In vitro studies on 6-fluoronoradrenaline at several peripheral sympathetic neuroeffector junctions
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A comparison of the effects of noradrenaline and 6-fluoronoradrenaline has been made at several peripheral sympathetic neuroeffector junctions. In the rat vas deferens preparation in the presence of 1 μM cocaine, 6-fluoronor-adrenaline was found to be about 9 times more potent than noradrenaline as an agonist at presynaptic inhibitory α2-adrenoceptors. In the rabbit aorta, 6-fluoronoradrenaline had approximately one tenth of the potency of noradrenaline in stimulating the postsynaptic α1-adrenoceptors. Furthermore 6-fluoronoradrenaline, in contrast to previous reports, appears to be a substrate for the neuronal uptake process since exposure to cocaine potentiated the inhibition of the twitch response of the vas deferens by 6-fluoronoradrenaline. In addition, 6-fluoronoradrenaline increased the spontaneous outflow of radioactivity from rabbit pulmonary artery strips prelabelled with 3H-noradrenaline and this increase was blocked by cocaine (30μM).
These results demonstrate that 6-fluoronoradrenaline is a preferential α2-adrenoceptor agonist which is a substrate for the neuronal uptake process in peripheral sympathetically innervated smooth muscle preparations.
Key words6-Fluoronoradrenaline Sympathetic neurotransmission Neuronal uptake α1- and α2-Adrenoceptors
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