Rat metabolic adaptation to ammonia inhalation.

Rats exposed to 25 or 300 ppm NH3 vapor for 5-15 days 6 hr daily showed dose-dependent blood ammonia after 5 days. Brain and blood glutamine were also increased at the same time in rats exposed to 300 ppm. The blood ammonia concentration of the exposed rats resumed control levels at 10 and 15 days while hepatic citrulline synthesis increased above that of the controls. The animals exposed to 300 ppm NH3 showed initially a slight acidosis. As circulating ammonia decreased, brain and blood glutamine returned to the control range. Our findings support the idea that ureagenesis is aimed mainly at the removal of NH+4 with only secondary and small effects on the acid-base balance.