Unoprostone activates FP receptors (EC 50 = 4.12 µM), a metabolite of the eye pressure-lowering drug unoprostone isopropyl ester. It's derived from this ester via hydrolysis. In rats, intravitreal unoprostone (1.2, 3.6, or 6 µg/µl) halts constant light-caused photoreceptor decay.