Studies on the location of catecholamine receptors in canine sympathetic ganglia

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: α 1- and α 2-adrenoceptors and dopamine D 2 receptors. Activation of α 1-adrenoceptors or dopamine D 2 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 α 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 α 1-adrenoceptors and dopamine D 2 receptors located proximal to the synapse of the pre- and postganglionic neurons and the other involved α 2-adrenoceptors located distal to the intraganglionic synapse.