Aqueous Humor Flow Research Articles

Effects of topical application of a 2% solution of dorzolamide on intraocular pressure and aqueous humor flow rate in clinically normal dogs.

To evaluate effects of topical application of a 2% solution of dorzolamide on intraocular pressure (IOP) and aqueous humor flow rate in clinically normal dogs. 15 Beagles. The IOP was measured in both eyes of all dogs for 3 days to determine baseline values. In a single-dose study, 50 microl of dorzolamide or control solution was applied in both eyes at 7:00 AM, and IOP was measured 7 times/d. In a multiple-dose study, dorzolamide or control solution was applied to both eyes 3 times/d for 6 days, and IOP was measured 4 times/d during treatment and for 5 days after cessation of treatment. Aqueous humor flow rate was measured for all dogs fluorophotometrically prior to treatment and during the multiple-dose study. In the single-dose study, dorzolamide significantly decreased IOP from 30 minutes to 6 hours after treatment. Mean decrease in IOP during this time span was 3.1 mm Hg (18.2%). Maximal decrease was detected 6 hours after treatment (3.8 mm Hg, 22.5%). In the multiple-dose study, dorzolamide decreased IOP at all time points, and maximal decrease was detected 3 hours after treatment (4.1 mm Hg, 24.3%). Mean aqueous humor flow rate decreased from 5.9 to 3.4 microl/min (43%) after treatment in the dorzolamide group. Topical application of a 2% solution of dorzolamide significantly decreases IOP and aqueous humor flow rate in clinically normal dogs. Therefore, topical administration of dorzolamide should be considered for the medical management of dogs with glaucoma.

Fluorophotometric determination of aqueous humor flow rate in clinically normal dogs.

To determine aqueous humor flow rate in clinically normal dogs, using fluorophotometry. 20 clinically normal Beagles. A study was performed on 5 dogs to establish an optimal protocol for fluorophotometric determination of aqueous humor flow rate. This protocol then was used to measure aqueous humor flow rate in 15 dogs. Corneas were loaded with fluorescein by topical application, and corneal and aqueous humor fluorescein concentrations were measured 5, 6.5, and 8 hours after application. Concentration-versus-time plots were generated, and slopes and ratios of the fluorescein concentration in the cornea and aqueous humor from these graphs were used to calculate flow rates. Calculations were performed by use of automated software provided with the fluorophotometer and by manual computation, and the 2 calculation methods were compared. The protocol established for the 5 dogs resulted in semilogarithmic and parallel decay of corneal and aqueous humor concentrations. Manually calculated mean +/- SD aqueous humor flow rates for left, right, and both eyes were 5.58 +/- 2.42, 4.86 +/- 2.49, and 5.22 +/- 1.87 microl/min, respectively, whereas corresponding flow rates calculated by use of the automated software were 4.54 +/- 3.08, 4.54 +/- 3.10, and 4.54 +/- 2.57 microl/min, respectively. Values for the left eye were significantly different between the 2 computation methods. Aqueous humor flow rates can be determined in dogs, using fluorophotometry. This technique can be used to assess pathologic states and medical and surgical treatments that alter aqueous humor dynamics.

Mechanism of Action of Bimatoprost (Lumigan™)

Bimatoprost is a new ocular hypotensive agent that lowers intraocular pressure (IOP) in normal, ocular hypertensive, and glaucomatous eyes. Its mechanism of action has been studied in normal human subjects. Bimatoprost mildly stimulates the rate of aqueous humor flow during the day (13%) and at night (14%). Its ocular hypotensive action is due primarily to a 26% reduction in the tonographic resistance to outflow. Thus, bimatoprost enhances the pressure-sensitive outflow pathway. Additional beneficial effects may include an increase in the rate of flow via the pressure-insensitive outflow pathway (sometimes called the “uveoscleral outflow pathway”) and a lowering of the extraocular recipient pressure (sometimes called “episcleral venous pressure”). Reduction of tonographic resistance to aqueous humor outflow reduces steady-state IOP, an effect that is beneficial for the treatment of glaucoma. In addition to its effect on steady-state IOP, reduction of resistance allows the eye to recover more quickly from transient IOP elevations. The former effect is common to all ocular hypotensive drugs, but the latter effect is an exclusive property of drugs that reduce outflow resistance, such as bimatoprost.

