Dopamine released from nerve terminals activates prejunctional dopamine receptors in dog mesenteric arterial vessels

The fractional release of dopamine and noradrenaline (NA) from the main trunk of the dog mesenteric artery and its proximal branches, when elicited by K+ (52 mM), was measured by high pressure liquid chromatography with electrochemical detection. K+-induced depolarization released both dopamine and NA. For the main trunk of the mesenteric artery, the fractional release of dopamine and NA were of the same order of magnitude, whereas for the proximal branches dopamine fractional release was significantly lower than that of NA. Phentolamine (0.2 microM) significantly increased dopamine and NA release in both segments of the mesenteric artery. However, for the proximal branches the effect of phentolamine on dopamine and NA release was greater than that observed in the main trunk. Sulpiride (1 microM) significantly increased dopamine and NA release in the proximal branches of the mesenteric artery, whereas in the main trunk sulpiride did not increase amine release. In the proximal branches of the mesenteric artery, sulpiride significantly enhanced dopamine and NA fractional release even after it had been augmented by phentolamine. Apomorphine (0.3 microM) significantly reduced dopamine and NA release in both segments of the mesenteric artery under study; this effect was abolished by sulpiride but not by phentolamine. These results suggest that dopamine and NA released during depolarization by K+ activate prejunctional dopamine and alpha-adrenoceptors, respectively, thereby playing a role in the control of transmitter release.