Effect of quinpirole on neurogenic vasoconstriction in the in situ autoperfused hindquarters and renal vascular beds of the rat.

1. The effects of local administration of quinpirole were studied in the in situ autoperfused hindquarters and renal vascular beds, in order to assess whether presynaptic dopamine receptors in these vascular systems could play a role in the hypotensive effect of this agonist. 2. In both preparations, local injection of quinpirole did not alter perfusion pressure, but reduced the pressor response to electrical stimulation of the sympathetic innervation. Increases in perfusion induced by local administration of noradrenaline were not altered by quinpirole. 3. The inhibitory effect of quinpirole on the stimulation-evoked pressor responses was completely antagonized by intravenous administration of the DA2-receptor antagonist domperidone (0.5 mg kg-1) but not by the DA1-receptor antagonist SCH 23390 (0.3 mg kg-1) or the alpha 2-adrenoceptor antagonist idazoxan (0.3 mg kg-1). 4. The results indicate that quinpirole inhibits neurally induced pressor responses in the autoperfused hindquarters and renal vascular beds of the rat by stimulation of presynaptic dopamine receptors. These receptors may be involved in the hypotensive action of quinpirole in the rat.