Naphazoline-induced Suppression of Aqueous Humor Pressure and Flow: Involvement of Central and Peripheral α2/I1Receptors

The objective of this study was to examine the ocular hydrodynamic effects of topically and centrally administered naphazoline, alone and following pretreatment with pertussis toxin (PTX) and α2/I1receptor antagonists. Topically and intracisternally administered naphazoline was examined for its ability to alter intraocular pressure (IOP) of rabbits in the absence and presence of receptor antagonists (rauwolscine, efaroxan) and a Gi/oribosylating agent PTX. In addition, the topical effects of naphazoline on pupil diameter and aqueous humor flow rate were evaluated. Topical unilateral application of naphazoline (7.5, 25 and 75μ g; 25μ l) elicited an ipsilateral dose-dependent mydriasis (2, 4 and 5.5mm) that peaked at 2hr with a duration of up to 5hr. The IOP decreases induced by naphazoline were bilateral and dose-dependent (3, 6 and 10mmHg); the response peaked at 1hr and lasted for up to 5hr. Pretreatment with efaroxan (250μ g) elicited significantly greater antagonism of the ocular hypotensive response to naphazoline than did rauwolscine (250μ g) suggesting an involvement of imidazoline (I1) receptors. Intracisternal application of naphazoline (3.3μ g) also produced bilateral reductions (6mmHg) of IOP that were immediate (10min post drug) and lasted for approximately 2hr. In PTX-pretreated (2.5μ gkg−1, i.a.) rabbits, the ocular hypotensive effects of naphazoline by both routes (topically and centrally) were attenuated by 50–65%. In addition to producing ocular hypotension, topical application of naphazoline (75μ g; 25μ l) caused significant reduction, from 2.8 to 1.5μ lmin−1, in aqueous humor flow. These in vivo data indicate that, regardless of route of administration, alteration of aqueous humor flow by naphazoline was induced by the activation of α2and I1receptors. The ocular hypotensive effects produced by central administration did not result in sedation, therefore, there is the suggestion that central α2adrenergic receptors were stimulated minimally by naphazoline. Thus, these data suggest that ocular hypotensive effects and suppression of aqueous humor flow rate by naphazoline are mediated, in part, by α2and/or central I1at both central (brain) and peripheral (eye) sites. Moreover, these data indicate that the receptors are linked to PTX-sensitive G(i/o)proteins.

Effects of AGN 192024, a new ocular hypotensive agent, on aqueous dynamics

PURPOSE: To determine the mechanism of intraocular pressure lowering for the Ocular Hypotensive Lipid, AGN 192024 (Allergan, Inc, Irvine, California). METHODS: Twenty-five normal human volunteers between the ages of 21 and 48 took part in a randomized, double-masked, placebo-controlled, paired-comparison study in which intraocular pressure, aqueous humor flow, and tonographic resistance to outflow were studied. Measurements of aqueous flow were made during the day and at night while subjects slept. Intraocular pressure was measured with the Goldmann tonometer, and resistance to outflow was measured by electronic recording Schiötz tonography. RESULTS: Intraocular pressure was decreased by 20% on day 3 in AGN 192024-treated eyes in comparison with placebo-treated eyes in normal subjects ( P < .001). Aqueous humor flow was stimulated 13% during the day ( P = .007) and 14% at night ( P = .014) by the drug. Tonographic resistance to outflow was decreased 26% by AGN 192024 ( P < .001), and apparent resistance to outflow (the ratio of intraocular pressure to aqueous flow) was decreased 31% ( P < .001). Assuming that AGN 192024 does not cause prolonged lowering of episcleral venous pressure, the results show that pressure-insensitive outflow is enhanced by 50%, whereas tonographic facility of outflow (reciprocal of resistance) was enhanced 35%. CONCLUSIONS: AGN 192024 is an ocular hypotensive agent that works by enhancing both pressure-sensitive and pressure-insensitive aqueous humor outflow without diminishing aqueous humor formation.

Acute effects of H-7 on ciliary epithelium and corneal endothelium in monkey eyes

Purpose. Topical or intracameral administration of H-7 doubles outflow facility and reduces intraocular pressure in cynomolgus monkeys, by relaxing and expanding the trabecular meshwork (TM) and Schlemm’s canal (SC). Since H-7 may have anti-glaucoma potential, we determined its effects on the corneal endothelium and ciliary epithelium for safety considerations. Methods. Following topical H-7, aqueous humor flow (AHF), corneal endothelial transfer coefficient (k a) and anterior chamber (AC) entry of i.v. fluorescein were measured by fluorophotometry; AC aqueous protein concentration ([Protein] AC) was determined by Lowry assay; and corneal thickness and endothelial cell density and morphology were measured by ultrasonic pachymetry and specular microscopy respectively. Following intracameral H-7, specular and/or light and electron microscopy of the corneal endothelium or ciliary epithelium were performed. Results. Following unilateral topical H-7: (1) AHF and k a were essentially unchanged at 0.5–3.0, 3.5–6.0, and 0.5–6.0 hr, with an insignificant increase from 0.5–1.5 hr; (2) [Protein] AC was insignificantly increased at 1–1.5 hr but had returned to baseline by 2.5 hr; (3) entry of i.v. fluorescein into aqueous or cornea was modestly and transiently increased; (4) the central cornea thickened significantly at 1–2.5 hr, gradually returning to baseline 2.5 hr after H-7, while peripheral corneal thickness was less affected; (5) corneal endothelial cell borders became indistinct by 1 hr, but cell morphology was recovering by 3–5 hr and had completely returned to normal by 24 hr; (6) corneal endothelial cell density was unchanged at 5–24 hr. Following intracameral H-7, no significant changes were observed in corneal endothelial cell density or morphology by specular microscopy, nor in corneal endothelial or ciliary epithelial morphology by light and electron microscopy. Conclusions. A facility-effective intracameral dose of H-7 had no discernible structural effect on the corneal endothelium or ciliary epithelium. It is not yet clear whether carefully chosen topical doses of H-7 or analogues can enhance outflow facility without meaningfully affecting the cornea and ciliary processes.

