EVIDENCE THAT NITRIC-OXIDE MODULATES DRINKING BEHAVIOR

The involvement of the L-arginine-nitric oxide (NO) pathway in brain, in the regulation of drinking behaviour, has been evaluated by injecting L-arginine and N(OMEGA)-nitro-L-arginine methyl ester (L-NAME) into the lateral cerebral ventricle (i.c.v.). L-Arginine (5 and 10-mu-g/rat), but not D-arginine, was antidipsogenic when administered to 24 hr water-deprived rats but did not change the intake of water in normally hydrated rats. However, L-NAME (5 and 10-mu-g/rat) did antagonize the effect Of L-arginine in water-deprived animals but, by itself, did not increase thirst. L-Arginine (100 ng), when injected into the preoptic area significantly reduced water deprivation-induced drinking. The same dose was unaffective when given intraventricularly. Finally, L-arginine (5 and 10-mu-g/rat, i.c.v.) inhibited drinking induced by intraventricular injection of angiotensin II (250 ng/rat). The effect was dose-dependent. The results indicate that: (1) NO acts as an inhibitory mechanism when thirst is stimulated by water deprivation or by angiotensin II; (2) the preoptic area might be one of the central sites of antidipsogenic action of NO and (3) nitric oxide synthase might be inhibited during water deprivation.