Studies on prostanoid receptors in ocular tissues

Cyclooxygenase products of arachidonic acid, for example prostaglandins (PGs), prostacyclin, and thromboxane A2, mediate a wide range of physiological actions. Vasodilation, increased vascular permeability, platelet aggregation and its inhibition, and immunomodulation are some of the important biological actions of cyclooxygenase products (1). Depending on type and dose, PGs cause vasodilation, increase or decrease intraocular pressure, and disrupt the blood-aqueous barrier (2, 3). These actions also vary qualitatively and quantitatively with the animal species. Prostaglandins, like any biological molecule, must act by binding with their specific receptors. Coleman and coworkers (4, 5), from a series of studies with PG agonists and antagonists in vascular and non-vascular smooth muscle preparations, classified PG receptors. This classification led to a greater appreciation of the relationship between PG actions and specific PG receptors in various tissues. Ocular actions of PGs linked with specific PG receptors are far from being clear. In this communication we will review our work on PG binding sites in ocular tissues and PG receptors coupled to adenylyl cyclase or phosphoinositidase C signal transduction pathways in ocular tissues of various animal species.