controlled air oxygen content (5 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours) then NG-nitroarginine methyl ester (50 mg/kg) (for 0.5 hours) and meclofenamate (3 mg/kg) (for 0.5 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours)

 controlled air oxygen content (21 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours) then NG-nitroarginine methyl ester (50 mg/kg) (for 0.5 hours) and meclofenamate (3 mg/kg) (for 0.5 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours)

 controlled air oxygen content (5 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours) then NG-nitroarginine methyl ester (50 mg/kg) (for 0.5 hours) and meclofenamate (3 mg/kg) (for 0.5 hours)

 controlled air oxygen content (21 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours)

 controlled air oxygen content (5 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours)

 controlled air oxygen content (5 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours)

 controlled air oxygen content (21 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours) then NG-nitroarginine methyl ester (50 mg/kg) (for 0.5 hours) and meclofenamate (3 mg/kg) (for 0.5 hours)

 controlled air oxygen content (21 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours)

 controlled air oxygen content (21 %) (for 28 days) then vehicle control condition (0.15 ml) (for 0.1 hours) then acetylcholine (5 ug/kg/min) (for 0.1 hours) then sodium nitroprusside (5 ug/kg/min) (for 0.1 hours) then NG-nitroarginine methyl ester (50 mg/kg) (for 0.5 hours) then meclofenamate (3 mg/kg) (for 0.5 hours)