Vasoactive drugs could alter the fluid restitution from the tissue and redistribute blood volume between the macrocirculation and microcirculation.Methods and ResultsWith bolus injections of vasoactive drugs in anesthetized rabbits, we measured the changes in blood and plasma density for the determination of the volume of restitution and redistribution. Epinephrine 3.5, μg/kg caused a fluid loss to the tissue, leading to a transient decrease in total blood volume by 2.30 mL/kg. Because of blood volume redistribution, the peak volume reduction was accompanied by a volume reduction of 0.81 mL/kg from the macrocirculation and 1.49 mL/kg from the microcirculation. Phenylephrine 70 μg/kg caused a peak reduction in total blood volume of 1.40 mbVkg (with 0.41 mL/kg from macrocirculation and 0.99 mb/kg from microcirculation). Nitroprusside 7 μg/kg increased the blood volume by 1.44 mL/kg (0.83 mb/kg macro and 0.61 mb/kg micro), nitroglycerin 7 μg/kg by 1.48 mL/kg (0.97 mL/kg macro and 0.51 mL/kg micro), and isoproterenol 7 μg/kg by 2.07 mL/kg (0.68 mL/kg macro and 1.39 mL/kg micro). All plasma (or blood) density changes measured for the five drugs (with epinephrine, phenylephrine, and nitroprusside done over a wide dosage range) correlated linearly with the drug-induced changes in arterial pressures.ConclusionsThese results indicate that vasoactive drugs alter total blood volume and the volume of microcirculation and macrocirculation.