Supplementary Material for: Histaminergic H3-Heteroreceptors as a Potential Mediator of Betahistine-Induced Increase in Cochlear Blood Flow

Objective: Betahistine is a histamine-like drug that is considered beneficial in Ménière's disease by increasing cochlear blood flow. Acting as an agonist at the histamine H₁-receptor and as an inverse agonist at the H₃-receptor, these receptors as well as the adrenergic α₂-receptor were investigated for betahistine effects on cochlear blood flow. Materials and Methods: A total of 54 Dunkin-Hartley guinea pigs were randomly assigned to one of nine groups treated with a selection of H₁-, H₃- or α₂-selective agonists and antagonists together with betahistine. Cochlear blood flow and mean arterial pressure were recorded for 3 min before and 15 min after infusion. Results: Blockage of the H₃- or α₂-receptors caused a suppression of betahistine-mediated typical changes in cochlear blood flow or blood pressure. Activation of H₃-receptors caused a drop in cochlear blood flow and blood pressure. H₁-receptors showed no involvement in betahistine-mediated changes of cochlear blood flow. Conclusion: Betahistine most likely affects cochlear blood flow through histaminergic H₃-heteroreceptors.