Human vasodilator responses to a dopamine agonist: possible mechanisms

The action of fenoldopam, a selective dopamine DA1 agonist, on resting forearm blood flow was studied in healthy male volunteers by venous plethysmography. Metoclopramide and (+/-) sulpiride were used as dopamine antagonists. Intra-arterial fenoldopam over the range (100 ng/min to 1 microgram/min) produced a dose-related increase in forearm blood flow without evidence of systemic effects. The response to fenoldopam was not antagonized by metoclopramide or (+/-) sulpiride and neither antagonist alone altered resting forearm blood flow. It is unclear whether the effects of fenoldopam in the forearm vasculature are mediated through the vascular dopamine receptor.