Objectives　Administration of L-ornithine increases ammonia detoxification by the urea cycle in the liver. Some ammonia is secreted from the skin through sweat and gas. In this study, we examined the effect of L-ornithine intake on the transdermal secretion of ammonia evoked by ergometer exercise.
Methods　A double-blind crossover human trial was performed with 20 healthy adult Japanese men. Subjects took glycine（as a placebo）or 2.4 g L-ornithine before attending an incremental ergometer exercise. Ammonia concentrations in blood and transdermal secretions were measured before and after exercise.
Results　Incremental ergometer exercise transiently increased blood ammonia concentrations and transdermal ammonia secretion. L-ornithine ingestion significantly reduced transdermal secretion of ammonia and tended to reduce blood ammonia concentrations induced by exercise.
Conclusions　L-ornithine intake before exercise suppressed the increase in transdermal ammonia secretion. This effect of L-ornithine is probably caused by an increase in urea cycle function in the liver.