Swimming-exercise increases the capacity of perfused rat liver to produce urea from ammonia and L-glutamine

We designed this study to determine whether the capacity of the liver to up take ammonia and produce urea was affected by exercise (swimming at 24 degr ees C with a 2.5% extra body-weight load). For this purpose, livers from se dentary rats at rest were perfused with a buffer containing increasing conc entration of NH4Cl. The maximal hepatic capacity to produce urea was found at an NH4Cl concentration of 0.25 mM. Based on this finding all experiments with livers obtained from rats subject to swimming exercise were also carr ied out with a NH4Cl concentration of 0.25mM. Thus, employing this concentr ation of ammonia, livers from sedentary and endurance trained rats, (for a period of 11 days), that had either been resting or had been subjected to s wimming exercise for 5 min or until exhaustion, were perfused in situ and a mmonia uptake and urea production were measured. Clearly, both parameters w ere increased by exercise. However, these changes were not affected by swim ming training. In addition, we demonstrate that the effect of an acute exer cise on hepatic metabolism is not restricted to ammonia metabolism since li vers from sedentary rats which had been subjected to swimming exercise for 5 min or until exhaustion showed higher urea production from L-glutamine. Our results also suggest that part of the changes in ureogenesis induced by exercise is mediated by cortisol (increased ammonia uptake) and part of th e changes is mediated by glucagon (urea production).