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

Abstract

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-[¹⁴C]-arginine to L-[¹⁴C]-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.

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