Dopamine, 4.0 μg/kg, administered intravenously to conscious dogs, previously instrumented with Doppler ultrasonic or electromagnetic flowmeters, produced biphasic alterations in arterial pressure, heart rate, and superior mesenteric and external iliac resistances. Early increases in arterial pressure, mesenteric and iliac resistances, and decreases in heart rate were followed by directionally opposite changes in these variables. Renal resistance did not rise initially and was decreased for the entire 2 min observation period. Dopamine, 40 μg/kg, produced biphasic alterations in arterial pressure, heart rate, and resistance in all three regional vascular beds. The initial peak increases and later decreases in mesenteric resistance, +181% and 42%, were greater than the early and late changes in renal resistance, +51% and -14%, and in iliac resistance, +97% and -23%. Early vasoconstriction in each of the beds was abolished by alpha adrenergic receptor blockade while late vasodilation persisted after blockade of the alpha and beta adrenergic and of the cholinergic receptors. Regional arterial injection of dopamine, 0.4 μg/kg, before and after autonomic blockades produced alterations in regional resistances qualitatively similar to those observed after 40 μg/kg intravenously. These experiments indicate that in the conscious dog dopamine causes biphasic alterations in resistances which are characterized by early vasoconstriction due to an action on alpha adrenergic receptors and by late vasodilatation due to a specific direct action on dopaminergic receptors in each of these three regional vascular beds. Both the vasoconstrictor and vasodilator actions occurred in all beds studied and were more intense in the mesenteric than in the renal bed.
All Science Journal Classification (ASJC) codes
- Physiology (medical)