View - ResearchSpace@Auckland - The University of Auckland

concentration can form the superoxide perioxynitrite (OONO). In part the effects of these
gases have been covered when reviewing the noxious effects of air pollution with particular
reference to the nitrogen oxides in Chapter 2.2. NO and, even more so, NOz are common air
pollutants (Morrow 1984; Anonymous 1995; Anonymous 1996) with inspired NO
concentrations from airway pollution ranging from 20-500ppb in non-polluted areas to
1.5ppm or greater in polluted areas (Aranda and Pearl 2000). As previously mentioned,
cigarette smoke contains NO concentrations in order of lOOppm (Norman and Keith 1965), or
higher depending on the cigarette type (Borland and Higenbottam 1987) and cigarette smoke
can inhibit NADPH and myeloperoxidase (Nguyen, Finkelstein et al. 2001). While this does
not result in an acute respiratory event, it might cause an increase risk of mutations over time
and thus it contributes to cigarette smoke carcinogenic potential.
With the use of nitrous oxide (NzO, "laughing gas") effects were noted when N2O cylinders
were contaminated with NO showing that high NO concentrations could give rise to acute
pulmonary oedema and methamoglobinaemia (Anonymous 1967; Clutton-Brock 1967). High
levels of NO were needed to get this response in experiments with animals. For example,
exposure of lambs to 80ppm of NO for three hours in 2l%o oxygen did not result
methaemoglobinaemia or any of the acute problems previously documented (Frostell, Fratacci
et al. 1991). Exposure of dogs to 20,000ppm did result in this acute respiratory event with
high morbidity and mortality (Shiel 1967). Inhalation of 50ppm of NO impairs the
performance of learned tasks and prolongs brainstem evoked potential responses in rats,
without significantly elevating methaemoglobin levels (Groll-Knapp, Haider et al. 1988). In
healthy subjects inhaling lOOppm of NO for three hours, methaemoglobulin levels increased
by I.77Vo of total haemoglobin to a peak at 45 minutes. Serum nitrogen oxides (NOz, NOI)
increased from 36.7 to 124umol L-l at 172 minutes and then declined (Young, Sear et al.
1996). Inhaled NO at 5ppm resulted in thickened alveolar membranes in rabbits (Hugod
1979) and NO at 43ppm and NO2 at 3.6ppm narrowed the surfactant hysteresis, altered
epithelium ultra-structure and caused interstitial atrophy (Hugod 1979). Intermittent NO
exposure over a 9 week period in rats resulted in degeneration of interstitial cells and the
interstitial matrix leading to an emphysematous-like destruction of alveolar septa (Mercer,
Cosra et al. 1995).
NOz is more toxic and has long been known to cause respiratory damage and fatality
(Kooiker, Schuman et al. 1963: Wagner, 1965 #1030). It was early recognised as a concern in
atmospheric pollution (Kennebeck, Wetherington et al. 1963). NOz has been shown to be
taken up easily by lung lining fluid at a rate related to its speed of reaction to glutathione
105