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 (F a/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 12h food-deprived diet-obese and lean rats, to exclude a possible effect of diet composition on the parameters studied. Ammoni a 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-ob ese rats coincides with higher alanine levels in plasma and a net glut amine production by liver. In fa/fa rats, ammonia levels were similar to those of lean rats, except for portal ammonia, which was lower. Hep atic availability of ammonia increased dramatically in diet-obese rats , but ammonia uptake by the liver was similar to that of lean rats. Co nversely 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 p lasma ammonia concentration in diet-obese rats: ammonia levels in the hepatic vein and aorta were similar to those of lean rats fasted for 1 2 h, whereas they were lower in the portal vein. Furthermore, ammonia hepatic availability was in the same range as that of lean animals, wh ereas ammonia uptake by the liver was reduced. From these results, it can be deduced that diet-obese rats fasted for 12 h show similar behav iour to that of fa/fa rats feeding ad libitum. Fractional extraction o f ammonia by liver of diet-obese rats (ad libitum or 12 h fasted) and fa/fa rats was always less than that of lean rats. Moreover, in obesit y, the percentage arterial contribution to ammonia availability in the liver was greater than in lean animals.