Biphasic responsiveness of rat pial arterioles to dopamine: direct observations on the microcirculation.

The effects of local perivascular application of dopamine to rat pial arterioles. (20-40 micrometer i.d.) were examined in situ, at the microcirculatory level, by use of a high-resolution closed circuit television microscope recording system. Local application of very low, physiological doses (1 to 10 pg) of dopamine to pial arterioles of the anaesthetized rat induces vasodilatation, whereas higher doses induce vasoconstriction. The magnitudes of these biphasic responses obtained in male rats were not significantly different from those obtained in female animals. Our findings support the theory that local release of this neurotransmitter amine from perivascular cells in the brain may promote local increases in cerebral blood flow.