Dopamine produces forearm vasodilatation following alpha-adrenoceptor blockade by an action on vascular dopamine (DA1) receptors in man.

The purpose of this study was to investigate the receptor type mediating dopamine-induced forearm vasodilatation following alpha-adrenoceptor blockade. Forearm blood flow (FBF) was measured using venous occlusion plethysmography in normal volunteers. Intra-arterial (i.a.) dopamine alone produced variable and small changes in FBF. However, following alpha-adrenoceptor blockade with phenoxybenzamine, dopamine infusion resulted in forearm vasodilatation in the infused arm. This effect was not antagonized by the beta-adrenoceptor antagonist propranolol, but was antagonized by the vascular dopamine receptor antagonist, sulpiride, the (d) enantiomer being more active than the (l). It is concluded that i.a. dopamine induces forearm vasodilatation following alpha-adrenoceptor blockade by an action on vascular dopamine (DA1) receptors similar to those described in the renal and mesenteric vasculature of other species.