Development of cholinergic and inhibitory non-adrenergic non-cholinergic responses in the rat gastric funds.

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1. Cholinergic contractions and inhibitory non-adrenergic non-cholinergic (NANC) relaxations were studied in longitudinal muscle strips of the gastric funds of 2, 4 and 8 week old rats. 2. Contractions induced by electrical stimulation of the cholinergic neurones and by administration of acetylcholine decreased during development. The potentiating effect of physostigmine was similar in the 3 age groups. 3. Short train stimulation in NANC conditions induced fast relaxations, which were more pronounced in 4 and 8 week than in 2 week old rats. These relaxations were almost completely inhibited by NG-nitro-L-arginine methyl ester (L-NAME) in the 3 age groups. The nitric oxide-induced relaxations did not change during development. 4. Sustained electrical stimulation in NANC conditions induced an initial relaxation, which was almost totally blocked by L-NAME, followed by an almost complete recovery of tone at lower frequencies of stimulation. At higher frequencies of stimulation, the recovery of tone was incomplete or absent. This sustained relaxation was only partially reduced by L-NAME and almost abolished by L-NAME plus alpha-chymotrypsin. The initial relaxations increased during development, while the sustained relaxations remained similar during this period. Vasoactive intestinal polypeptide-induced relaxations were also similar in the 3 age groups. 5. These results show that the sensitivity of the gastric fundus to acetylcholine decreases from 2 weeks to 8 weeks postnatally, while the importance of the nitrergic innervation increases during this period.