The present invention is directed to a method of altering the amount or composition of synovial fluids secreted from joints in a subject in need of such treatment. The method comprises administering to a subject a pharmaceutical composition comprising a P2Y purinergic receptor agonist in an amount effective to alter the amount or composition of synovial fluids. The P2Y purinergic receptor agonist is administered in an amount effective to stimulate secretion of synovial fluid, lubricin, hyaluronic acid, or surface-active phospholipids; to enhance joint lubrication; or to treat osteoarthritis. The pharmaceutical compositions useful in the present invention comprise a P2Y purinergic receptor agonist of Formula I and include, but are not limited to: uridine-, adenosine-, cytidine-5'-di- or triphosphates, dinucleoside polyphosphates, and analogs thereof. The invention is useful for treating conditions associated with reduced joint lubrication and joint stiffness, such as osteoarthritis.