The effect of topical PGF2 alpha on uveoscleral outflow and outflow facility in the rabbit eye

Effects of 0.4% ripasudil hydrochloride hydrate on morphological changes in rabbit eyes

We evaluated the cellular structure changes after continuous use of ripasudil hydrochloride hydrate in rabbit eyes which might affect its own efficacy and adverse effects. Two pigmented Dutch rabbits and 1 Japanese white rabbit were instilled with 0.4% ripasudil hydrochloride hydrate to the left eye twice daily. The right eye was observed as the control. Both eyes of all 3 rabbits were then enucleated for histopathologic examination by light and electron microscope at 1mo in 1 of the pigmented Dutch rabbits, 3mo in the other pigmented Dutch rabbit, and in the Japanese white rabbit after instillation. Microscopic observations showed increase intercellular space in trabecular meshwork, ciliary body, and iris stoma, increase pigmented granule number and size in iris epithelial cells, and decrease actin filament in iris muscle fiber cells. Consequently, ripasudil hydrochloride hydrate decreases the intraocular pressure by improving the conventional outflow and may also facilitate the unconventional outflow via intercellular space widening without serious side effects.

Effect of topical ophthalmic administration of 0.005% latanoprost solution on aqueous humor flow rate and intraocular pressure in ophthalmologically normal adult Beagles

OBJECTIVE

To determine the effect of topical ophthalmic administration of 0.005% latanoprost solution on aqueous humor flow rate (AHFR) and intraocular pressure (IOP) in ophthalmologically normal dogs.

ANIMALS

12 adult Beagles.

PROCEDURES

In a masked crossover design involving two 10-day experimental periods separated by a 7-day washout period, dogs were randomly assigned to first receive latanoprost or artificial tears (control) solution and then the opposite treatment in the later experimental period. Each experimental period was divided into a baseline phase (days 1 to 3), baseline fluorophotometry assessment (day 4), treatment phase (1 drop of latanoprost or artificial tears solution administered twice daily in each eye on days 5 to 9 and once on day 10), and posttreatment fluorophotometry assessment (day 10). Measured fluorescein concentrations were used to calculate baseline and posttreatment AHFRs. The IOP was measured 5 times/d in each eye during baseline and treatment (days 5 to 9) phases.

RESULTS

Mean baseline and posttreatment AHFR values did not differ significantly in either experimental period (latanoprost or control). In the latanoprost period, mean IOP was significantly lower during treatment than at baseline; there was no difference in corresponding IOP values during the control period. In the latanoprost period, mean IOP was significantly higher on the first day of treatment than on subsequent treatment days.

CONCLUSIONS AND CLINICAL RELEVANCE

In ophthalmologically normal dogs, topical ophthalmic administration of 0.005% latanoprost solution significantly decreased IOP but did not affect AHFR. Thus, the ocular hypotensive effect of latanoprost did not appear to have been caused by a reduction in aqueous humor production. (Am J Vet Res 2019;80:498-504).

A Novel Uveolymphatic Drainage Pathway-Possible New Target for Glaucoma Treatment

Glaucoma is a heterogeneous group of ophthalmic diseases leading to irreversible damage to the optic nerve. While the overall mechanism responsible for glaucoma remains obscure, the most important risk factor is elevated intraocular pressure. The current therapies, whether pharmacological or surgical, are primarily symptomatic with the aim to lower the intraocular pressure (IOP). Poorer response to treatment is associated, for example, with pseudoexfoliation glaucoma, which is determined by blocking the trabecular meshwork (TM) both by pigment grains and the pseudoexfoliation material. It was thought that aqueous humor is drained from the eye by two main pathways: conventional outflow through the TM and Schlemm's canal; and unconventional outflow through the ciliary body through uveal tissue. In 2009 Yucel et al. described and proved the presence of a third pathway for aqueous humor drainage using two specific lymphatic markers: podoplanin, and lymphatic vessel endothelial hyaluronan receptor-1 to identify lymphatic channels in the human ciliary body. The discovery identifies a novel target for IOP-lowering therapies. The most promising group are prostaglandins, which are widely prescribed for glaucoma patients. An intriguing new possibility in glaucoma therapy is using ANGPT agonist. It is still not known if the lymphatic drainage in glaucoma is decreased or dysfunctional and whether lymphatic stimulation can help in removing the improperly accumulated substances, as is seen in pseudoexfoliation glaucoma. However, this new target for glaucoma treatment appears very promising.

Unconventional aqueous humor outflow: A review

Aqueous humor flows out of the eye primarily through the conventional outflow pathway that includes the trabecular meshwork and Schlemm's canal. However, a fraction of aqueous humor passes through an alternative or 'unconventional' route that includes the ciliary muscle, supraciliary and suprachoroidal spaces. From there, unconventional outflow may drain through two pathways: a uveoscleral pathway where aqueous drains across the sclera to be resorbed by orbital vessels, and a uveovortex pathway where aqueous humor enters the choroid to drain through the vortex veins. We review the anatomy, physiology and pharmacology of these pathways. We also discuss methods to determine unconventional outflow rate, including direct techniques that use radioactive or fluorescent tracers recovered from tissues in the unconventional pathway and indirect methods that estimate unconventional outflow based on total outflow over a range of pressures. Indirect methods are subject to a number of assumptions and generally give poor agreement with tracer measurements. We review the variety of animal models that have been used to study conventional and unconventional outflow. The mouse appears to be a promising model because it captures several aspects of conventional and unconventional outflow dynamics common to humans, although questions remain regarding the magnitude of unconventional outflow in mice. Finally, we review future directions. There is a clear need to develop improved methods for measuring unconventional outflow in both animals and humans.

Non-continuous measurement of intraocular pressure in laboratory animals

Glaucoma is a leading cause of blindness, which is treatable but currently incurable. Numerous animal models therefore have both been and continue to be utilized in the study of numerous aspects of this condition. One important facet associated with the use of such models is the ability to accurately and reproducibly measure (by cannulation) or estimate (by tonometry) intraocular pressure (IOP). At this juncture there are several different approaches to IOP measurement in different experimental animal species, and the list continues to grow. We feel therefore that a review of this subject matter is timely and should prove useful to others who wish to perform similar measurements. The general principles underlying various types of tonometric and non-tonometric techniques for non-continuous determination of IOP are considered. There follows discussion of specific details as to how these techniques are applied to experimental animal species involved in the research of this disease. Specific comments regarding anesthesia, circadian rhythm, and animal handling are also included, especially in the case of rodents. Brief consideration is also given to possible future developments.

