A comparison between the pattern of dopamine and noradrenaline release from sympathetic neurones of the dog mesenteric artery.

The release of dopamine and noradrenaline (NA), from the main trunk of the mesenteric artery and its proximal branches elicited by electrical nerve stimulation and K+, has been measured by using high pressure liquid chromatography with electrochemical detection. Both stimuli released dopamine and NA. With the main trunk of the mesenteric artery, dopamine represented 8% of the NA tissue content; the dopamine/NA ratio in the catecholamine overflow caused by nerve stimulation or K+-induced depolarization also averaged 8%. For the proximal branches the tissue dopamine/NA ratio was significantly greater than that observed to occur in the overflow caused by nerve stimulation and K+. When the perifusion with a K+-enriched medium was extended to 120 min the amount of NA released from both the main trunk and the proximal branches progressively declined. The same pattern of release was observed for dopamine in the main trunk, whereas for the proximal branches dopamine overflow did not decline throughout the perifusion period. The addition of alpha-methyl-p-tyrosine did not change the pattern of amine overflow. Our interpretation of these results is that both dopamine and NA are derived from the same sympathetic neurone. In the proximal branches of the mesenteric artery dopamine and NA appear to be in two different storage structures, whereas in the main trunk both dopamine and NA are located in only one storage structure.