Neuroeffector transmission of the hepatic and pancreatico-duodenal isolated arteries of the dog.
Direct evidence has been obtained that the neurogenic responses of the hepatic and pancreatico-duodenal arteries of the dog are mainly due to norepinephrine released from varicosities and that this effect is mediated via alpha 1-adrenoceptors. In addition, there is a prazosin-resistant response to nerve stimulation that is certainly not mediated via alpha 2-adrenoceptors. These vessels are 10-100 times less sensitive to applied norepinephrine than the great majority of peripheral arteries; however, the pA2 value for prazosin (7.5) is the same as in other systems. The varicose terminal plexus is located deep in the media, as shown by electron microscopic study. Findings indicate that these gastrointestinal arteries are mainly controlled by adrenergic innervation, that their density is as high as that of any other vessel, and that these arteries might be much less influenced by the circulating catecholamines than others. The neuroeffector transmission of hepatic and pancreatico-duodenal arteries is subject to presynaptic modulation. Muscarinic (oxotremorine) and P1 (adenosine) receptor agonists are effective inhibitors of transmission, whereas xylazine surprisingly has no effect.