Effects of etomidate, propofol and thiopental anaesthesia on arteriolar tone in the rat diaphragm

We have assessed, by intravital microscopy in rats, the effects of different anaesthetics on diaphragmatic arteriolar diameter. Rats were anaesthetized with etomidate, propofol or thiopental (groups E, P and T, respectively) and the diameters of the arterioles were measured sequentially at baseline and after topical application of either mefenamic acid (MA, 20 mumol litre-1) or N omega-nitro-L-arginine (NNA, 300 mumol litre-1), inhibitors of prostaglandins and nitric oxide, respectively. In group E, baseline arteriolar diameters were significantly higher than those in the two other groups (P < 0.01). MA and NNA induced significant constriction in the three groups (P < 0.001). However, whereas constriction induced by NNA was similar in the three groups, constriction induced by MA was significantly higher in group E compared with groups P and T (P < 0.05). We conclude that diaphragmatic arteriolar diameters in rats were greater during etomidate than during thiopental or propofol anaesthesia. This phenomenon may be mediated by prostaglandins.