Determination of a new 5-lipoxygenase inhibitor, zileuton, and its inactive N-dehydroxylated metabolite in plasma by high performance liquid chromatography.

A rapid and sensitive assay was developed for the measurement of plasma concentrations of zileuton racemate, a potent inhibitor of 5-lipoxygenase. Zileuton and its inactive N-dehydroxylated metabolite were extracted from human, monkey, and rat plasma by use of a solid-phase extraction column (Analytichem Bond Elut). The compounds were then separated by reverse-phase high performance liquid chromatography (HPLC) on a Supelcosil LC-18 column and quantified on the basis of ultraviolet absorption at 260nm relative to an internal standard. The extraction recovery of zileuton, as determined by HPLC assay, was 77.9 +/- 1.7%. Recovery of the metabolite was 85.8 +/- 0.7%. Calibration curves for both compounds were linear over the zileuton concentration range 0.01 to 10.0 mg/L (correlation coefficients > 0.987), while the intra- and interassay coefficients of variation were < 15.6%. In practice, > 97% of blinded daily spiked control samples for zileuton and > 90% of those for the metabolite were within 10% of their target concentrations.

Moment-length relations of rectus femoris muscles of speed skaters/cyclists and runners.

The purpose of this study was to investigate the possible existence of systematic differences between moment-length properties of the rectus femoris muscle of cyclists/speed skaters and runners. In cycling/speed skating the rectus femoris is used at a shorter length than in running because of the pronounced flexion at the hip joint. It was speculated that using the rectus femoris chronically at different lengths would result in different moment-length relations for the two groups of athletes. Moment-length relations of rectus femoris muscles were determined using an adaptation of procedures outlined in the literature. Four subjects in each group performed 13 isometric knee extensions on a Cybex II dynamometer in each of three testing sessions. Knee and hip angles were varied in a systematic way to allow the determination of moment-length relations over a wide range of normal rectus femoris lengths. It was found that cyclists tended to be stronger at short compared with long rectus femoris lengths, whereas the opposite was true for runners. This finding may be associated with an adaptation of the rectus femoris muscle to the requirements of cycling and running or may show an inherited difference in the muscles of the athletes that existed before they became involved in their respective sports. The data of this study do not allow us to distinguish between these two possible factors.