EVIDENCE OF NITRIC-OXIDE IN THE EXHALED GAS OF ASIAN ELEPHANTS (ELEPHAS-MAXIMUS)

Nitric oxide (NO) produced in the respiratory tract is released into t he respiratory gases of humans, rabbits, guinea-pigs, and rats. We ana lysed the NO concentrations in the exhaled gas of four awake Asian ele phants. Two methods were employed: (1) exhaled gas was sampled from th e elephants' trunks with a 1 L syringe and analysed for NO concentrati ons by chemiluminescence; (2) respiratory gas was continuously aspirat ed via a thin plastic tube positioned within the trunk and on-lint ana lysed for NO concentrations by chemiluminescence. Syringe sampling (n = 4), when corrected for dilution by ambient air using linear regressi on analysis, revealed a mean NO concentration of 31 parts per billion (ppb); highest exhalatory concentrations measured during continuous su ctioning were 27 and 28 ppb (n = 2). The exhaled NO concentrations in elephants are similar to those found in humans measured with a compara ble technique. This supports the hypothesis that a size-independent 'n ormal value' of endogenous NO is provided in the airways which may con tribute to regulation of pulmonary ventilation and perfusion by autoin halation in some mammals.