The Failing Filtering Bleb

Blebs fail when the conditions necessary for their continued existence cease to exist. They need a steady flow of aqueous humor to maintain a passageway at the outer edge of the scleral fistula and to distend the interstitial space within the bleb or else connective tissue cells in the episclera and Tenon's capsule may bridge across and fill in those spaces. Initial bleb survival is aided when the flow of aqueous maintains sufficient tissue turgor pressure to collapse the conjunctival and Tenon's capsule blood vessels and when the aqueous is free of inflammatory cells or flare. Under such conditions there is little source of serum-derived growth factors to stimulate fibrosis or vascularization but an adequate nutrient supply to the cells in the bleb. 16

Modulation of Ocular Hydrodynamics and Iris Function by Bremazocine, a Kappa Opioid Receptor Agonist

This study was designed to determine the activity of bremazocine (BRE), a relatively selective kappa opioid receptor agonist, on intraocular pressure (IOP), aqueous humor formation and pupil diameter (PD) in conscious, normal, dark-adapted New Zealand white (NZW) rabbits. IOP was measured in normal and unilaterally sympathectomized rabbits using a calibrated pneumatonometer and the aqueous flow rate was determined by the use of a Fluorotron Master. A masked-design study was conducted in which the rabbits' eyes were treated with BRE topically and unilaterally; the fellow eyes received vehicle. IOP and PD measurements were taken at 0.5hr and 0 time before BRE and 0.5, 1, 2, 3, 4 and 5hr post-treatment. Fluorophotometry recordings were taken at 1hr before and 0.5, 1.5, 2.5 and 3.5hr after topical application of the drug or vehicle. The effect of the relatively selective kappa opioid receptor antagonist, nor-binaltorphimine (nor-BNI), on bremazocine-induced changes in IOP, PD and aqueous flow was also determined. BRE (10 and 100μ g 25μ l−1vehicle) produced dose-related, bilateral reductions in IOP, PD and aqueous humor flow. A large increase in IOP (14mmHg) was observed when BRE (100μ g) was applied to sympathectomized eyes. This ocular hypertensive effect was antagonized when the sympathectomized eyes were pretreated with naloxone (200μ g), a non-selective opioid receptor antagonist. BRE (10 and 100μ g) decreased the aqueous humor flow rate bilaterally by approximately 48 and 60%, respectively, at 0.5hr after administration to the ipsilateral eye. Nor-BNI (100μ g) antagonized the effect of BRE (10μ g) on IOP and aqueous flow rates more effectively than on PD. These data indicate that bremazocine causes reductions in IOP by suppressing aqueous flow, but the ocular hypotensive effects are dependent on the presence of intact sympathetic nerves. Antagonism of BRE's effects on aqueous humor dynamics by nor-BNI suggests that the mechanism of IOP and aqueous flow reduction may involve, in part, an action on kappa receptors. Further experiments are necessary to fully define the opioid receptor populations in the ciliary body.

