Splanchnic ammonia management in genetic and dietary obesity in the rat

Three groups of 60-day-old Zucker rats: lean (Fa/Fa), obese by diet (Fa/Fa diet-obese) and genetically-obese (fa/fa) were fed ad libitum in order to study their splanchnic ammonia management. The study was also performed in 12 h food-deprived diet-obese and lean rats, to exclude a possible effect of diet composition on the parameters studied. Ammonia concentration was higher in the hepatic, portal and arterial plasma of diet-obese rats. The intestine did not contribute to a rise in the blood ammonia levels. This increase of ammonia in the blood of diet-obese rats coincides with higher alanine levels in plasma and a net glutamine production by liver. In fa/fa rats, ammonia levels were similar to those of lean rats, except for portal ammonia, which was lower. Hepatic availability of ammonia increased dramatically in diet-obese rats, but ammonia uptake by the liver was similar to that of lean rats. Conversely, hepatic availability of ammonia in fa/fa rats was similar to that of lean animals, whereas ammonia uptake by the liver was reduced to 50% of either lean or diet-obese values. Fasting for 12 h reduced plasma ammonia concentration in diet-obese rats: ammonia levels in the hepatic vein and aorta were similar to those of lean rats fasted for 12 h, whereas they were lower in the portal vein. Furthermore, ammonia hepatic availability was in the same range as that of lean animals, whereas ammonia uptake by the liver was reduced.(ABSTRACT TRUNCATED AT 250 WORDS)