The role of nitric oxide on the proximal tubule ammonia secretion in rat

In order to study the effect of nitric oxide on ammoniagenesis,the renal cortical slices obtained from, 250-300 g male Wistar rats were used in this experiment. The ammonia production and secretion were studied in the cortical slices incubated in krebs buffer with and without 1 mM glutamin for 2 h at 37° C, pH7.4 under 95% 02 and 5% C02. The ammonia secretion into the medium from the cortical slices incubated with krebs buffer for 2 h was 31.98 ± 1.76 nM/g protein and the addition of 1 mM glutamin,an ammonia precursor into incubation medium increased the ammonia secretion to 64.11 ± 2.6 |aM/g protein (p<0.001). Presence of 10"4 M L-NAME in the incubation medium significantly increased the ammonia secretion (99.14 ± 16.02(aM/g protein, p<0.01). 10'7M Angiotensin II also caused a significant increase in the medium and tissue ammonia. Neither prevention of endogenous nitric oxide production with L- NAME and lO^M L-Canavanin nor addition of 10"5 M SNAP, a nitric oxide donor, to the medium influenced the angiotensin II mediated increase in ammoniagenesis. Glutamine utilisation by the cortical slices in all groups were the same however the convertion of glutamine to ammonia increased significantly to 1.03 ± 0.04 and 0.98 ± 0.04 from 0.87 ± 0.08 (mol/mol) in the slices subjected to L-NAME and Angiotensin II respectively. The protein content of the incubation medium significantly increased in the cortical slices subjected to 1 mM glutamine for 2 h. L-NAME and Angiotensin II completely prevented glutamine mediated protein secretion but addion of SNAP overcomed the Angiotensin and L-NAME dependent suppression and the protein content of the medium returned to the control level. As a result our findings demonstrated that: 1- Angiotensin II stimulated both the production and secretion of ammonia in the renal cortical slices of rats. 2- Endogenous nitric oxide which has an inhibitory effect on ammoniagenesis is not involved, angiotensin II merdiated ammoniagenesis. 3- The significant increase in the ratio of ammonia to glutamine and decrease in medium protein contents in the presence of L-NAME and Angiotensin II indicate that these two agents prefer the Glutamate dehydrogenase pathway for their effect on ammoniagenesis.