GANGLIONIC DOPAMINE RECEPTORS AS MEDIATORS OF THE INHIBITION OF NEUROGENIC VASOCONSTRICTION PRODUCED BY FENOLDOPAM

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Abstract
We have performed experiments to study the action of fenoldopam, a DA1 receptor agonist, on neurogenic vasoconstriction elicited during preganglionic sympathetic nerve stimulation. Infusion of fenoldopam to anaesthetized dogs decreased mean blood pressure and caused significant impairment of hindlimb vasoconstriction produced by preganglionic lumbar sympathetic nerve stimulation. The inhibitory action of fenoldopam on neurogenic vasoconstriction was antagonized by R-sulpiride but not by SCH-23390. However, SCH-23390 was more effective than R-sulpiride in antagonizing the hypotensive action of fenoldopam. These results demonstrate that fenoldopam produces inhibition of vascular sympathetic neurotransmission by activating dopamine receptors located at sympathetic ganglia, and this receptor may not be similar to the vascular DA1 receptor.