Different α‐adrenoceptors modulate the release of 5‐hydroxytryptamine and noradrenaline in rat cortex

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Abstract
1 The potassium-evoked release of [3H] -noradrenaline from slices of rat occipital cortex and the potassium-evoked release of [3H]-5-hydroxytryptamine from slices of rat frontal cortex were measured using a superfusion system. 2 The rank order of potency for a number of α-adrenoceptor agonists was different for the two neuronal systems, Clonidine and azepexole being the most potent inhibitors of noradrenaline release and methoxamine and phenylephrine being the most potent against 5-hydroxytryptamine release. 3 The rank order of potency for a series of α-adrenoceptor antagonists in reversing the inhibition of noradrenaline release produced by Clonidine was: phentolamine > rauwolscine = yohimbine = corynanthine >> WB4101, whereas against methoxamine-inhibition of 5-hydroxytryptamine release the rank order of potency was: WB4101 > phentolamine > corynanthine > yohimbine > rauwolscine. 4 The results suggest that the α-adrenoceptors which modulate potassium-evoked 5-hydroxytryptamine release are not identical with the α2-adrenoceptors located on noradrenergic nerve terminals and may more closely resemble α1-than α2-adrenoceptors.
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