Evidence for a non-precursor dopamine pool in noradrenergic neurones of the dog mesenteric artery.

The effects of dopamine beta-hydroxylase inhibition by disulfiram on dopamine and noradrenaline concentrations were investigated at various times in the main trunk and proximal branches of the dog mesenteric artery. The effects of desmethylimipramine and benztropine on the uptake of exogenous dopamine in the proximal branches of the mesenteric artery were also analyzed. The rate constant of dopamine accumulation after dopamine beta-hydroxylase inhibition in the main trunk (0.1137 h-1) was significantly higher than that observed in the proximal branches (0.075 h-1). The rate constants of noradrenaline decline were similar in both segments of the mesenteric artery (about 0.052 h-1). The uptake of exogenous dopamine in the proximal branches of the mesenteric artery was insensitive to benztropine and only blocked by desmethylimipramine. These results suggest the existence of a non-precursor dopamine pool in noradrenergic neurones supplying the proximal branches of the dog mesenteric artery, and also provide evidence in favour of the absence of independent dopaminergic neurones in this vascular area.