Submitted on October 30, 2006
Accepted on May 17, 2007
High oxygen tension constricts epineurial arterioles of the rat sciatic nerve via reactive oxygen species
Noriko Sakai1, Risuke Mizuno1, Nobuyuki Ono2, Hiroyuki Kato3, and Toshio Ohhashi1*
1 Department of Physiology, Shinshu University School of Medicine, Matsumoto, Nagano, Japan
2 Department of Electronics and Control Engineering, Nagano National College of Technology, Nagano, Nagano, Japan
3 Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Nagano, Japan
* To whom correspondence should be addressed. E-mail: ohhashi{at}sch.md.shinshu-u.ac.jp.
Microcirculation of the sheath in rat sciatic nerve fiber was investigated by using an intra-vital microscope and changes in the diameter of the epineurial arterioles in response to high-oxygenated Krebs-bicarbonate solution were evaluated. Superfusion with low (0 %) oxygen Krebs-bicarbonate solution (LKS) onto rat sciatic nerves did not affect changes in the diameter of the arterioles. Nifedipine, a Ca2+ channel blocker, caused a dose-dependent dilation of the epineurial arterioles in the condition of LKS. In contrast, superfusion with high (21 %) oxygen Krebs-bicarbonate solution (HKS) onto rat sciatic nerves significantly constricted the epineurial arterioles time-dependently. The HKS-induced constriction of the epineurial arterioles was significantly reduced by the treatment with 120 U/ml superoxide dismutase (SOD) alone or 5000 U/ml catalase alone. In the presence of 120 U/ml SOD plus 5000 U/ml catalase, 10-4 M tempol, 10-6 M diphenyleneiodium (DPI), 2x10-4 M apocynin or 10-6 M allopurinol, the HKS-induced constriction of the epineurial arterioles was completely disappeared. These results suggest that superfusion with high-oxygenated solution onto rat sciatic nerves constricts the epineurial arterioles through ROS (reactive oxygen species) including superoxide and hydrogen peroxide, and that production of superoxide involves NADPH oxidase- or xanthine oxidase-dependent pathway. In conclusion, ROS play significant roles in the regulation of microcirculation of rat sciatic nerves in vivo.
