FUNCTIONAL-PROPERTIES OF AGMATINE IN RAT VAS-DEFERENS

Experiments were performed with rat vas deferens to verify whether agm atine, an endogenous ligand for adrenoceptors and imidazoline receptor s, can influence sympathetic neurotransmission, with respect to contra ctions induced by transmural nerve stimulation, contractions induced b y exogenous noradrenaline, and overflow of endogenous noradrenaline. I t was shown that agmatine (a) caused a dose-dependent potentiation of electrically induced twitches, up to about 70% in relation to controls , (b) shifted to the right the inhibitory concentration-response curve s for clonidine on electrically induced twitches, indicating competiti ve antagonism at presynaptic ol-adrenoceptors, with a pA(2) value of 4 .12 +/- 0.10, (c) shifted to the right the concentration-response curv es for noradrenaline-induced contractions, indicating competitive anta gonism at postsynaptic alpha-adrenoceptors as well, with a pA(2) value of 4.03 +/- 0.10, and (d) caused a dose-dependent increase of KCl-ind uced overflow of noradrenaline, up to about 90% in relation to control s. It is concluded that agmatine has multiple effects on sympathetic n eurotransmission in rat vas deferens.