Calcium‐independent NO‐synthase activity and nitrites/nitrates production in transient focal cerebral ischaemia in mice

1 The temporal changes in constitutive NO‐synthase (cNOS) and in calcium‐independent NO‐synthase activities were studied in mice subjected to 2 h of transient focal cerebral ischaemia. The changes in brain nitrites/nitrates (NO x ) content were also studied. 2 NOS activities were measured by the conversion of L ‐[ 14 C]‐arginine to L ‐[ 14 C]‐citrulline. Brain NO x contents were investigated by the Griess colourimetric method. 3 cNOS activity in the infarcted cortical area was significantly reduced after 6 h of reperfusion and this activity remained attenuated for up to 10 days after ischaemia. A calcium‐independent NOS activity began to increase 48 h after reperfusion, reached a maximum at 7 days and returned to baseline at 10 days. 4 There was a significant increase of brain NO x content beginning after 3 days of reperfusion. This increase was maximal at 7 days and returned to baseline at 10 days. 5 Thus, ischaemia followed by recirculation leads to a rapid, prolonged drop in cNOS activity in the infarcted cortex. There is also a substantial appearance of calcium‐independent NOS activity in the later phase of transient ischaemia, leading to an important increase of NO x production.British Journal of Pharmacology (1997) 122 , 625–630; doi: 10.1038/sj.bjp.0701427