PubMed · 6238
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D Krause. 1976-05-05. [Sympatholytics].. https://pubmed.ncbi.nlm.nih.gov/6238/
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The intracerebroventricular (i.c.v.) injection of clonidine, xylazine, adrenaline and methoxamine elicited dose-dependent vomiting in cats in that order of potency. The vomiting induced by clonidine, xylazine and adrenaline was antagonized by i.c.v. yohimbine and phentolamine possessing alpha 2-adrenoceptor-blocking activity, but not by prazosin showing alpha 1-adrenoceptor-blocking activity. In contrast, methoxamine-induced vomiting was antagonized by prazosin, but not by yohimbine. The vomiting induced by xylazine and adrenaline was not prevented by i.c.v. 6-hydroxydopamine treatment, but was prevented by i.c.v. reserpine treatment. Ablation of the area postrema with some damage to extremely adjacent areas abolished the vomiting induced by each alpha-adrenoceptor agonist. These results indicate that both central alpha 1- and alpha 2-adrenoceptors are involved in the emetic pathway in cats, although alpha 2-adrenoceptors seem to have the main role. It is also suggested that monoamines, and in particular 5-hydroxytryptamine in the brain, are involved in the regulation of alpha-adrenoceptor-mediated vomiting.
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Receptors mediating catecholamine-induced inhibition were studied in cardiac ganglia of pentobarbital-anesthetized dogs. Using selective agonists and antagonists the presence of three receptor subtypes was verified: alpha 1- and alpha 2-adrenoceptors and dopamine D2 receptors. Activation of alpha 1-adrenoceptors or dopamine D2 receptors reduced the response to preganglionic nerve stimulation but not to direct stimulation of the nicotinic acetylcholine receptors of the principal ganglion cells: response to both types of stimulation were reduced by activation of ganglionic alpha 2-adrenoceptors. These results suggested that two inhibitory systems were present in canine sympathetic ganglia and mediated the effects of exogenous catecholamines. One system involved alpha 1-adrenoceptors and dopamine D2 receptors located proximal to the synapse of the pre- and postganglionic neurons and the other involved alpha 2-adrenoceptors located distal to the intraganglionic synapse.