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-argin ine (as source of NO), as,yell as that of its analogue nitro-G-monomet hyl-L-arginine, an inhibitor of NO synthesis on carbonic anhydrase, we re also studied. In vitro results showed that L-arginine activates car bonic anhydrase, while N-G-monomethyl-L-arginine does not modify its a ctivity. In vivo, L-arginine and N-G-monomethyl-L-arginine inn eased c arbonic anhydrase activity by 72 % and 160 % respectively. Administrat ion of L-arginine, as a source of NO, and of acetazolamide before admi nistration of N-G-monomethyl-L-arginine abolished the activating effec t of the analogue on carbonic anhydrase. These results lead to the con clusion that inhibition of NO synthesis by N-G-monomethyl-L-arginine i nduces increase of carbonic anhydrase activity. The data also suggest that NO biosynthetized from L-arginine inhibits carbonic anhydrase.