Changes in regional blood flow distribution induced by infusions of dopexamine hydrochloride or dobutamine in anesthetized dogs.

Systemic blood flow distribution was determined using radionuclide-labeled microspheres in anesthetized dogs during infusions of dopexamine hydrochloride or dobutamine. Three doses of the drugs were administered intravenously, in the form of 22-minute infusions (3 X 10(-9), 10(-8), 3 X 10(-8) mol/kg/min [1.3 to 12.9 micrograms/kg/min] dopexamine hydrochloride and 10(-8), 3 X 10(-8), 10(-7) mol/kg/min [3.4 to 34.0 micrograms/kg/min] dobutamine). Both drugs induced dose-dependent acceleration of the heart rate. Blood pressure was maintained during infusions of dobutamine, while dopexamine hydrochloride induced arterial hypotension. As a result, the increments in heart rate-blood pressure product were smaller with dopexamine hydrochloride than with dobutamine. Dopexamine hydrochloride induced blood flow increments in the heart, several sections of the gastrointestinal tract, kidney and skeletal muscle. Quantitatively, these changes were different from those induced by dobutamine in only 3 organs. The myocardial blood flow increments during infusions of dopexamine hydrochloride were smaller than those of dobutamine, whereas in the stomach and in skeletal muscle, the flow increments induced by dopexamine hydrochloride were significantly greater than those induced by dobutamine. The findings suggest that dopexamine hydrochloride, by virtue of its agonist activity at beta 2-adrenergic and DA1- and DA2-dopaminergic receptors, is a powerful vasodilator.