Role of nitric oxide in the vasodilator but not exudative component of mustard oil-induced inflammation in rat skin.

The participation of nitric oxide (NO) in the neurogenic inflammatory reaction of the rat hindpaw skin to topical application of mustard oil was examined by the use of NG-nitro-L-arginine methyl ester (L-NAME, 43 mumol kg-1 i.v.), an inhibitor of NO formation. Control rats received the same dose of the inactive enantiomer D-NAME. Vasodilatation was recorded by contactless infrared emission thermography, and plasma protein exudation was measured by the Evans Blue leakage technique and by measurement of the paw volume in anaesthetized rats. L-NAME reduced the cutaneous hyperaemia caused by topical administration of mustard oil by about 50% but did not change the exudative reaction to mustard oil. These findings indicate that NO plays a mediator role in the vasodilator component of neurogenic inflammation in the rat paw skin, whereas the increase in vascular permeability does not appear to depend on NO.