Inhibition of carbonic anhydrase by nitric oxide

The aim of the present study was to follow the effect of nitric oxide (NO) on carbonic anhydrase in vitro and in vivo. The effect of L-arginine (as source of NO), as well as that of its analogue, nitro-G-monomethyl-L-arginine, an inhibitor of NO synthesis on carbonic anhydrase, were also studied. In vitro results showed that L-arginine activates carbonic anhydrase, while N-G-monomethyl-L-arginine does not modify its activity. In vivo, L-arginine and N-G-monomethyl-L-arginine increased carbonic anhydrase activity by 72% and, 160% respectively. Administration of L-arginine, as a source of NO, and of acetazolamide before administration of N-G-monomethyl-L-arginine abolished the activating effect of the analogue on carbonic anhydrase. These results lead to the conclusion that inhibition of NO synthesis by N-G-monomethyl-L-arginine induces increase of carbonic anhydrase activity. The data also suggest that NO biosynthetized from L-arginine inhibits carbonic anhydrase.