Pilocarpine Antagonizes Prostaglandin F2α-Induced Ocular Hypotension in Monkeys

Abstract

• Twice daily topical application of 50 μg of prostaglandin F_2αtromethamine to cynomolgus monkey eyes produced significant ocular hypotension lasting at least six hours, with the intraocular pressure (IOP) falling between 35% and 50%, ie, to about 8 to 10 mm Hg, following the seventh dose. A single topical application of 1 mg of pilocarpine hydrochloride produced a much smaller IOP reduction and strong, probably maximal accommodation, both of which lasted at least eight hours. When prostaglandin F_2α-treated eyes were given pilocarpine before the seventh dose of prostaglandin F_2α, accommodation and IOP responded as in eyes receiving pilocarpine only. Atropine sulfate pretreatment of eyes receiving pilocarpine and prostaglandin F_2αcompletely prevented pilocarpine-induced accommodation and inhibition of ocular hypotension induced by prostaglandin F_2α. We hypothesize that (1) prostaglandin F_2αreduces IOP by increasing uveoscleral drainage of aqueous humor, and (2) pilocarpine pretreatment contracts the ciliary muscle, obliterating the intramuscular spaces and closing off the uveoscleral drainage pathway and thus physiologically blocking the effect.