Dual effect of agmatine in the bisected rat vas deferens.
The functional effects of the amine agmatine, the putative endogenous ligand for alpha(2)-adrenoceptors and imidazoline receptors, in rat vas deferens were investigated by using the epididymal and prostatic portions. Tissues were contracted by electrical stimulation or by exogenous drugs. In electrically stimulated portions, agmatine caused a dual effect on contractions. In the epididymal portion an inhibition on twitch contractions was observed, which was partially antagonised by idazoxan and yohimbine, indicating the involvement of at least a presynaptic alpha(2)-adrenoceptor-mediated mechanism, without the interference of imidazoline receptors. In the prostatic portion, agmatine enhanced the amplitude of twitches. In contractions induced by exogenous drugs, agmatine potentiated, only in the prostatic segment, the effects of noradrenaline (norepinephrine) or ATP; it also enhanced the effect of low concentrations of KCl and blocked the maximum effect of the higher concentrations. Effects induced by agmatine on the exogenous ATP in the prostatic portion were blocked by cromakalim, suggesting a blocking action on the postsynaptic K(+) channels, which explains, in part, the potentiation of the twitch amplitude. It was concluded that agmatine interferes with sympathetic neurotransmission, but the physiological relevance of this needs to be better understood because of the high doses employed to induce its effects.
Santos
Wilson C
WC
Departamento de Farmácia e Administração Farmacêutica, UFF, Faculdade de Farmácia, 24241-000, Niterói, RJ, Brasil. wsantos@vm.uff.br
Smaili
Soraya S
SS
Jurkiewicz
Aron
A
Piçarro
Ivan
I
Garcez-do-Carmo
Lúcia
L
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000376:Agmatine / Q000494:pharmacology*; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004822:Epididymis / Q000294:innervation / Q000502:physiology; D019329:Idazoxan / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D054755:Imidazoline Receptors; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects; D011955:Receptors, Drug / Q000819:agonists; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects; D014649:Vas Deferens / Q000187:drug effects* / Q000294:innervation; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007093:Imidazoles; D054755:Imidazoline Receptors; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug; D010643:Phenoxybenzamine; D015016:Yohimbine; D011189:Potassium Chloride; D000376:Agmatine; D000255:Adenosine Triphosphate; C043482:moxonidine; D003000:Clonidine; D009638:Norepinephrine; D019329:Idazoxan