Pharmacology of topical prostaglandin F2 α analogs and their place in the treatment of glaucoma in small animals

A distinguishing feature of the most common types of glaucoma is an increased intra-ocular pressure (IOP), which has a damaging effect on optic nerve axons, leading to the progressive loss of retinal ganglion cells. Therefore, IOP-lowering medications are the mainstay of glaucoma therapy. Topical prostaglandin F2 α analogs (PGAs) are a relatively new class of ocular hypotensive drugs, which have made a huge impact on the treatment of glaucoma in dogs. This study summarizes the current state of knowledge on the mechanism of action of these agents and their effect on IOP in dogs and cats. It also discusses potential harmful side effects of PGAs and presents contemporary opinions about their role and place in the medical management of glaucoma in small animals.

Sildenafil accelerates anterior chamber refilling after paracentesis in sheep and rabbits

PURPOSE

Sildenafil increases ocular blood flow. Thus, the authors investigated if it also increases anterior chamber (AC) refilling after paracentesis.

METHODS

Corriedale sheep and albino rabbits were used as animal models. Intraocular pressure (IOP) was measured, paracentesis performed on one eye, and AC refilling followed by observation using oblique illumination. IOP measurements continued as the AC formed. After IOP stabilization, sildenafil (100 mg) was orally administered. Forty to 60 minutes later, AH was withdrawn from the contralateral eye. The point at which IOP recovered was used to determine refilling time. Paracentesis volumes were either 60, 120, or 300 μL in sheep, and 50 or 100 μL in rabbits.

RESULTS

IOP recovered in approximately 49, 56, and 50 minutes after the 60, 120, and 300 μL withdrawals in sheep. The refilling times of the contralateral eye after sildenafil ingestion were approximately 19, 26, and 37 minutes for the respective AH withdrawals. With rabbits, IOP recovered in approximately 13 minutes after the 50 and 100 μL AH withdrawals. After sildenafil, the IOP recovery times of the fellow eye were approximately 6 minutes. AH refilling rates were estimated by dividing the paracentesis volume by IOP recovery time. After sildenafil, such rates were larger than the AH formation rate attributed to secretion by the ciliary epithelium.

CONCLUSIONS

Sildenafil accelerates the rate of AC refilling and might have beneficial utility as an agent enhancing fluid entry into the AC of patients who experienced AH loss during eye surgery, as well as in some cases of ocular hypotony.

Episcleral venous pressure responses to topical nitroprusside and N-Nitro-L-arginine methyl ester

PURPOSE

To determine the episcleral venous pressure (EVP) responses to nitroprusside (NP) and L-NAME.

METHODS

In anesthetized rabbits (n = 36), arterial pressure and IOP were measured by direct cannulation, and carotid blood flow and heart rate were measured with an ultrasound flowmeter and cardiotachometer. EVP was measured in two groups with a servonull system. Group 1 (n = 13) was given NP (50 microL, 10 mg/mL). Group 2 (n = 10) was given L-NAME (100 microL, 10 mg/mL) followed by NP (50 microL, 10 mg/mL). In group 3 (n = 13), fluorophotometric aqueous flow was measured before and after NP (100 microL, 10 mg/mL).

RESULTS

Systemic parameters were unaffected by treatment in all groups. In group 1, NP increased EVP from 9.1 +/- 0.6 to 11.6 +/- 0.8 mm Hg (P < 0.01) and IOP from 18.7 +/- 1.4 to 23.9 +/- 1.6 mm Hg (P < 0.01). In group 2, L-NAME lowered EVP from 11.5 +/- 1.2 to 8.8 +/- 1.0 mm Hg (P < 0.01) and subsequent NP increased EVP to 13.9 +/- 1.7 mm Hg (P < 0.01 versus L-NAME and baseline). L-NAME decreased IOP from 20.8 +/- 1.7 to 16.7 +/- 1.8 mm Hg (P < 0.01), and then it increased to 20.7 +/- 1.3 mm Hg after NP (P < 0.01 versus L-NAME and P > 0.05 versus baseline). In group 3, NP increased IOP from 16.6 +/- 0.7 to 20.0 +/- 0.9 mm Hg (P < 0.01) but did not alter aqueous flow (2.65 +/- 0.3 vs. 3.0 +/- 0.3 microL/min, P > 0.05).

CONCLUSIONS

Because a topical NO donor raises EVP and a topical NO synthase inhibitor lowers EVP, the authors conclude that EVP is modulated by NO.

Histologic effect of semiconductor diode laser transscleral cyclophotocoagulation on the normal equine eye

OBJECTIVE

To determine the acute histologic effects of semiconductor diode laser transscleral cyclophotocoagulation (TSCP) on the normal equine eye.

ANIMAL STUDIED

Part 1: eight eyes of four horses. Part 2: 10 eyes of five horses.

MATERIALS AND METHODS

Part 1: TSCP was performed on four eyes at 4 mm and four eyes at 6 mm posterior to the limbus with 15 sites treated in four quadrants at 1800 mW for 1500 ms. The globes were sectioned transversely or sagitally to examine all quadrants and histologic sections were taken every 1 mm for the entire globe. Part 2: Based on the results from Part 1, TSCP was performed at 20 sites 4 mm posterior to the dorsotemporal limbus with a constant energy varying from 0.75 to 4 J/site. Histologic sections were taken every 1 mm for a total of 10 sections per eye and 20 sections per energy level group.

RESULTS

Part 1: At 4 mm posterior to the limbus, coagulation of the nonpigmented epithelium (NPE) of the pars plicata was observed in the temporal (14%) and dorsal quadrants (12%). Retinal detachment was observed in the nasal quadrant (12%). Hemorrhage was common in the nasal (19%) and temporal (12%) quadrants. At 6 mm posterior to the limbus, coagulation of the NPE of the pars plicata was observed in the dorsal (14%), ventral (16%), nasal (2%), and temporal (2%) quadrants. Retinal detachment was observed in the dorsal (8%), ventral (18%), nasal (20%) and temporal (2%) quadrants. Part 2: Settings of 0.75 J/site were ineffective; 1.5, 2.25 and 3 J/site damaged the pars plicata without disruption of anatomy; and 4 J/site caused disruption of normal architecture.

CONCLUSIONS

The most appropriate site for equine TSCP appears to be 4 mm posterior to the dorso- and ventrotemporal limbus avoiding the 3 and 9 o'clock positions and using an initial energy setting of 2.25 J/site. This results in effective damage to the pars plicata while minimizing surgical complications such as retinal detachment and hemorrhage.

