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Presynaptic muscarinic receptors inhibiting endogenous noradrenaline release in the portal vein of the freely moving rat
Author(s) -
Remie R.,
Coppes R.P.,
Zaagsma J.
Publication year - 1989
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1989.tb11989.x
Subject(s) - muscarinic acetylcholine receptor , yohimbine , endocrinology , medicine , atropine , methacholine , chemistry , muscarinic agonist , inhibitory postsynaptic potential , agonist , endogeny , acetylcholine , receptor , antagonist , respiratory disease , lung
1 In the portal vein of the freely moving unanaesthetized rat, the existence of presynaptically located inhibitory muscarinic receptors was investigated by use of the muscarinic agonist methacholine (MCh) 2 Infusion of MCh (0.3 μg min −1 ) did not significantly inhibit the endogenous noradrenaline (NA) overflow in portal plasma. However, after inducing high intra‐synaptic concentrations of NA by blocking the presynaptic α 2 ‐adrenoceptors with yohimbine (1 mg kg −1 ), MCh (0.3 μg min −1 ) was able to reduce the yohimbine‐induced enhanced NA overflow by 38%. 3 The MCh‐induced inhibition was almost completely abolished after blockade of the presynaptic muscarinic receptors with atropine (0.6 mg kg −1 ). 4 During electrical stimulation of the portal vein nervous plexus the evoked NA overflow was strongly inhibited (95%) during MCh‐infusion (0.3 μg min −1 ). Again atropine (0.6 mg kg −1 ) was able to reverse this inhibition. 5 These results show the existence of presynaptic muscarinic receptors inhibiting endogenous NA overflow from the portal vein nervous plexus under conditions of enhanced sympathetic activity in the freely moving rat.