Role of the basilar artery in regulation of blood flow to the brain stem in rats.

Large arteries contribute to the regulation of cerebral blood flow. The goal of this study was to examine the effects of changes in diameter of the basilar artery on blood flow to the brain stem. We measured blood flow with laser-Doppler flowmetry in anesthetized rats. The topical application of 10(-6) M serotonin, which selectively constricts large arteries, reduced diameter of the basilar artery by 47 +/- 5% (mean +/- SEM, n = 6) but did not alter blood flow to the ventral brain stem (change in blood flow -2 +/- 5%). The topical application of 10(-8) M vasopressin, which affects both large and small vessels, decreased blood flow by 33 +/- 4% (n = 6). In rats with spontaneous vasomotion, the basilar artery showed rhythmic changes in diameter at a frequency of 4.0 +/- 0.1 cycles/min and an amplitude of 20 +/- 1% of mean diameter (n = 6). Blood flow to the ventral brain stem cycled at the same frequency as and in phase with changes in diameter of the basilar artery, with an amplitude of 15 +/- 1%. We conclude that constriction of the basilar artery may occur with no change in brain stem perfusion. The distinct changes in blood flow during spontaneous vasomotion suggest that vasomotion occurs in intraparenchymal arterioles as well as in the basilar artery.