Isolation and measurement of15N2from respiratory gases of animals administered15N‐labeled substances

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Abstract
A method is described for collection of metabolic 15N2 from in vitro preparations or intact rats administered 15N‐containing compounds. The method enables routine collection and mass spectrometric measurement of as little as 10 μmol 15N2 respired by a rat over a 24‐h period. A device is described that includes either an animal chamber or a tissue reaction vessel in a closed recycling atmosphere, with automatic O2 replenishment and removal of CO2 and water. It is capable of sustaining moderate vacuum and is coupled to a high‐vacuum manifold designed to process the contained atmosphere and respiratory gases. The starting atmosphere is an 80:20 mix of sulfur hexafluoride and O2. Recovery of 15N2 gas from the system without an animal present was 101.3 ± 5. 75%. When 15N2 gas was very slowly infused iv into an animal, recovery was 89.1 ± 5.38%. Use of the method in studies of the fate of [15N]hydrazine in rats indicated that about 15% of the administered hydrazine is rapidly converted to 15N2, followed by slower conversion of an additional 7–10% over the next several hours.