Nitric oxide induces vascular permeability changes in the guinea pig conjunctiva

The role of nitric oxide (NO) as an inflammatory mediator in the mechanism of increased microvascular permeability was examined in a guinea pig model of allergic conjunctivitis. Topical challenge with antigen, compound 48/80, histamine or platelet activating factor (PAF) resulted in a marked increase of the conjunctival vascular permeability. Vascular permeability was determined by measuring the albumin content in the lavage fluid of the challenged eyes after 30 min. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) eyedrops caused a significant inhibition of the clinical score and the vascular permeability after challenge with either antigen, histamine or PAF. Aminoguanidine prophylaxis also resulted in a significant inhibition of both the clinical score and vascular permeability in response to all the used provocative agents except PAF. Our observations indicate that NO is an important factor in the induction of the vascular permeability provoked by histamine but seems to play no role in the mechanism by which PAF exerts increased vascular permeability in the conjunctiva.