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  • Title: L-arginine-nitric oxide pathway involvement in the nerve-evoked relaxant responses of the 5-HT precontracted chick isolated upper oesophagus.
    Author: Gwee MC, Gopalakrishnakone P, Cheah LS, Bowman WC.
    Journal: J Auton Pharmacol; 1995 Jun; 15(3):151-8. PubMed ID: 7673269.
    Abstract:
    1. The effects of tetrodotoxin (TTx) and the selective nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) on relaxant responses of the 5-HT precontracted chick isolated upper oesophagus to electrical field stimulation (EFS: 25-30V, 5 Hz for 10 s, 1 ms pulse width every 100 s) were investigated; the oesophagus was mounted under 1 g tension in Krebs solution containing 1 microM atropine. Appropriate tissue sections (30 microM thickness) of the chick oesophagus were also processed for NADPH-diaphorase histochemistry. 2. TTx (2 microM) and L-NAME (100-200 microM) inhibited the relaxant responses of the 5-HT precontracted chick oesophagus to EFS in a concentration-dependent manner; L-arginine (0.5-1 mM), but not D-arginine (0.5-1 mM), reversed the inhibition by L-NAME. In the absence of atropine and muscle tone, EFS produced contractile responses of the chick oesophagus that were completely abolished by 1 microM atropine, which also blocked the contractile response to acetylcholine (50 microM). 3. Under light microscopy, NADPH-diaphorase histochemistry confirmed the presence of nitric oxide synthase (NOS)-containing neurones and nerve fibres in the chick oesophagus. 4. The relaxant responses of the 5-HT precontracted chick isolated upper oesophagus to EFS are, therefore, mediated via the stimulation of non-adrenergic non-cholinergic nerves. These are likely to correspond to the histochemically identified NOS-containing neurones involved, presumably, in the synthesis and release of nitric oxide as the relaxant (inhibitory) neurotransmitter in this avian smooth muscle.
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