Analysis of liver tissue for olestra following long-term feeding to rats and monkeys.

The potential for olestra to be absorbed and to accumulate in tissues was investigated by analysing liver tissue from rats and monkeys in long-term feeding studies using sensitive chromatographic methods. Studies with intravenously administered olestra indicated that absorbed olestra is predominantly taken up by the liver. In monkeys, 74% of the injected dose was detected in the liver, as intact olestra, 48 hr after dosing.

Long-term performance of a gas chromatography/tandem mass spectrometry assay for tebufelone in plasma.

An automated gas chromatography/tandem mass spectrometry (GC/MS/MS) based method for the rapid determination of tebufelone (TE) in animal and human plasma has been routinely applied in our laboratory to more than 3000 samples over a 2-year period. The selectivity of MS/MS conducted on a triple quadrupole instrument, combined with the use of a stable-isotope-labeled internal standard, results in excellent analytical figures of merit, as well as minimal sample preparation, rapid analysis, and high assay reliability. The work described here goes beyond initial method development and validation studies by evaluating the long-term performance of quantitative GC/MS/MS.

Determination of total and encapsulated insulin in a vesicle formulation.

A method for the determination of the amount of insulin in a vesicle formulation was developed. Samples were treated with anion exchange resin to quantitatively remove the insulin outside the vesicle walls. Encapsulated insulin was released from vesicles by disruption with a surfactant and the amount released was determined by reversed-phase HPLC.

Quantitation of vitamin B6 in biological samples by isotope dilution mass spectrometry.

Methods have been developed for the simultaneous quantitative analysis of vitamin B6 forms in biological samples by isotope dilution mass spectrometry using deuterated forms of pyridoxine, pyridoxal, pyridoxamine, and pyridoxic acid. The biological fluid or tissue sample was homogenized and then treated with a cocktail containing appropriate amounts of each deuterated vitamer, as well as the deuterated, phosphorylated vitamer forms. The individual vitamers were isolated from the homogenate by a complex high-performance liquid chromatographic procedure that provided separate fractions for each of the six vitamers found in biological samples.

Acyl phosphate and cyclic AMP inhibition of reactions of D-glyceraldehyde-3-phosphate dehydrogenase with aldehyde and acyl phosphate substrates: multiple inhibition analysis.

The effects of the inhibitors trimethylacetyl phosphate and cAMP have been determined in reactions catalyzed by D-glyceraldehyde-3-phosphate dehydrogenase. These inhibitors must influence the oxidation of aldehydes through substrate dependent cooperative conformational changes. Both trimethylacetyl phosphate and cAMP give sigmoidal 1/V vs (I) plots in oxidation of glyceraldehyde 3-phosphate, but exert linear competitive effects on the acyl phosphatase site in acylation reactions of beta-(2-furyl) acryloyl phosphate.

Biliary lipids, bile acids, and gallbladder function in the human female: effects of contraceptive steroids.

Individuals who take contraceptive steroids or estrogens are at increased risk of developing cholesterol gallstones. The mechanisms of the increased stone formation are incompletely understood. In this study we report biliary lipid composition and secretion, bile acid composition and kinetics, and gallbladder function in a group of healthy, nonobese women taking a contraceptive steroid preparation.

A method for the accurate measurement of isotope ratios of chenodeoxycholic and cholic acids in serum.

A method for the extraction of bile acids from serum is described that enables the stable isotopic content of chenodeoxycholic acid and cholic acid to be determined accurately to levels as low as the natural 13C abundance. The method uses Sep-Pak C18 reverse phase cartridges both for extraction and purification procedures. Free bile acids, bile acid conjugates, and 3-monosulfated bile acid conjugates are recovered in high yield from the Sep-Pak in methanol-water 75:25 after first removing impurities with hexane and methanol-water 40:60 washes.

Biliary lipids, bile acids, and gallbladder function in the human female. Effects of pregnancy and the ovulatory cycle.

To study the events that might lead to an increased risk of cholesterol gallstones, we examined biliary lipid composition and secretion and bile acid composition and kinetics at different stages of pregnancy or ovulation in young, nonobese, healthy women. Lipid composition and bile acid distribution were determined in duodenal fluid obtained in the fasting state and after stimulation of the gallbladder. Biliary lipid secretion was measured by the marker-perfusion technique.

Ammonia gas: an improved reagent for chemical ionization mass spectrometry of bile acid methyl ester acetates.

The ammonia chemical ionization mass spectra of 28 methyl ester acetate derivatives of bile acids and related compounds have been determined by gas-liquid chromatography-mass spectrometry. Advantages of ammonia ionization over the previously studied isobutane ionization include a 130-270% enhancement in the sensitivity of base peak monitoring, and direct determination of molecular weight from the base peak (M + NH4+) in the mass spectrum of any of the derivatives. Minor ions in the ammonia spectra also allow selective detection of 3-keto compounds and can indicate unsaturation or double bond conjugation in the molecule.