Detection of nitric oxide in exhaled air of different animal species using a clinical chemiluminescence analyser

The aim of the present study was to evaluate the nitric oxide (NO) concentrations present in end-expired gas (FENO) of different animal species under basal and stimulated conditions using a clinical chemiluminescence analyser, which has been developed for measurement of single exhalations in humans. Anaesthetised, tracheotomised and artificially ventilated guinea pigs, rats and rabbits were prepared for recording systemic blood pressure and FENO. Stable levels of FENO were detected in expired air over a 1-h observation period in the three animal species tested. Rabbits exhibited the highest concentrations and output (FENO 12.9 ± 1.0 ppb, VNO 9.0 ± 0.7 nl min^-1), followed by guinea pigs (FENO 6.2 ± 0.70 ppb, VNO 1.7 ± 0.19 nl min^-1) and rats (FENO 0.9 ± 0.01 ppb, VNO 0.25 ± 0.00 nl min^-1). L-Arginine (1 g kg^-1 i.v.) evoked significant increments in VNO in guinea pigs and rabbits but was ineffective in rats. However, L-arginine showed a direct effect on blood pressure in all the animal species tested, causing a rapid fall in the mean arterial blood pressure (MABP; 38, 48 and 50% decrease in rabbits, guinea pigs and rats, respectively; P <0.05). An inhibitor of endogenous NO synthesis, N(G)-nitro-L-arginine methyl ester (L-NAME, 20 mg kg^-1 i.v.), decreased both basal and L-arginine-induced VNO in guinea pigs and rabbits, but was ineffective in rats. L-NAME increased MABP in all the animal species tested (58% in guinea pigs, 43% in rats and 18% in rabbits; P <0.05). The results indicate that it is possible to detect NO in the exhaled air of different animal species using a clinical chemiluminescence analyser and that different species exhibit striking differences in the levels of basal and stimulated NO output.