Contribution of ROCK in contraction of trabecular meshwork: proposed mechanism for regulating aqueous outflow in monkey and human eyes

Aqueous outflow in the conventional outflow pathway is regulated by the contraction and relaxation of the ciliary muscle (CM) and the trabecular meshwork (TM). Rho-associated coiled coil-forming protein kinase (ROCK) is thought to regulate actomyosin-based contractility in many types of cells by phosphorylation of ROCK substrates. In animal models, ROCK inhibitor Y-39983 relaxed CM and TM and decreased intraocular pressure (IOP). Thus, ROCK is implicated in the regulation of aqueous outflow and IOP. However, the site of action of ROCK in monkey and man is unknown. In the present communication, RT-PCR analysis of monkey tissues showed higher levels of mRNAs for ROCK and ROCK substrates in TM compared to CM. Human TM also showed higher levels of mRNAs for ROCK and ROCK substrates compared to CM. Differences between TM and CM in human were not as high as in monkey. ROCK inhibitor Y-39983 led to a dose-dependent relaxation of carbachol-induced, contracted TM from monkey. In contrast, Y-39983 was only slightly effective in relaxing CM. Our results suggested that TM was one of the major sites for regulating IOP by ROCK. ROCK inhibitor Y-39983 might be a candidate drug for lowering IOP by increasing conventional outflow and producing fewer side effects on accommodation and miosis.

Effects of the Rho kinase inhibitor Y-27632 and the phosphatase inhibitor calyculin A on outflow facility in monkeys

Previous studies have shown that the inhibition of Rho kinase is involved in the regulation of outflow facility in the live rabbit eye and the enucleated porcine eye. However, it is unknown whether the Rho kinase inhibition will do the same in non-human primates. To determine if the Rho kinase inhibitor Y-27632 will reduce outflow resistance in the live monkey eye, if Y-27632 and the phosphatase inhibitor calyculin A (Caly-A which antagonises Y-27632-induced MLC dephosphorylation) will affect outflow facility differently, and if the latter will inhibit effect of the former on facility, we studied effects of Y-27632 and Caly-A on outflow facility in living monkeys separately and concurrently. Total outflow facility was measured by 2-level constant pressure perfusion of the anterior chamber (AC) before and after exchange with different doses of Y-27632 (1, 10 and 100 microM) or Caly-A (10, 50 and 100 nM), or vehicles, followed by continuous AC infusion of corresponding drug/vehicle solution, in opposite eyes of cynomolgus or rhesus monkeys. The effect of 100 microM Y-27632 or 100 nM Caly-A vs vehicle and the effect of 100 microM Y-27632+100 nM Caly-A vs 100 microM Y-27632 alone on outflow facility were also determined in monkeys pre-treated topically with 10 microl of 1% atropine in both eyes 1 hr before perfusion. Both Y-27632 and Caly-A dose-dependently increased outflow facility by up to 2-3 fold in monkeys, adjusted for baseline and contralateral control eye washout. Pre-treatment with 1% topical atropine partially inhibited the effect of 100 nM Caly-A, but not 100 microM Y-27632, on outflow facility. 100 nM Caly-A gradually and partially inhibited the Y-27632-induced facility increase. In conclusion, Y-27632 increases outflow facility in monkeys presumably by inhibiting cellular contractility in the TM. Caly-A increases outflow facility by complicated mechanisms perhaps including drug-induced ciliary muscle contraction and cytoskeletal reorganisation in TM cells. The partial inhibitory effect of Caly-A on the Y-27632-induced increase in outflow facility may reflect the former partially inhibiting the latter's relaxation of cells in the TM.

Characterization of uveoscleral outflow in enucleated porcine eyes perfused under constant pressure

PURPOSE

A new technique was developed to measure the flow of aqueous humor through the uveoscleral pathway in porcine eyes and to examine whether there is any outflow through the choroid into the vortex veins.

METHODS

Enucleated porcine eyes were perfused in vitro under a constant pressure of 10 mm Hg. After total outflow was measured, the episcleral vessels were blocked with cyanoacrylate to eliminate outflow through the conventional pathway. The vortex veins were then blocked, to assess the amount of choroidal drainage.

RESULTS

The average outflow in control eyes was found to be 2.8 +/- 0.9 microL/min. After the exit sites of the conventional pathway were blocked, the average outflow decreased to 1.1 +/- 0.5 microL/min. Blocking the vortex veins did not appear to alter uveoscleral outflow further (1.2 +/- 0.8 microL/min).

CONCLUSIONS

The results suggest that choroidal drainage into the vortex veins is insignificant in the absence of blood perfusion. No significant washout effects in porcine eyes were observed.

Effect of Different Dose Schedules of 0.15% Unoprostone Isopropyl on Intraocular Pressure and Pupil Size in the Glaucomatous Beagle

The changes in intraocular pressure (IOP) and pupil size (PS) after instillations of 0.15% unoprostone isopropyl (Rescula, Novartis Ophthalmics, Duluth, GA) were investigated in the spontaneous glaucoma Beagle model. From the first-day baseline IOP of 27.3+/-3.2 mmHg placebo eye and 32.8+/-5.1 mmHg control eye, the mean+/-standard error of the mean (SEM) diurnal changes after 0.15% unoprostone, at 8 AM once-daily for the next 4 days, were 15.5+/-1.3 mmHg, 14.7+/-1.9 mmHg, 16.1+/-1.1 mmHg, and 17.0+/-1.5 mmHg, respectively, and were significantly different from the control eye. After 0.15% unoprostone was instilled at 8 PM, the mean+/-SEM baseline changes from the baseline IOP (insert drug eye 9 AM) in the drug eyes were 5.9+/-2.5 mmHg, 5.2+/-4.1 mmHg, 9.7+/-2.5 mmHg, and 3.6+/-3.6 mmHg, respectively. When 0.15% unoprostone was instilled twice-daily, the mean+/-SEM baseline IOP (insert drug eye 9 AM) changes were 13.6+/-0.7 mmHg, 13.9+/-1.4 mmHg, 11.3+/-1.0 mmHg, and 9.3+/-1.4 mmHg, respectively, and were significantly different from the control eyes. Miosis occurred within 2 hours and lasted several hours. Unoprostone isopropyl instilled once-daily (AM or PM), as well as twice-daily, produces significant decreases in IOP and PS in the glaucomatous Beagle.

Effect of different dose schedules of travoprost on intraocular pressure and pupil size in the glaucomatous Beagle

OBJECTIVE

To evaluate changes in intraocular pressure and pupil size in glaucomatous dogs after instillation of 0.004% travoprost once in the morning, or once in the evening, or twice daily in 5-day multiple dose studies.

