Anaesthetic agents decrease the activity of nitric oxide synthase from human polymorphonuclear leucocytes

Nitric oxide (NO) inhibitors reduce the threshold for anaesthesia. We haveinvestigated the action of anaesthetic agents on human nitric oxidesynthase (NOS) activity. Thiopentone reduced mean NOS activity to 36.6 (SD8.9) % of control at 100 mumol litre-1 (P < 0.001) and 50.9 (20.3) % at1 mmol litre-1 (P < 0.05). Ketamine showed similar effects, withactivity reduced to 67.0 (17.6) % (P < 0.05) and 57.7 (8.5) % (P <0.001) at 100 mumol litre-1 and 1 mmol litre-1, respectively. Etomidate 100mumol litre-1 did not significantly alter activity (88.2 (8.1) %) but 1mmol litre-1 did (60.6 (10.4) %, P < 0.005). Halothane also caused asignificant decrease in NOS activity at all concentrations. This effect wasspecific as other enzymes were unaffected. We conclude that anaestheticagents have a profound effect on NOS activity and as inhibition of NOrelease augments anaesthesia, we suggest that this may play a role in themechanism of anaesthesia in humans.