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Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery
Author(s) -
González C.,
Regunathan S.,
Reis D.J.,
Estrada C.
Publication year - 1996
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.1476-5381.1996.tb15726.x
Subject(s) - agmatine , idazoxan , methoxamine , imidazoline receptor , endocrinology , chemistry , medicine , endogeny , stimulation , biophysics , receptor , antagonist , arginine , agonist , biology , biochemistry , prazosin , amino acid
1 We investigated the vascular effects of agmatine (decarboxylated arginine), an endogenous ligand for α 2 ‐adrenoceptors and non‐adrenoceptor imidazoline (I‐) receptors, present in endothelium, smooth muscle and plasma, using the rat tail artery as a model. 2 While by itself agmatine (10 nM‐1 mM) was without effect on isolated arterial rings, at the highest concentration used (1 mM) it slightly increased EC 50 values for contractions elicited respectively by the α 1 ‐ and α 2 ‐adrenoceptor agonists methoxamine and clonidine. 3 Agmatine (0.03‐1 mM) produced a concentration‐dependent transient inhibition of the contractions induced by transmural nerve stimulation (TNS; 200 mA, 0.2 ms, 1 Hz, 10 s). This effect was abolished by the α 2 ‐adrenoceptor antagonists, rawolscine and idazoxan. 4 In the presence of rawolscine or idazoxan, agmatine produced a concentration‐dependent delayed facilitation of TNS‐induced contractions, which was prevented by cocaine. 5 Neither inhibitory nor potentiating actions were produced by agmatine on contractions induced by noradrenaline (NA) administration. 6 Agmatine did not directly affect [ 3 H]‐NA uptake in bovine cultured chromaffin cells. 7 Agmatine can regulate vascular function by two opposing actions at sympathetic nerve terminals, with different latencies: a transient inhibition of NA release mediated by prejunctional α 2 ‐adrenoceptors and a cocaine‐sensitive delayed facilitation the mechanism of which is undetermined at present. 8 The results reveal the existence of a novel endogenous amine modulating NA release in the perivascular sympathetic terminals.