RESUMEN
BACKGROUND: Aqueous extract of Pleurotus tuberregium (PT) has been shown to reduce intraocular pressure (IOP) but the underlying mechanism has not been explained. PURPOSE: To investigate the effect of PT on the bovine iris in vitro in comparison with acetylcholine (ACh). METHOD: Strips of the iris were mounted in 10 ml organ baths and exposed to increasing concentrations of PT, ACh and a combination of both agents. The effect of atropine on the responses to the agents was also investigated. RESULTS: PT and ACh separately caused contractile responses on the iris, but their effect reduced with higher concentrations. Combination of PT and ACh did not significantly alter the reduced responses seen with high concentrations of either agent. Atropine completely abolished the contractile responses of the agents. CONCLUSION: The contractile effect of PT on muscarinic receptor-containing iris muscle may explain its IOP reducing property.