Dose-related effects of dopamine on microcirculatory blood flow in resting and active state

We compared the effects of low and high doses of dopamine and dobutamine (a synthetic catecholamine) on blood flow in relaxed or exercising muscles. Experiments were performed on rabbits. Blood flow in the muscles (calf) was estimated with the clearance method of radionuclide 133Xe. Dopamine and dobutamine were infused (iv) in doses of 20 or 40 micrograms/kg/min. Dopamine reduced muscle blood flow in resting state; this effect was more pronounced after higher doses. Dobutamine increased the flow; low doses were less effective. Dopamine may be an important determinant of the distribution of cardiac output to various vascular regions.