MATERIALS AND METHODS

Applanation tonometry (IOP) and pupil size (PS) measurements were obtained at 8 a.m., 10 a.m., 12 noon, 2 p.m. and 4 p.m. in eight glaucoma dogs. Methylcellulose (0.5% as placebo) was instilled in the control eye, and 0.004% travoprost was instilled in the opposite drug eye. Methylcellulose (0.5%) and 0.004% travoprost were instilled on the 2nd through to the 5th day with instillations in the morning (8.30 a.m.), or evening (8 p.m.), or twice daily (8.30 a.m. and 8 p.m.).

RESULTS

The mean +/- SEM diurnal changes from baseline IOP in the control and placebo eyes in all three studies ranged from 1.2 +/- 0.3 mmHg to 3.2 +/- 0.9 mmHg. The mean +/- SEM diurnal changes from the baseline IOP after 0.004% travoprost at 8 a.m. once daily for the next 4 days were 19.0 +/- 2.7 mmHg, 24.7 +/- 2.7 mmHg, 24.9 +/- 3.1 mmHg, and 24.7 +/- 3.1 mmHg, respectively, and were significantly different from the control eye. After travoprost was instilled at 8 p.m., the mean +/- SEM baseline changes from the baseline IOP in the drug eyes were 23.5 +/- 2.2 mmHg, 24.2 +/- 2.2 mmHg, 24.5 +/- 2.3 mmHg, and 24.2 +/- 2.3 mmHg, respectively. When 0.004% travoprost was instilled twice daily, the mean +/- SEM baseline IOP changes were 27.7 +/- 2.1 mmHg, 28.1 +/- 2.1 mmHg, 28.4 +/- 2.2 mmHg, and 28.5 +/- 2.2 mmHg, respectively, and were significantly different from the control eyes. Miosis of varying duration was frequent during the three studies.

CONCLUSION

Travoprost instilled once daily (a.m. or p.m.) as well as twice daily produces significant decreases in IOP and PS in the glaucomatous Beagle.

Hydrolysis of bimatoprost (Lumigan) to its free acid by ocular tissue in vitro

We determined whether bimatoprost, which has been reported to act via putative prostamide receptors, could be hydrolyzed to its free acid (17-phenyl-PGF(2 alpha)), a potent FP receptor agonist, by human ocular tissue in vitro. We developed a gas chromatography/mass spectrometric method to measure 17-phenyl-PGF(2 alpha) levels at sub-picomolar levels. We then analyzed the amount of 17-phenyl-PGF(2 alpha) present after incubation of 50 microl Lumigan (0.03% bimatoprost) with eye tissue using this assay. We found that cornea, sclera, iris, and ciliary body, all rapidly hydrolyzed bimatoprost to 17-phenyl-PGF(2 alpha) with linear kinetics at a rate of 6.3, 2.0, 2.8, and 1.5 pmol mg tissue(-1) hr(-1), respectively. For cornea, sclera, and ciliary body, this linear rate of hydrolysis continued over a period of at least three hours, while iris-induced hydrolysis did not continue beyond one hour. Our findings suggest that bimatoprost can act as prodrug for FP receptor activation and questions the concept of a "prostamide receptor" agonist.

Effect of different dose schedules of bimatoprost on intraocular pressure and pupil size in the glaucomatous Beagle

The changes in intraocular pressure and pupil size in glaucomatous dogs were evaluated after instillations of 0.03% bimatoprost (Lumigan, Allergan, Irvine, CA USA) once in the morning, or once in the evening, or twice daily in five day multiple dose studies. Applanation tonometry (IOP) and pupil size (PS) measurements were obtained at 8 am, 10 am, 12 noon, 2 pm, and 4 pm in 8 glaucoma dogs. Methylcellulose (0.5% as placebo) was instilled in the control eye, and 0.03% bimatoprost was instilled in the opposite drug eye. Methylcellulose (0.5%) and 0.03% bimatoprost were instilled the second through the fifth days with instillations in the morning (8:30 am), or evening (8 pm), or twice daily (8:30 am and 8 pm). The mean +/- SEM diurnal changes in IOP from baseline values after 0.03% bimatoprost at 8 am once daily for the next four days were 25.0 +/- 3.2 mm Hg, 25.6 +/- 2.9 mm Hg, 25.5 +/- 3.0 mm Hg, and 26.0 +/- 3.2 mm Hg respectively, and were significantly different from the control eye. After bimatoprost was instilled at 8 pm, the mean +/- SEM changes in IOP from baseline values in the drug eyes were 27.3 +/- 2.4 mm Hg, 26.6 +/- 2.2 mm Hg, 27.2 +/- 2.5 mm Hg, and 27.3 +/- 2.6 mm Hg respectively. When 0.03% bimatoprost was instilled twice daily, the mean +/- SEM changes in IOP from baseline values were 39.1 +/- 2.3 mm Hg, 39.9 +/- 2.2 mm Hg, 39.9 +/- 2.3 mm Hg, and 39.6 +/- 2.1 mm Hg respectively, and were significantly different from the control eyes. Miosis of varying duration was frequent during the three studies. Bimatoprost instilled once daily (am or pm) as well as twice daily produces significant decreases in IOP and PS in the glaucomatous Beagle.

A myosin light chain kinase inhibitor, ML-9, lowers the intraocular pressure in rabbit eyes

The role of myosin light chain kinase (MLCK) in regulating the intraocular pressure (IOP) and outflow facility in rabbit eyes were studied. The IOP and pupil diameter were determined before and after intracameral and intravitreal administration of ML-9, a specific MLCK inhibitor. Total outflow facility and uveoscleral outflow facility was determined 3hr after intracameral administration of ML-9. Immunoblotting was performed to identify MLCK and the 20-kDa light chain of myosin (MLC) isoforms in human trabecular meshwork (TM) cells. The phosphorylation status of MLC was examined following ML-9 treatment. The effects of ML-9 on the morphology and actin and vinculin distribution in cultured TM cells were also studied. In rabbit eyes, administration of ML-9 resulted in a dose-dependent decrease in IOP. An increase of the outflow facility was also observed. Immunoblot analysis revealed the presence of MLCK in human TM cells. Exposure to ML-9 dose-dependently inhibited MLC phosphorylation/activation. The inhibitor caused retraction and dissociation of cells, disruption of actin bundles and impairment of focal adhesion formation in TM cells. ML-9 induces a reduction in IOP and an increase in the outflow facility in rabbit eyes. The IOP-lowering effects may be related to alterations in TM cell shapes. Inhibitors of MLCK may potentially be developed into novel medications for glaucoma.

