The effect of prostaglandin F2 alpha-1-isopropylester (PGF2 alpha-IE) on uveoscleral outflow.

These studies assessed the acute effects of a single dose of prostaglandin F2 alpha-1-isopropylester (PGF2 alpha-IE) on the IOP and AHF, as well as on conventional and uveoscleral outflow, in cynomolgus monkeys. The AHF was determined by a dilution method, using radioactive albumin as a marker. Arterial blood samples were collected and analyzed for radioactivity to determine the flow of aqueous humor to blood, corresponding to the conventional outflow. The uveoscleral outflow was calculated as the difference between the measured AHF and the conventional outflow. Topical application of PGF2 alpha-IE (1 microgram free acid equivalents) to eyes of cynomolgus monkeys caused a small initial increase in IOP followed by a gradual decrease, which was greatest (2.9 +/- 0.6 mmHg below the control eye) at about three hours after the PG application. The mean AHF during 4 hours was slightly higher in the experimental eyes than in the control eyes. The mean uveoscleral outflow during 4 hours was significantly higher in the experimental eyes (0.98 +/- 0.12 microliters.min-1) than in the control eyes (0.61 +/- 0.10 microliters.min-1), while the conventional outflow was significantly lower. The ability of PGF2 alpha-IE to increase the uveoscleral outflow was also demonstrated by autoradiography. These results suggest that PGs exert at least part of their ocular hypotensive effect by increasing the uveoscleral outflow. It remains to be established whether this effect is caused by relaxation of the ciliary muscle or whether other mechanisms, such as structural and metabolic changes, are involved.