Sympathomimetic actions of reserpine administered during treatment with dopamine in the dog

Reserpine injected intravenously during infusion with dopamine brought about sympathomimetic effects, but a second injection of reserpine after 120 minutes did not elicit such effects. This pressor effect was eliminated by phenoxybenzamine and this positive chronotrpic effect by propranolol. Reserpine induced similar but weak sympathomimetic effects after cocaine, while it induced no changes in blood pressure and heart rate after infusion with noradrenaline. Meanwhile, pressor response to dopamine was potentiated 24 hours after reserpine and was further potentiated after additional infusion with noradrenaline. The sympathomimetic actions induced by the concurrent administration of reserpine and dopamine may be attributable to a facilitation of those indirect mechanisms, prinicpally of endogenous catecholamine release.