Abstract
The present study was performed in order to define the optimum effective dose of dopamine for dogs. Thirty-nine anesthetized healthy mixed-breed dogs were given three different doses of dopamine by infusion (3, 10, or 20μg/kg, min), and regional blood flow was measured using colored microspheres in the brain, heart, kidneys, stomach, intestines, liver, and lungs. Blood flow in the brain was maintained unchanged. Blood flow in the heart increased in proportion to the increase in cardiac output, suggesting the need to avoid overloading the cardiac muscle. Blood in the digestive tract moved to the various organs as they required it. Generally speaking, a small dose of dopamine activates dopamine-specific receptors so that renal and coronary arteries expand, a larger dose activates β1-adorenoceptors in the heart so that cardiac output increases, and a still larger dose of dopamine activates α-adorenoceptors in the whole body so that peripheral arteries contract. In our study, the larger the dose, the greater was the activating effect on α-adorenoceptors in all organs. We also found that the effect of dopamine was influenced not only by how it activated these receptors, but also by the autoregulation system of blood flow. Moreover, the group of dogs receiving 10μg/kg/min of dopamine showed a satisfactory increase of renal blood flow, cardiac blood flow and cardiac output. That is, a large dose of dopamine, such as the 10μg/kg/min used in this study, which is larger than usual, was more effective and safer than it was thought. These findings indicated the possibility of raising the upper limit of the dosage in administering dopamine to dogs clinically.
