Mediators of nicotine-induced relaxations of the rat gastric fundus

1. Relaxations of strips of rat gastric fundus were elicited with nicotine (100 mumol/L), nitric oxide (NO; 30 mumol/L), sodium nitroprusside (SNP; 100 nmol/L) and vasoactive intestinal polypeptide (VIP; 1 nmol/L). 2. Methylene blue (30 mumol/L), an inhibitor of soluble guanylate cyclase, reduced relaxations elicited by NO and nicotine, but not those elicited by VIP. 3. Chymotrypsin (1 U/mL) abolished VIP-induced relaxations and reduced nicotine-induced relaxations, but had no effect on SNP-induced relaxations. 4. NG-nitro-L-arginine methyl ester (L-NAME; 100 mumol/L), an inhibitor of NO synthase, reduced relaxations elicited by nicotine, but not those elicited by SNP or VIP. 5. When nicotine-induced relaxations had been reduced by either L-NAME or chymotrypsin, the addition of the other agent produced a greater reduction. However, the relaxations were not abolished. 6. Nicotine-induced relaxations were abolished by tetrodotoxin (1 mumol/L) or hexamethonium (100 mumol/L), indicating that they were due to activation of neuronal nicotinic receptors. Their reduction by methylene blue and L-NAME indicates that an NO-like mediator was involved. Their reduction by chymotrypsin indicates that a VIP-like peptide was involved. However, since they were not abolished by a combination of L-NAME and chymotrypsin, it appears that at least one more as yet unidentified mediator may be involved.