In vivo effects of noradrenaline and noradrenergic receptor agonists and antagonists on rat cerebellar cyclic GMP levels
Abstract
Cerebellar cyclic GMP levels can be altered by neurotransmitters and their receptor agonists and antagonists. In this study, we investigated the action of noradrenaline and certain drugs affecting alpha- and beta-adrenoceptors on rat cerebellaceptor agonists such as methoxamine and phenylephrine increased cGMP levels. alpha-Adrenoceptor antagonists such as phentolamine, phenoxybenzamine and ARC 239 decreased cGMP levels, whereas yohimbine and piperoxane which are known to act as presynaptic alpha-adrenoceptor antagonists had no effect. The action of clonidine which decreased cGMP levels at low doses was probably due to the fact that this adrenoceptor agonist inhibited the release of noradrenaline from adrenergic nerve terminals, since piperoxane injected prior to clonidine antagonized the effect of clonidine on cerebellar cGMP, and since pretreatment of the animals with 6-hydroxydopamine partially antagonized the effect of clonidine. Isoproterenol, a beta-noradrenergic agonist had no effect on cerebellar cGMP levels. Propranolol, a beta-noradrenergic antagonist decreased cGMP levels. Phenoxybenzamine or propranolol injected prior to noradrenaline decreased cerebellar cGMP.
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Potentiative action of alpha- and beta-adrenergic receptor stimulation in inducing lordosis behavior
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