Effect of different dose schedules of latanoprost on intraocular pressure and pupil size in the glaucomatous Beagle

OBJECTIVE

To evaluate the changes in intraocular pressure and pupil size in glaucomatous dogs after instillation of 0.005% latanoprost (Xalatan, Pharmacia and Upjohn, Kalamazoo, MI, USA) once in the morning, or once in the evening, or twice daily in five-day multiple-dose studies. Animals studied Eight Beagles with the moderate stage of inherited primary open-angle glaucoma.

PROCEDURES

Applanation tonometry (IOP) and pupil size (PS) measurements were obtained at 8 am, 10 am, 12 noon, 2 pm, and 4 pm in eight glaucoma dogs. Methylcellulose (0.5% as placebo) was instilled in the control eye, and 0.005% latanoprost was instilled in the opposite drug eye. Control and drug eyes were selected using a random table. For these three studies, 0.5% methylcellulose and 0.005% latanoprost were instilled the second through the fifth days with instillations in the morning (8.30 am), or evening (8 pm), or twice daily (8.30 am and 8 pm). Statistical comparisons between drug groups included control, placebo, and treated (0.005% latanoprost) eyes for three multiple-dose studies.

RESULTS

In the 8-am latanoprost study, the mean +/- SEM diurnal declines in IOP for the placebo and drug eyes for the first day were 6.5 +/- 3.6 mmHg and 8.4 +/- 4.0 mmHg, respectively. The mean +/- SEM diurnal changes in IOP after 0.005% latanoprost at 8 am once daily for the next four days were 23.3 +/- 5.0 mmHg, 25.4 +/- 2.1 mmHg, 25.7 +/- 1.7 mmHg, and 26.1 +/- 1.7 mmHg, respectively, and were significantly different from the control eye. A significant miosis also occurred starting 2 h postdrug instillation, and the resultant mean +/- SD pupil size was 1.0 +/- 0.1 mm. In the first day of the second latanoprost study, the mean +/- SEM diurnal changes in the placebo and drug eye IOPs were 11.6 +/- 3.8 mmHg, and 12.0 +/- 4.4 mmHg, respectively. For the following four days with latanoprost instilled at 8 pm, the mean +/- SEM diurnal changes in IOP in the drug eyes were 24.9 +/- 2.1 mmHg, 22.4 +/- 1.8 mmHg, 21.6 +/- 1.9 mmHg, and 26.6 +/- 2.2 mmHg, respectively. Compared to the fellow placebo eyes, the diurnal changes in IOP were significantly different. Significant changes in pupil size were similar to the IOP changes, with miosis throughout the day and return to baseline pupil size the following morning before drug instillation. In the last study, the mean +/- SEM diurnal changes in IOP for the placebo and drug eyes for the first day were 6.6 +/- 2.1 mmHg and 9.4 +/- 2.8 mmHg, respectively. For the four subsequent days with latanoprost instilled twice daily, the mean +/- SEM diurnal IOP changes were 19.6 +/- 1.5 mmHg, 19.1 +/- 1.4 mmHg, 19.9 +/- 1.7 mmHg, and 20.3 +/- 0.7 mmHg, respectively, and were significantly different from the placebo eyes. The mean changes in PS were 3.1 +/- 0.7 mm.

CONCLUSION

0.005% latanoprost instilled once daily (am or pm) as well as twice daily produces significant decreases in IOP and PS in the glaucomatous Beagle. The evening instillation of 0.005% latanoprost produced less daily fluctuations in IOP than when the drug was instilled in the morning. 0.005% latanoprost instilled twice daily produced the greatest decline in IOP with the least daily fluctuations, but longer duration miosis.

Involvement of phosphorylation of myosin phosphatase by ROCK in trabecular meshwork and ciliary muscle contraction

The control of smooth muscle contraction is an important factor in maintaining normal intraocular pressure. However, the specific factors causing changes in control by phosphorylation/dephosphorylation schemes in the eye are not well-defined. The purposes of this experiment were to (i) determine the localization of ROCK (Rho-associated, coiled coil-forming kinase) in monkey and rabbit eye tissues and (ii) measure phosphorylation of ROCK substrate during trabecular meshwork or ciliary muscle contraction induced by carbachol. We found that mRNAs for both ROCK I and II were expressed in most eye tissues from rabbit and monkey. Proteins for ROCK I and II were present in all eye tissues studied except lens. When trabecular meshwork or ciliary muscle were incubated with carbachol to induce contraction, phosphorylation of the myosin-binding subunit (MBS) of myosin phosphatase, a substrate for ROCK, started within 1 min and continued for at least 1 h. This phosphorylation was well correlated with contraction of trabecular meshwork or ciliary muscle. These results suggested that ROCK might regulate contraction of trabecular meshwork or ciliary muscle through phosphorylation of MBS of myosin phosphatase.

Constitutive expression and localization of COX-1 and COX-2 in rabbit iris and ciliary body

Prostaglandins are involved in the regulation of intraocular pressure and the blood-aqueous barrier of the eye, and are used for the treatment of glaucoma. The decrease of the constitutively expressed PG-synthesizing enzyme cyclooxygenase-2 (COX-2) has been demonstrated in the ciliary non-pigmented epithelial layer of patients with primary open angle glaucoma. Little is known about the distribution of COX-1 and COX-2 in animals. We investigated this in the iris and ciliary body of the normal rabbit eye. The presence of COX-1 and COX-2 in freshly excised iris and ciliary body tissue from adult New Zealand White albino rabbits was demonstrated by real-time RT-PCR, and Western blot analysis. The localization of both isoforms and of the neuron-specific protein gene product 9.5 was determined by indirect immunofluorescence. Both enzymes are expressed in the iris and the ciliary body. Immunofluorescence studies including double staining techniques localized COX-1 and COX-2 to about 50% of cells in the stromal tissue of iris and ciliary body, mainly on the corneal side. They were co-localized in about 75% of these cells. Whereas all stained cells were positive for COX-1, COX-2 showed a gradient-like distribution in the stroma, with some restriction of expression near the epithelial layers, which we clearly showed to be completely negative for both COX-1 and COX-2. Also, neuronal elements did not show COX-1 or COX-2 immunoreactivity. These results establish the presence of COX-1 and COX-2 on the RNA and protein levels in normal, unstimulated rabbit iris and ciliary body. The pattern of distribution suggests a role for both enzymes in maintaining the physiology of the eye. In contrast to our results in man, non-pigmented epithelial cells of the ciliary body did not express immunoreactivity. This could account for differences in the regulation of intraocular pressure and/or blood-aqueous barrier between human and rabbit eyes.

