Influence of adenosine on responses to vagal nerve stimulation in the anesthetized rabbit

The influence of local adenosine infusion into the celiac artery on the gastric contractile responses to centrifugal vagal nerve stimulation was studied in anesthetized rabbits, and was compared with the effects of systemic administration of equivalent amounts of adenosine. Close arterial infusion of adenosine caused a marked reduction of gastric contractions induced by nerve stimulation, whereas corresponding responses to close arterial infusions of acetylcholine were enhanced during adenosine. The comparison with systemic adenosine administration revealed that the influence on gastric neurotransmission was not related to the hypotensive effect of the compound. No effects of adenosine were seen on bronchial activity as measured by insufflation pressure. Variable effects were obtained on cardiac responses to vagal stimulation. Gastric smooth muscle contractions elicited in vitro by transmural nerve stimulation were affected by adenosine in a biphasic manner, initial inhibition followed by potentiation of the apparently cholinergic responses. It is suggested that adenosine may modulate cholinergic neurotransmission in vivo by a dual effect, prejunctional inhibition and postjunctional enhancement.