Table 1. Effect of U50,488H on NO production in serum of HPH rats exposed to chronic hypoxia for 2 wk.

Group	NO(µmol/L)
Control	58.3±2.8
2 w	32.7±2.5 **
2 w+NS	35.2±2.2**
2 w+U50	54.1±2.8 ## §§
2 w+U50+nor-BNI	36.0±2.9ττ
2 w +nor-BNI	36.9±3.4ττ

Values are means ± SE; n = 8. NOx concentration in serum was determined by nitrate enzyme reverting method. 2 w: hypoxia for 2 wk; NS: normal saline; U50: U50,488H; nor-BNI: nor-Binaltorphimine;

^** P<0.05 vs. control;

^## P<0.05 vs. 2 w;

^§§ P<0.05 vs. 2 w+NS;

^ττ P<0.05 vs. 2 w+U50.