Advances in glaucoma diagnosis and therapy for the next millennium: new drugs for trabecular and uveoscleral outflow

Advances in our understanding of the physiology and molecular biology of the trabecular and uveoscleral outflow pathways of the eye will lead to the development of new approaches for glaucoma therapy. Therapies of the future will target the structures and enzymes involved in maintaining cell shape and cell-cell and cell-extracellular matrix interactions. Altering the extracellular matrix in the ciliary muscle has been important in the intraocular pressure lowering effects of prostaglandins and will be developed further as an approach to enhancing outflow through the trabecular meshwork. Gene therapy may be used to enhance or suppress the endogenous targets that are ultimately responsible for the outflow enhancement triggered by these agents.

Acute versus chronic effects of brimonidine on aqueous humor dynamics in ocular hypertensive patients

PURPOSE

To report the acute vs chronic effects of brimonidine, a selective alpha2-adrenergic receptor agonist, on aqueous humor dynamics in ocular hypertensive patients.

METHODS

Brimonidine 0.2% was given topically twice daily for 29 days to one eye each of 28 ocular hypertensive volunteers in a randomized double-masked study. The fellow eye was similarly treated with vehicle. Aqueous flow (Fa) and outflow facility (Cfl) were determined with fluorophotometry. Intraocular pressure, outflow facility (Cton), and episcleral venous pressure (Pev) were measured with pneumatonometry, tonography, and venomanometry, respectively. Uveoscleral outflow (Fu) was calculated from intraocular pressure, Fa, Pev, and Cfl values. All measurements were taken on baseline day, day 8, and day 29 of treatment. Intraocular pressure and Fa only were measured after instillation of 1 drop of brimonidine on day 1.

RESULTS

When measured 3 hours after instillation on days 1, 8, and 29 of treatment, brimonidine significantly (P < .001) reduced intraocular pressure by at least 5.0 +/- 0.7 mm Hg (mean +/- SEM) compared with baseline day, and by 2.7 +/- 0.5 mm Hg compared with the vehicle-treated contralateral control eyes. The greatest decrease (6.0 +/- 0.6 mm Hg) was observed at 3 hours after the first drop. Aqueous flow was reduced by 29% (P < .001) after the first application but was not significantly different from baseline when measured at day 29 of treatment. Uveoscleral outflow was increased 60% at day 8 (P < .06) and day 29 (P < .05) compared with baseline. There was no significant difference in outflow facility or episcleral venous pressure at day 8 or day 29 of treatment.

CONCLUSIONS

The brimonidine-induced reduction in intraocular pressure in humans is associated initially with a decrease in aqueous flow, and after chronic treatment with an increase in uveoscleral outflow.

Trabecular outflow facility and formation rate of aqueous humor during anesthesia with sevoflurane-nitrous oxide or sevoflurane-remifentanil in rabbits

In the present study, we examined the effect of sevoflurane and remifentanil on intraocular pressure (IOP) and fluid dynamics. Twenty-eight rabbits were anesthetized with halothane, and IOP was measured via a 25-gauge needle in the anterior chamber. Rabbits were then assigned to one of four groups, and halothane was replaced with sevoflurane 1% (n = 7), 2% (n = 7), 3% (n = 7), or 1% + remifentanil 0.65 microg kg(-1) x min(-1) i.v. (n = 7). In all groups, a series of intraocular infusions was made into the anterior chamber, and IOP, trabecular outflow facility, the rate of aqueous humor formation, and intraocular compliance were determined. With sevoflurane only, intraocular compliance decreased (55 +/- 14, 39 +/- 22, 31 +/- 17 nL/mm Hg; P < 0.05) as the concentration of sevoflurane increased. With sevoflurane 1% + remifentanil, intraocular compliance was significantly increased (100.1 +/- 30.5 nL/mm Hg; P < 0.05) compared with sevoflurane 1%, 2%, or 3%. Trabecular outflow facility, rate of aqueous humor formation, and IOP did not differ among groups, and IOP was similar to values obtained during halothane anesthesia.

IMPLICATIONS

The dose-related effects of sevoflurane on intraocular compliance did not produce significant intraocular pressure differences. Adding remifentanil to sevoflurane increased intraocular compliance. Sevoflurane or sevoflurane + remifentanil causes a decrease in intraocular pressure compared with the average of previously reported values in awake rabbits, and the magnitude of the decrease is similar to that previously reported in rabbits anesthetized with ethyl urethane, pentobarbital, or halothane alone or in combination with propofol, cocaine, or lidocaine.

Prostaglandin derivates as ocular hypotensive agents

Low doses of naturally occurring prostaglandins reduce the intraocular pressure (IOP) in many species. Species differences do occur both in terms of efficiency and mechanism of action, and also among the different prostaglandins. Among the prostaglandins mainly PGF2 alpha has been tested in human eyes. Although it is an effective ocular hypotensive drug it is not clinically useful due to pronounced ocular side-effects, mainly conjunctival hyperemia and irritation, at doses that produce a maximal effect on IOP. Modification of the drug has resulted in two analogues that are now in clinical use, latanoprost and unoprostone. In long-term studies latanoprost, when applied as a once-daily dose of a 0.005% concentration, reduces IOP at least as effectively as adrenergic beta-receptor blockers. The reduction of IOP is due to increased outflow. This takes place mainly, or exclusively, through the uveoscleral routes, thus introducing a new pharmacological principle for the treatment of glaucoma. The drug reaches systemic concentrations that are below the level expected to stimulate FP-receptors outside the eye and it is rapidly eliminated with a half-life in plasma of 17 minutes, which explains why the clinical trials have not revealed any systemic side-effects with latanoprost. The most frequent side-effect observed with latanoprost is an increased pigmentation of the iris mainly in eyes with irides that are already partly brown. This effect is seen with several naturally occurring prostaglandins and is due to stimulation of melanin production in the melanocytes of the iridial stroma. No structural changes of the melanocytes have been observed in studies performed both in vivo and in vitro. The mechanism of action for unoprostone is the same as for latanoprost. No effect on iris colour has been reported for unoprostone but so far there is limited experience with the drug in eyes with a mixed iris colour.

