Search

Purpose: Activation of prostaglandin (PG)-EP(4) receptors by 3,7-dithiaPGE(1) robustly lowers intraocular pressure in nonhuman primate eyes, which increases outflow facility but has no effect on aqueous secretion or uveoscleral outflow. Because of differences in PG efficacy in outflow function between nonhuman primates and humans, we tested the impact of 3,7-dithiaPGE(1) on conventional outflow function in human donor eyes., Methods: The expression pattern of PG-EP(4) receptors was determined in corneoscleral tissues of human donor eyes and in cultures of human outflow cells by immunofluorescence microscopy and Western blot, respectively. The efficacy of 3,7-dithiaPGE(1) was determined by assaying agonist-stimulated cAMP accumulation and β-arrestin mobilization in cultured human cells. Agonist effects on outflow facility were examined in paired human donor eyes that were perfused at 8 mm Hg of constant pressure, equivalent to 15 mm Hg in vivo., Results: The trabecular meshwork (TM) and Schlemm's canal (SC) cells expressed PG-EP(4) receptors. Agonist-mediated effects on the PG-EP(4) receptors were detected in SC (EC(50) = 6.3 × 10(-9) M, n = 4), but not TM (EC(50) = 1.7 × 10(-7) M, n = 5) cells. Effects in SC cells were blocked by the PG-EP(4) receptor-selective antagonist GW627368 (EC(50) = 1.09 × 10(-2) M, n = 4), but not the PG-EP(2) receptor-selective antagonist AH6809 (EC(50) = 4.10 × 10(-9) M, n = 5). Perfused into human eyes at a concentration that selectively activates PG-EP(4) receptors, 3,7-dithiaPGE(1) (10 nM) increased outflow facility by 51% ± 18% over baseline levels in individual drug-treated eyes after drug exchange (n = 6 eyes; P = 0.05) and by 69% ± 23% (P < 0.01) compared with that in contralateral eyes., Conclusions: Activation of PG-EP(4) receptors expressed by SC cells of the human conventional outflow pathway appears to contribute to PG regulation of outflow facility.

Purpose: As part of a systematic elucidation of the pharmacology of prostaglandin's (PG) effects on intraocular pressure in the monkey, the prototypical selective prostanoid EP(4) receptor agonist (3,7-dithia PGE(1)) was examined. It was found to be highly efficacious in nonhuman primates, and its mechanism of ocular hypotensive activity was investigated., Methods: Intraocular pressure (IOP) was measured by pneumatonometry in conscious monkeys restrained in custom-designed chairs. All other animal experiments were performed in animals sedated with ketamine or anesthetized with ketamine/diazepam and given drug or vehicle for various lengths of time. Aqueous flow was determined by fluorophotometry. Total outflow facility was measured by the two-level, constant-pressure method and by 2-minute tonography in both normotensive and hypertensive monkey eyes. Uveoscleral outflow was measured by perfusing the anterior chamber with FITC-labeled dextran for 30 minutes at a fixed IOP of approximately 15 mm Hg. Isometric responses to drugs were measured in longitudinal and radial preparations of monkey and human isolated ciliary smooth muscle specimens., Results: The selective EP(4) receptor agonist 3,7-dithia PGE(1) and an isopropyl ester prodrug thereof reduced IOP in monkeys. A single dose of 3,7-dithia PGE(1) isopropyl ester, at a 0.01% or 0.1% dose, decreased IOP in the glaucomatous monkey in the range of 40% to 50%. Studies on total outflow facility by the two-level, constant-pressure perfusion method and tonography indicated that EP(4) receptor stimulation facilitated aqueous humor outflow facility. No effect on aqueous flow was apparent. In contrast to all PGs and prostamides studied to date, 3,7-dithia PGE(1) exerted no effect on uveoscleral outflow measured directly. Moreover, it did not relax longitudinal or radial preparations of isolated human or monkey ciliary muscles., Conclusions: The EP(4) receptor agonist 3,7-dithia PGE(1) is a highly efficacious IOP-lowering drug in monkeys. It has no effect on uveoscleral outflow but does increase total outflow facility, which accounts for a substantial proportion of the ocular hypotensive activity.

Purpose: To investigate the ocular hypotensive effect of the prostanoid EP2 receptor agonist butaprost and to establish its mechanism of action., Methods: All experiments were performed in cynomolgus monkeys after topical application of butaprost (0.1%). The effects of butaprost on aqueous humor flow were determined by fluorophotometry. Total outflow facility was measured by the two-level, constant-pressure perfusion method, and uveoscleral outflow was determined by perfusion of FITC-labeled dextran through the anterior chamber. Effects on ocular morphology were studied after tissue fixation with transcardial perfusion by paraformaldehyde and immersion fixation of the globe, in animals subjected to long-term treatment with butaprost. Conscious ocular normotensive monkeys and monkeys with unilateral ocular hypertension were used for intraocular pressure (IOP) studies., Results: Butaprost had no significant effect on aqueous humor flow or total outflow facility in ocular normotensive monkeys. Uveoscleral outflow was significantly higher in the butaprost treated eyes than in vehicle treated eyes, 1.03 +/- 0.20 vs. 0.53 +/- 0.18 microL.min(-1). After a 1-year treatment with butaprost, the morphology of the ciliary muscle was changed, showing increased spaces between ciliary muscle bundles and the apparent formation of new outflow channels. In many instances, changes were observed in the trabecular meshwork as well. Butaprost, in a single 0.1% dose, decreased IOP significantly in ocular normotensive monkeys and reduced IOP in laser-induced glaucomatous monkey eyes to the same level as that in the ocular normotensive contralateral eyes., Conclusions: The prostanoid EP2 receptor agonist butaprost appears to lower IOP by increasing uveoscleral outflow, according to both physiological and morphologic findings. Although the prostanoid EP2 receptor is structurally and functionally distinct from the FP receptor, the effects of EP2 and FP receptor stimulation on aqueous humor outflow are similar.