The EP₂ receptor is the predominant prostanoid receptor in the human ciliary muscle

Prostaglandins can reduce intraocular pressure by increasing uveoscleral outflow. We have previously demonstrated that the human ciliary muscle was a zone of concentration for binding sites (receptors) for prostaglandin F ₂α and for prostaglandin E₂. Here, we try to elucidate the types of prostanoid receptors in the ciliary muscle using competitive ligand binding studies in human eye sections and computer assisted autoradiographic densitometry. Saturation binding curves showed that the human ciliary muscle had a large number of binding sites with a high affinity for prostaglandin E₂compared with prostaglandin D₂ and F ₂,. The binding of tritiated prostaglandin E₂ and F ₂α in the ciliary muscle was displaced most effectively by prostaglandin E₂ and 11- deoxy prostaglandin E₁ (a selective EP₂ prostanoid receptor agonist), whereas the binding of prostaglandin D₂ was displaced most effectively by prostaglandin E₂ and D₂. These results indicate that the dominant prostanoid receptor in the human ciliary muscle is the EP₂ subclass and that there is also a small number of DP receptors.