The uveoscleral outflow routes

As there is no epithelial barrier between the anterior chamber and the ciliary muscle, aqueous humour may freely pass between the ciliary muscle bundles into the supraciliary and suprachoroidal spaces, from which it is drained through the sclera. This uveoscleral outflow of aqueous humour accounts for 40-60% of the total outflow in monkeys, whereas it is considerably less in (3-8%) in cats and rabbits. Direct measurements in human eyes have suggested that less than 15% is drained by the uveoscleral routes. However, indirect calculations have given a value of about 35% in young adults and 3% in elderly persons (> 60 years). Under normal conditions, in monkeys, the uveoscleral outflow is insensitive to changes in the intraocular pressure, but cyclodialysis and experimental uveitis increase the uveoscleral outflow and make it more pressure sensitive. The uveoscleral outflow is decreased by contraction (pilocarpine) and increased by relaxation (atropine) of the ciliary muscle. Thus, changing the tone of the ciliary muscle may redistribute aqueous humour between the conventional and uveoscleral outflow routes. Prostaglandins decrease the intraocular pressure by increasing the uveoscleral outflow. Two mechanisms seem to contribute to this effect: relaxation of the ciliary muscle and changes in extracellular matrix, causing decreased resistance in the uveoscleral outflow routes.

Effects of adenosine agonists on intraocular pressure and aqueous humor dynamics in cynomolgus monkeys

The effects of single or multiple topical doses of the relatively selective A1 adenosine receptor agonists (R)-phenylisopropyladenosine (R-PIA) and N6-cyclohexyladenosine (CHA) on intraocular pressure (IOP), aqueous humor flow (AHF) and outflow facility were investigated in ocular normotensive cynomolgus monkeys. IOP and AHF were determined, under ketamine anesthesia, by Goldmann applanation tonometry and fluorophotometry, respectively. Total outflow facility was determined by anterior chamber perfusion under pentobarbital anesthesia. A single unilateral topical application of R-PIA (20-250 micrograms) or CHA (20-500 micrograms) produced ocular hypertension (maximum rise = 4.9 or 3.5 mmHg) within 30 min, followed by ocular hypotension (maximum fall = 2.1 or 3.6 mmHg) from 2-6 hr. The relatively selective adenosine A2 antagonist 3,7-dimethyl-1-propargylxanthine (DMPX, 320 micrograms) inhibited the early hypertension, without influencing the hypotension. Neither 100 micrograms R-PIA nor 500 micrograms CHA clearly altered AHF. Total outflow facility was increased by 71% 3 hr after 100 micrograms R-PIA. In conclusion, the early ocular hypertension produced by topical adenosine agonists in cynomolgus monkeys is associated with the activation of adenosine A2 receptors, while the subsequent hypotension appears to be mediated by adenosine A1 receptors and results primarily from increased outflow facility.

Facility changes mediated by cAMP in the bovine anterior segment in vitro

The aim of this study was to investigate the influence of substances that increase intracellular cAMP levels on the aqueous humor outflow facility (C) of isolated bovine anterior segments. Anterior segments were perfused in vitro at a constant pressure of 10 mmHg for 270 min with a general protocol as follows: 90 min control perfusion with DMEM, 90 min of experimental perfusion with DMEM containing the test drug(s), and 90 min of postdrug-perfusion with DMEM. C was calculated as the ratio between the rate of medium inflow (microliter/min) and the perfusion pressure (mmHg). Anterior segments can be perfused in vitro for up to 5 hr without significantly modifying their C. The addition of epinephrine, forskolin, dibutyryl-cAMP or isobutylmethylxanthine to the control perfusion medium elicited a significant increase of C. If, during isobutylmethylxanthine perfusion, forskolin or epinephrine was added, C increased significantly. Finally, perfusion with indomethacin prior to addition of epinephrine prevented the increase of C induced by epinephrine. Epinephrine, the adenylate cyclase activator forskolin, the cAMP analog dibutyryl-cAMP, and the phosphodiesterase inhibitor isobutylmethylxanthine all increase aqueous facility. It seems reasonable to suspect that the cAMP system is involved in epinephrine's effects on bovine trabecular meshwork cells. Moreover, the complete inhibition by indomethacin of the outflow facility increase induced by epinephrine suggests that prostaglandins may be involved in the outflow facility mechanisms related to adrenoreceptor stimulation of trabecular meshwork cells.

Prostaglandin A2 increases uveoscleral outflow and trabecular outflow facility in the cat

Prostaglandins (PG) are very effective ocular hypotensive agents. It is generally agreed that these drugs reduce intraocular pressure primarily by increasing uveoscleral outflow. They may also increase trabecular outflow facility though available evidence is less convincing. It has been hypothesized that PGs may increase facility of uveoscleral outflow in addition to their other mechanisms, but this has not yet been tested. To help clarify the ocular hypotensive mechanism of action of a derived PG of the A type, cats were treated twice daily for one week with PGA2 (0.01%) to one eye and vehicle to the other. Measurements were made of aqueous flow and outflow facility with fluorophotometry and of intraocular pressure with pneumatonometry. From these values, uveoscleral outflow was calculated. In addition, total outflow facility, uveoscleral outflow, and uveoscleral outflow facility were determined with invasive methods. PGA2 significantly reduced IOP by a mean of at least 4.7 mmHg in all experiments with all P-values less than 0.01. Compared with contralateral vehicle-treated control eyes, uveoscleral outflow in the treated eye was significantly (P < 0.05) increased by at least 50% using two different methods of measurement. Compared with baseline day, PGA2 significantly (P < or = 0.05) increased aqueous flow by 1.8 microliters min-1, fluorophotometric outflow facility by 0.36 microliter min-1 mmHg-1 and fluorophotometric uveoscleral outflow by 2.0 microliters min-1. Total outflow facility was not significantly different comparing treated with contralateral control eyes. Facility of uveoscleral outflow was < or = 0.02 microliters min-1 mmHg-1 for both control and treated eyes. It is concluded that PGA2 decreases IOP in cats by increasing uveoscleral outflow and trabecular outflow facility as measured with fluorophotometry. A significant increase in aqueous flow reduces the ocular hypotensive effect.

