can be quantified by this method. This first SPE of imidazopyridines (alpidem and zolpidem) provides faster, more efficient and cheaper sample preparation than the traditional liquid-liquid procedure. This GC analysis of alpidem and zolpidem is also the first described procedure for simultaneous quantification of all different classes of anxiolytics.

Gas chromatographic determination of zopiclone in plasma after solid-phase extraction.

A gas chromatographic technique for determining zopiclone based on a solid-phase extraction procedure with C18 cartridge for sample clean-up is presented. Quantification can be achieved with 1 ml of plasma. The method uses prazepam as internal standard. Zopiclone is separated on a 5% phenyl methyl silicone analytical column and detected with an electron-capture detector, which consequently allows a limit of quantitation of 2 micrograms/l. It is thus simple, rapid, sensitive and linear over the range 5-2000 micrograms/l.

Gas chromatographic determination of meprobamate in serum or plasma after solid-phase extraction.

This gas chromatographic technique of determining meprobamate is based on a solid-phase extraction permitting a time reduction of the analysis and improving sensitivity. Quantification is realized on 500 microliters of plasma. The method uses etidocaine as internal standard and does not require derivatization. Thus it is simple, rapid, sensitive and applicable in forensic and clinical toxicological laboratories.