Role of nitric oxide during the initial phase of reperfusion after retinal ischemia in the rat

The onset of reperfusion and the recovery of the ERG b-wave following retinal ischemia was examined among three groups of rats: group 1 (n = 12) and group 2 (n = 6) received pretreatment with NG-nitro-L-arginine (20 mg/kg, i.p., 2 h before ischemia) followed by intravenous injection of saline (group 1) or of 200 mg/kg L-arginine (group 2) 5 min before the end of ischemia; group 3 (n = 7) received saline pretreatment followed by intravenous injection of saline as a control. Group 1 showed delayed onset of reperfusion compared to the other two groups and a reduction in the rate of the b-wave recovery compared to the control on the 1st day after reperfusion (group 1 vs. group 3; p = 0.0357). The L-arginine posttreatment significantly increased the b-wave recovery (group 2 vs. group 1; p = 0.0005 on day 1 and p < 0.0006 on day 3). The rate of the b-wave recovery in group 1 was inversely proportional to the time to establish complete reperfusion. Inhibition of nitric oxide synthase during the initial phase of reperfusion may worsen the recovery of the b-wave following retinal ischemia, at least in part, by inhibiting establishment of reperfusion.