Rate of anterior chamber aqueous formation, trabecular outflow facility, and intraocular compliance during desflurane or halothane anesthesia in dogs

The present study examined the effects of desflurane on intraocular pressure (IOP), the rate of anterior chamber aqueous formation, trabecular outflow facility, and intraocular compliance. The effects of desflurane were compared to those of halothane because the effects of halothane on intraocular fluid dynamics are well known. Twenty-two dogs were anesthetized for surgical preparation. Pancuronium was given intravenously to produce neuromuscular blockade, and the lungs were mechanically ventilated through a tracheal tube. After surgical preparation, anesthesia was maintained in Group 1 (n = 12) with halothane (0.8% expired) and in Group 2 (n = 10) with desflurane (7.0% expired). In both groups a series of intraocular infusions was made via a 30-gauge needle in the anterior chamber and IOP, aqueous formation, outflow facility, and intraocular compliance were determined. In Group 1 (halothane) IOP was 9.4 +/- 2.8 mm Hg (mean +/- SD), aqueous formation was 1.45 +/- 0.45 microL/min, outflow facility was 0.091 +/- 0.054 microL.min-1.mm Hg-1, and compliance was 377 +/- 282 nL/mm Hg. In Group 2 (desflurane) IOP was 11.3 +/- 3.8 mm Hg, aqueous formation was 1.61 +/- 0.56 microL/min, outflow facility was 0.097 +/- 0.062 microL.min-1.mm Hg-1, and compliance was 432 +/- 238 nL/mm Hg. These values did not differ between groups. It is concluded that in dogs aqueous humor dynamics during desflurane anesthesia are similar to those during halothane anesthesia.

Solubilization and characterization of PGE2 receptor in porcine ciliary epithelium

PGE2 binding sites or receptors of porcine ciliary nonpigmented epithelial (NPE) and pigmented epithelial (PE) membranes were solubilized with detergents (CHAPS and Triton X100). From the Scatchard plots of PGE2 binding to CHAPS-solubilized proteins, the Kd and Bmax values were calculated to be 35 nM and 470 fmol/mg protein for NPE protein and 65 nM and 430 fmol/mg protein for PE protein, respectively. On the basis of the Kd and Bmax values, the solubilized receptor proteins correspond to PGE2 binding sites of the membranes which have previously been shown to be coupled to adenylate cyclase inhibition. For both NPE and PE proteins, the order of binding potency was PGE2 > PGF2 alpha > PGD2. By gel filtration chromatography of NPE and PE proteins, the molecular mass of the major PGE2 binding peak was estimated to be about 150 KDa when solubilized in CHAPS and 46 KDa for Triton X100 extracts. The Bmax values of membrane-associated binding proteins were increased by GTP, indicating a close association of the PGE2 binding sites with a GTP-binding protein. However, GTP did not affect the Bmax values of detergent-solubilized receptor proteins.

Neuromodulatory effect of sulprostone on the circadian elevation of intraocular pressure in rabbits

Topical application of sulprostone, a preferential prostaglandin EP3 receptor agonist, caused a dose-dependent reduction of the circadian elevation of intraocular pressure (IOP) in New Zealand albino rabbits which were entrained to 12-hr/12-hr light-dark environment. Corresponding to the effect on IOP, 0.2 micrograms, 2 micrograms, and 20 micrograms sulprostone decreased the norepinephrine (NE) concentration in the aqueous humor in the dark phase. There was no breakdown of the blood-aqueous barrier. Bilateral applications of 2 micrograms and 20 micrograms sulprostone to entrained rabbits that had undergone unilateral, preganglionic transection of the cervical sympathetic trunk reduced the circadian IOP elevation in the intact eye, but caused little IOP change in the decentralized eye. These results indicate that the IOP-lowering effect of topical sulprostone in rabbits is dependent on sympathetic neural activity and that prejunctional inhibition of NE release may be an important mechanism of action.

Effects of PhXA41, a new prostaglandin F2 alpha analog, on aqueous humor dynamics in human eyes

PURPOSE

PhXA41, a new phenyl-substituted analog of a prostaglandin F2 alpha (PGF2 alpha) prodrug (13,14-dihydro-17-phenyl-18,19,20-trinor-prostaglandin F2 alpha-1-isopropyl ester), is an effective ocular hypotensive agent in patients with glaucoma. To understand its mechanism of action, various components of aqueous humor dynamics were examined after topical application to human eyes.

METHODS

In a randomized, double-masked, placebo-controlled study, PhXA41 (0.006%) was given topically twice daily for 1 week to one eye each of 22 volunteers with normotension or ocular hypertension. The other eye was similarly treated with vehicle. Intraocular pressure (IOP) was measured by pneumatonometry and tonographic outflow facility by pneumatonography. Aqueous flow and outflow facility were determined either directly or indirectly by a fluorophotometric technique, and uveoscleral outflow was calculated secondarily. Comparison of values obtained in treated versus contralateral control eyes and on baseline versus day 8 of treatment were made.

RESULTS

Compared with baseline measurements, PhXA41 significantly (P < 0.001) reduced IOP by 5.5 +/- 0.6 mmHg (mean +/- standard error of the mean) as measured 3 hours after the last dose on the eighth day of treatment. Aqueous flow, tonographic outflow facility, and fluorophotometric outflow facility were not changed by PhXA41. However, uveoscleral outflow was significantly greater in the PhXA41-treated eyes (0.87 +/- 0.22 microliter/minute) compared with either the contralateral vehicle-treated eyes (0.14 +/- 0.30; P < 0.02) or baseline measurements (0.39 +/- 0.20 microliter/minute; P < 0.05).

CONCLUSIONS

PhXA41 decreases IOP in humans by increasing uveoscleral outflow without significantly affecting other parameters of aqueous humor dynamics.

Intracamerally injected platelet activating factor (PAF) induces marked intraocular inflammatory reactions

An inflammatory response was elicited in the rabbit eye by intracameral injection of platelet activating factor (PAF). PAF induced severe aqueous flare, corneal edema, pupillary constriction and marked biphasic changes in intraocular pressure (IOP) in a dose-dependent manner. All of the responses to PAF were inhibited by the PAF receptor antagonist, BN 52021 (20 mg/kg, i.p.). The cyclooxygenase inhibitor, indomethacin (30 mg/kg, i.p.) caused significant inhibition of the early phase PAF-induced aqueous flare, pupillary constriction and intraocular hypertension, but did not effect PAF-induced corneal edema or intraocular hypotension. NDGA (10 mg/kg, i.p.), a lipoxygenase inhibitor, did not inhibit the inflammatory effects of PAF. PAF-induced chemotactic response was evaluated by tissue chemiluminescence. Intracamerally injected PAF did not significantly increase chemiluminescence in cornea or iris-ciliary body, but intracorneal injection of PAF did cause a chemotactic response in both the conjunctiva and cornea. These data suggest that PAF may be an important mediator of intraocular inflammation and that some PAF-induced effects are prostaglandin dependent, while others may be independent of eicosanoid synthesis and release.