6533b7d9fe1ef96bd126cabe

RESEARCH PRODUCT

Tissue Differences in the Effect of Atropine on the Evoked Release of Acetylcholine

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The effect of atropine on the release of acetylcholine (ACh) from different peripheral parasympathetically innervated tissues was investigated. My enteric plexus The longitudinal muscle-myenteric plexus preparation of the guinea-pig was incubated in eserinecontaining Tyrode solution. The ACh release evoked by high K+ (45 or 108 μ) or by the nicotinic drug dimethylphenylpiperazinium (DMPP) (10 pM) was increased by atropine (0.1–10 μ) in a concentration-dependent fashion. Muscarinic agonists (oxotremorine; propargylester of arecaidine) prevented the facilitatory effect of atropine on ACh release. These results suggest that the ACh release from the myenteric plexus is regulated via presynaptic inhibitory muscarinic receptors. Heart lsolated guinea-pig hearts were perfused with Tyrode solution in the presence of eserine. The ACh overflow during a 2-min perfusion with 108 mM K+ was not changed by atropine. Likewise, atropine did not modify the ACh output caused by 2-min perfusions of isolated chicken hearts with high K+ (45 or 108 mM) or with DMPP (300 μ) either in the absence or presence of eserine. Urinary bladder Strips of the guinea-pig urinary bladder were incubated in eserine-containing Tyrode solution. The release of ACh evoked by a 10-min incubation of the strips with 108 mM K+ was not changed by atropine. It is concluded that only the ACh release from the guinea-pig myenteric plexus can be modulated via presynaptic muscarinic-recep-tors. Apparently, the terminals of the postganglionic parasympathetic nerves of guinea-pig and chicken hearts and of guinea-pig urinary bladder are not equipped with inhibitory mus-carinic-receptors.