NITRIC-OXIDE INDUCES VASCULAR-PERMEABILITY CHANGES IN THE GUINEA-PIG CONJUNCTIVA

The role of nitric oxide (NO) as an inflammatory mediator in the mecha nism 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. Vascu lar permeability was determined by measuring the albumin content in th e lavage fluid of the challenged eyes after 30 min. Pretreatment with N-G-nitro-L-arginine methyl ester (L-NAME) eyedrops caused a significa nt inhibition of the clinical score and the vascular permeability afte r challenge with either antigen, histamine or PAF. Aminoguanidine prop hylaxis also resulted in a significant inhibition of both the clinical score and vascular permeability in response to all the used provocati ve agents except PAF. Our observations indicate that NO is an importan t factor in the induction of the vascular permeability provoked by his tamine but seems to play no role in the mechanism by which PAF exerts increased vascular permeability in the conjunctiva.