Effects of dobutamine on brain surface microvessels in rats

The effects of dobutamine on the diameters of rat pial vessels were investigated in vivo using a closed cranial window technique. Dobutamine (10(-7)-10(-3) M) was dissolved in artificial cerebrospinal fluid (CSF). Arterioles (17-78 microns in diameter) and venules (20-97 microns in diameter) were observed through the cranial window over the left parietal cortex. Superfusion of the brain surface with only artificial CSF had no effect on vessel diameter. Dobutamine, even at a high concentration of 10(-4) M, did not induce significant diameter changes in the pial vessels, compared with control animals. The arterioles showed marked dilatation (+73%) during superfusion with 10(-3) M dobutamine (p < 0.01 vs. control). The venules were also dilated (+12%), although the increased diameter was not statistically different from controls. Therefore, dobutamine did not induce a dose-dependent dilation. The results strongly suggest that dobutamine at clinical dosages does not have a direct vasomotor effect on brain microvessels.