<P> The LD, or dose which is expected to prove lethal in 50% of the population, has been found to be: 59 mg / kg (mouse; administered intravenously); 950 mg / kg (mouse; administered intraperitoneally); 163 mg / kg (rat; administered intraperitoneally); 79 mg / kg (dog; administered intravenously). </P> <P> If extravasation occurs local tissue death may result . The medication phentolamine can be injected at the site to try to decrease the risk of tissue death . </P> <P> Its effects, depending on dosage, include an increase in sodium excretion by the kidneys, an increase in urine output, an increase in heart rate, and an increase in blood pressure . At low doses it acts through the sympathetic nervous system to increase heart muscle contraction force and heart rate, thereby increasing cardiac output and blood pressure . Higher doses also cause vasoconstriction that further increases blood pressure . </P> <P> While some effects result from stimulation of dopamine receptors, the prominent cardiovascular effects result from dopamine acting at α, β, and β adrenergic receptors . </P>

What is the mechanism of action of dopamine
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