Search

Profiling of rat plasma using a highly sensitive LC-ARC-MS technique showed that [(3)H] mefenamic acid was metabolized to several products, including a sulfate conjugate and a hydroxylated analogue as major metabolites. This technique of detecting low levels of radioactivity in plasma was superior to previously used methods, such as beta-RAM detectors.

The formation of reactive metabolites from a number of compounds was studied in vitro using a mixture of non-labeled and stable isotope labeled glutathione (GSH) as a trapping agent. GSH was labeled by incorporating [1,2-(13)C(2),(15)N]glycine into the tripeptide to give an overall increase of 3 Da over the naturally occurring substance. Detection and characterization of reactive metabolites was greatly facilitated by using the data-dependent scanning features of the linear ion trap mass spectrometers to give complimentary and confirmatory data in a single analytical run. A comparison was made by analyzing the samples simultaneously on a triple-stage quadrupole mass spectrometer operated in the constant neutral loss mode. The compounds studied included 2-acetamidophenol, 3-acetamidophenol, 4-acetamidophenol (acetaminophen), and flufenamic acid. GSH adducts for each of these compounds produced a characteristic pattern of 'twin ions' separated by 3 Da in the mass spectral data. This greatly facilitated the detection and characterization of any GSH-related adducts present in the microsomal extracts. Furthermore, characterization of these adducts was greatly facilitated by the rapid scanning capability of linear ion trap instruments that provided full-scan, MS/MS and MS(3) data in one single analysis. This method of detecting and characterizing reactive metabolites generated in vitro was found to be far superior to any of the existing methods previously employed in this laboratory. The combination of two techniques, stable isotope labeled glutathione and linear ion traps, provided a very sensitive and specific method of identifying compounds capable of producing reactive metabolites in a discovery setting. The complimentary set of mass spectral data (including full-scan, MS/MS and MS(3) mass spectra), obtained rapidly in a single analysis with the linear ion trap instruments, greatly accelerated identification of metabolically bioactivated soft spots on the molecules. This in turn enabled chemists to rapidly design out the potential metabolic liability from the back-up compounds by making appropriate structural modifications.

Heart rate behaviour and the incidence of arrhythmia were recorded in 29 young subjects aged between 16 and 20 years using radiotelemetry equipment. The study consisted of four regimens: 100m freestyle swimming with and without an aqualung, up to 50m under water swimming without a breathing apparatus (skin diving) and 100m under water swimming with an aqualung (scuba diving). In the course of the swimming experiments the heart rate tracing exhibits three phases, namely: (a) a sharp rise in the first 10 s; (b) a reduction in the rate of increase, and (c) a constant plateau at approximately 184 bpm without an aqualung and 168 bpm with an aqualung. During apnoeic diving there is a slight increase in heart rate, followed by a rapid drop (vasovagal diver's bradycardia) and finally a plateau at approximately 55 bpm. Diver's bradycardia does not occur when the diver uses an aqualung; the heart rates then correspond to those observed during swimming (maximal rate approximately 169 bpm). Cardiac arrhythmia occurred in 18 instances (3 each during swimming with and without a breathing apparatus, 5 during diving with an aqualung and 7 during diving without an aqualung). 15 were cases of supraventricular extrasystoles, 12 occurred in the plateau phase. A man with a thorough endurance training exhibited in addition to supraventricular extrasystoles a transient bigeminy, substitutive AV systoles and an electric alternans during diving without an aqualung. He experienced no subjective feeling of impairment of performance, nor was there any objective reduction in efficiency.