The vasocontractive action of norepinephrine and serotonin in deep arterioles of rat cerebral gray matter

TaKAHASHI, R., SAKAI, T., FURUYAMA, Y., KONDO, Y., INOUE, C.N., ONUMA, S. and IINUMA, K. The Vasocontractive Action of Norepinephrine and Serotonin in Deep Arterioles of Rat Cerebral Gray Matter. Tohoku J. Exp. Med., 2000, 190 (2), 129-142- To examine the direct effects of norepinephrine (NE) and serotonin (5-HT) on the contractility of arterioles in the gray matter of the rat cerebrum, me micro-perfused arterioles in vitro and observed the changes in luminal diameter under the stop- flom condition with constant intraluminal pressure, While the average diameter of the lumen of arterioles was 39.9+/-9.7 mu m (n=7) in Hepes-buffered saline, the average in 10(-7) M NE in the extraluminal solution changed into smaller in saline by 21.1+/-5.4% (n=7). The contractile effect of NE shows a dose-dependent curve between the 10(-7) and 10(-5) M. The contractile response to 10(-6) M NE was significantly reduced by yohinbin, an alpha(2) blocker. 10(-6) M NE applied to the lumen also caused contraction of arterioles by 12.4+/-5.3% in diameter (n=5). 5-HT at 10(-7) M in the extraluminal solution caused contraction of arterioles by 10.9+4.4% in diameter (n=7). 5-HT in the extraluminal solution caused contraction of arterioles in a dose dependent manner between 10(-10) and 10(-6) M. The contractile effect of 5-HT at 10(-6) M was strongly reduced by 10(-6) M ketanserin, a 5-HT2 receptor antagonist. 5-HT applied to the lumen had no effect at all ( n=6), however NE applied to the lumen caused contraction. These results strongly suggest that 5-HT plays a significant role in arteriolar contractility only from the cerebrospinal fluid (CSF) side, while NE is an important regulator of arteriolar contractility from both the CSF and blood circulation sides. - norepinephrine; serotonin; cerebral blood flow; in vitro microperfusion; vasocontraction (C) 2000 Tohoku University Medical Press.