Effects of 6-hydroxydopamine on dopamine and noradrenaline content in dog blood vessels and heart. Evidence for a noradrenaline-independent dopamine pool.

The noradrenaline and dopamine depletion induced by 6-hydroxydopamine (6-OHDA) and pargyline plus 6-OHDA was investigated in the heart, mesenteric, renal, splenic and femoral arteries and saphenous vein of the dog. Catecholamine concentrations in plasma were also analyzed in these two experimental conditions. 6-OHDA and pargyline plus 6-OHDA induced a parallel decrease of the noradrenaline and dopamine content in the main trunk of the mesenteric artery, femoral artery and heart. In the proximal branches of the mesenteric artery, renal and splenic arteries 6-OHDA selectively reduced noradrenaline (by 50%) without changes in dopamine levels. Previous treatment with pargyline abolished this selectivity and depleted the tissue levels of both noradrenaline and dopamine by 75%. The noradrenaline and dopamine levels in the saphenous vein were not significantly reduced by 6-OHDA (15%) and pargyline plus 6-OHDA (40%). 6-OHDA and pargyline plus 6-OHDA increased both noradrenaline and adrenaline concentrations in plasma, without significant changes in dopamine concentrations. The present findings suggest: an independent dopamine presence in the proximal branches of the mesenteric artery, renal artery and splenic artery; that noradrenaline and dopamine are in one and the same structure in the heart, femoral artery and the main trunk of the mesenteric artery; the saphenous vein is more resistant to chemical sympathectomy than arterial blood vessels; the changes in plasma catecholamine concentrations are probably related to a compensatory mechanism initiated at the adrenal medulla.