Middle ear effusion induced by various inflammatory mediators and neuropeptides. An experimental study in the rat

Vascular leakage in the middle ear cavity was studied after i.v. administration of various substances in rats and determined by the Evans blue technique. Bradykinin, histamine, serotonin, acetylcholine, substance P (SP) and vasoactive intestinal polypeptide (VIP) resulted in extravasation of Evans blue. In the case of bradykinin and histamine, the leakage was dose dependent. Calcitonin gene-related peptide (CGRP) did not affect vessel permeability. In other experiments the effect of histamine antagonists was tested on production of middle ear effusion, caused by blowing air at 14 degrees C into the external auditory canal (EAC). The increase in vessel permeability in this otitis media model was inhibited by the H2-receptor antagonist cimetidine, at doses 0.1 and 1.0 mg/ml. Diphenhydramine, an H1-receptor antagonist, arrested only partly middle ear fluid accumulation. Our study demonstrated that various inflammatory mediators and neuropeptides are capable of inducing vascular leakage in the middle ear cavity. It was also concluded that H2-receptors are involved in the regulation of middle ear vascular permeability.