Dilation of perforating arteries in rat brain in response to systemic hypotension is more sensitive and pronounced than that of pial arterioles: simultaneous visualization of perforating and cortical vessels by in-vivo microangiography.

Autoregulatory responses of perforating arteries play a key role in the maintenance of microcirculation of the deep brain regions. The aim of this study was to test our hypothesis that autoregulatory vasodilatation of perforating arteries is more effective than that of cortical arteries. We performed cerebral microangiography in adult Wistar rats using monochromatic synchrotron radiation at SPring-8 and for the first time radiographically visualized perforating arteries and cortical arteries simultaneously in a single view. In response to hypotension induced by arterial bleeding, both arteries showed significant vasodilatation. Steady-state responses of increments in caliber to stepwise hypotension revealed that perforating arteries exhibited significant vasodilatation at blood pressure below 80-99 mm Hg. Cortical arteries, on the other hand, showed a gradual and smaller vasodilatation beginning at 60-79 mm Hg. For the lowest blood pressure range at 40-59 mm Hg, the smallest arteries with a diameter of 20-40 microm showed maximal dilation in both groups, but perforating arteries showed significantly larger dilatation (185.0% of baseline diameter) than cortical arteries (152.7%; P=0.003). Our results indicate that vasodilatation of perforating arteries is more sensitive and pronounced in response to systemic hypotension than that of pial arteries, which explains how cerebral microcirculation is maintained efficiently in the deep brain regions.