Continuous intravenous infusion of LY171555, a potent selective D2 receptor agonist, lowers blood pressure in the conscious rat.

Cardiovascular responses to sustained infusion of quinpirole (LY171555), a dopamine (DA) D2 receptor agonist, and bolus injection of quinpirole following sustained infusion were examined in conscious, unrestrained Sprague-Dawley rats to investigate the contributions of central and peripheral D2 receptors to the regulation of cardiovascular function. Continuous intravenous administration of quinpirole induced a transient pressor response followed by normalization of mean arterial pressure (MAP) and, at higher doses, a decrease in MAP below control levels. Intravenous bolus injections of quinpirole administered 30 min after termination of the infusion produced dose-dependent depressor responses which were blocked by pretreatment with domperidone, a peripheral D2 antagonist. The data suggest that continuous intravenous administration of quinpirole produces a transient centrally mediated pressor effect which is followed by a more sustained, peripherally mediated depressor response.