Submitted on May 3, 2004
Accepted on October 5, 2004
Exogenous nitric oxide suppresses flow-induced endothelium-derived nitric oxide production due to depletion of tetrahydrobiopterin
Seiichi Mochizuki1*, Pieter Sipkema1, Masami Goto1, Osamu Hiramatsu1, Hiroshi Nakamoto1, Eiji Toyota1, Tatsuya Kajita1, Fumiyuki Shigeto1, Toyotaka Yada1, Yasuo Ogasawara1, and Fumihiko Kajiya1
1 Department of Medical Engineering, Kawasaki Medical School, Kurashiki, Japan
* To whom correspondence should be addressed. E-mail: mochi{at}me.kawasaki-m.ac.jp.
Exogenous nitric oxide (NO) suppresses endothelium-derived NO production. We were interested if this is also the case in flow-induced endothelium-derived NO production. And if so, is the mechanism due to intracellular depletion of tetrahydrobiopterin (BH4; a cofactor of NO synthase: NOS), which results in superoxide production by uncoupled NOS? Isolated canine femoral arteries were perfused with 100 µM S-nitroso-N-acetylpenicillamine (SNAP; an NO donor) and/or 64 µM BH4. Perfusion of SNAP suppressed flow-induced NO production, evaluated as a change in the slope of the linear relationship between perfusion rate and NO production rate (P < 0.02 vs. control; n=7). Subsequent BH4 perfusion returned the slope to the control level. Concomitant perfusion of SNAP and BH4 retained the control-level NO production (n = 7). Concomitant perfusion of SNAP and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; 1 mM; a membrane-permeable superoxide scavenger) also retained the control-level NO production (n = 7), while perfusion of Tiron after SNAP could not return the NO production to the control level (P < 0.02 vs. control; n = 7). We also found a significant decrease in BH4 concentration in the endothelial cells after SNAP perfusion. In conclusion, these results indicate that exogenous NO suppresses the flow-induced endothelium-derived NO production by superoxide released from uncoupled NOS due to intracellular BH4 depletion.
