Mediation by nitric oxide formation in the preoptic area of endotoxin and tumour necrosis factor-induced inhibition of water intake in the rat.
1. Drinking was induced in rats by 24 h of water deprivation. Water intake (ml) was evaluated for a 1 h period. 2. NG-nitro-L-arginine methyl ester (L-NAME, 5-10 micrograms, i.c.v., 50-100 ng into the preoptic area (POA)), an inhibitor of nitric oxide (NO) synthase, and methylene blue (50-100 ng into POA), an inhibitor of guanylate cyclase activation, antagonized the inhibition of drinking induced by E. coli endotoxin (LPS, 640 micrograms kg-1, i.v.) and tumour necrosis factor (TNF alpha, 40 ng, i.c.v.) in 24 h water-deprived rats. 3. L-Arginine (25, 50 and 100 ng), the precursor amino acid of NO, but not the stereoisomer D-arginine (100 ng), inhibited drinking induced by water deprivation when injected into the POA 30 min before water presentation (74.4% of inhibition with the highest dose). A dose of 12.5 ng L-arginine into the POA did not exhibit antidipsogenic effects. 4. TNF alpha (20 and 40 ng, i.c.v.; 1.25, 2.5 and 5 ng into the POA) showed a dose-dependent and powerful inhibition of drinking behaviour in water-deprived rats (70.4% and 80.8%, i.c.v. and into POA, with the highest doses, respectively). A dose of 10 ng of TNF alpha given i.c.v. had no effect on the intake of water. 5. LPS and TNF alpha, given at doses (160 micrograms kg-1, i.v. and 10 ng, i.c.v., respectively) that did not influence drinking in water-deprived rats, exhibited a strong antidipsogenic effect in water-deprived rats treated with a dose of L-arginine (12.5 ng, into the POA) which did not modify drinking by itself. (LPS + L-arginine:53.6% of inhibition; TNFalpha + L-arginine: 52.0% of inhibition).6. These results suggest that NO into the POA: (1) acts as an inhibitory mechanism on thirst and (2)plays a role in the antidipsogenic effect of LPS and TNFalpha.
Calapai
G
G
Institute of Pharmacology, Faculty of Medicine, University of Messina, Italy.
Mazzaglia
G
G
Cilia
M
M
Zingarelli
B
B
Squadrito
F
F
Caputi
A P
AP
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D004326:Drinking / Q000187:drug effects*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000502:physiology*; D011301:Preoptic Area / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D001120:Arginine; D008751:Methylene Blue; D019331:NG-Nitroarginine Methyl Ester