Pharmacoydnamics of Beta-Blocker Modulation of Aqueous Humor Production

A conscious rabbit model with microdialysis sampling of endogenous aqueous humor ascorbate was developed in order to assess the pharmacodynamics of beta-blocker modulation of aqueous humor production. CMA/20 microdialysis probes were implanted in the anterior chamber of each eye of rabbits (n =6). After a 2 week recovery period, an i.v. bolus of14C-ascorbate (20 μCi) was administered. Blood samples and aqueous humor microdialysis probe effluent were collected and analysed for endogenous and14C-ascorbate to estimate the basal rate of ascorbate blood to aqueous humor secretion (Ro). After a 1 hr washout, each rabbit received a series of three doses of3H-propranolol (750–3000 μ g, 16.5 μCi mg−1) every 60 min into the lower cul-de-sac of each eye. Probe effluent was analysed for endogenous ascorbate and3H-propranolol; ascorbate and propranolol in the iris/ciliary body, vitreous and aqueous was determined at the end of the experiment. Nonlinear least-squares regression analysis of the concentration-time profiles for aqueous humor ascorbate was performed to estimate the change in aqueous humor flow. The average basal aqueous humor ascorbate secretion rate was ∼48 μg hr−1. Propranolol (1500 μg) produced significant increases in aqueous humor ascorbate, this observation is consistent with a reduction in aqueous humor production (∼47%). Analysis of intraocular tissue ascorbate indicated that propranolol inhibited ascorbate secretion at the 3000 μg dose, the highest dose examined in this study; this inhibition was not observed at the 750 μg or 1500 μg doses. Changes in aqueous humor production precipitated by the administration of beta-adrenergic antagonists can be estimated by measuring changes in aqueous humor ascorbate concentrations in the conscious rabbit. Microdialysis sampling of aqueous humor for endogenous ascorbate provides a relevant analytic tool to estimate modulatory effects of anti-glaucoma drugs on aqueous humor production.

Comparison of the efficacy of betaxolol-brinzolamide and timolol-dorzolamide as suppressors of aqueous humor flow in human subjects

ObjectiveTo compare the efficacy of combinations of betaxolol-brinzolamide and timolol-dorzolamide as suppressors of aqueous humor flow and ocular hypotensive agents. DesignPlacebo-controlled, masked comparison of the two drug combinations. ParticipantsTwenty-five normal human volunteers with the fellow eye serving as control. Methods or testingFluorophotometric measurement of aqueous humor flow and pneumatonometric measurement of intraocular pressure. Main outcome measuresAqueous humor flow and intraocular pressure. ResultsThe betaxolol-brinzolamide combination lowered aqueous flow 39% to 44%, and the timolol-dorzolamide combination lowered aqueous flow 51%. The betaxolol-brinzolamide combination lowered intraocular pressure 14% to 19%, and the timolol-dorzolamide combination lowered it 18% to 24%. ConclusionsBoth drug combinations were effective; the timolol-dorzolamide combination appeared to be the more effective of the two after short-term exposure (24 hours).

Combined cycloablation and gonioimplantation for treatment of glaucoma in dogs: 18 cases (1992–1998)

Objective To evaluate a combined cycloablative and gonioimplantation technique for treatment of glaucoma in dogs. Design Retrospective study. Animals 18 adult dogs with glaucoma. Procedure Medical records of dogs that received a valved gonioimplant and a cyclodestructive procedure (cyclocryoablation or diode laser cyclophotocoagulation) during a 6-year period were reviewed. Retention of vision and intraocular pressure control were assessed, as well as number and nature of complications. Results 19 eyes of 18 dogs received a valved gonioimplant and either cyclocryoablation (n = 12) or diode laser cyclophotocoagulation (7). At ≥ 1 year after surgery, 11 of 19 eyes had vision and 14 of 19 eyes had intraocular pressure &lt; 25 mm Hg. Two dogs (2 eyes) were lost to follow-up 3 and 6 months after surgery. Despite the alternative route for aqueous humor flow created by the gonioimplant, 7 eyes had increased intraocular pressure (27 to 61 mm Hg) &lt; 24 hours after surgery. Other complications included excessive intraocular fibrin, focal retinal detachment, corneal ulcer, retinal hemorrhage, cataract, and implant migration. Conclusions and Clinical Relevance Combined cycloablation and gonioimplantation appears to be a promising technique for retention of vision and control of intraocular pressure in dogs with glaucoma. (J Am Vet Med Assoc 1999;215:1469–1472)

Effect of brinzolamide and dorzolamide on aqueous humor flow in human eyes

PURPOSE: To measure the relative efficacy of brinzolamide hydrochloride 1% ophthalmic suspension, a new carbonic anhydrase inhibitor, compared with the currently used dorzolamide hydrochloride 2% ophthalmic solution as suppressors of aqueous humor flow in human eyes, and to study the difference of effect during the day and at night. METHODS: A randomized, double-masked, placebo-controlled study of 25 normal human subjects was carried out at Mayo Clinic. The daytime rate of aqueous humor flow was measured every 2 hours from 8 am to 4 pm by means of fluorophotometry. Likewise, the nighttime rate of aqueous humor flow was measured every 2 hours from 12 am to 6 am. Intraocular pressure was measured at 4 pm and 6 am. RESULTS: Brinzolamide reduced aqueous flow by 0.47 ± 0.20 μl per min (mean ± SD) during the day, whereas dorzolamide reduced flow by 0.34 ± 0.20 μl per min. Brinzolamide reduced aqueous flow by 0.16 ± 0.12 μl per min during the night, whereas dorzolamide reduced flow by 0.10 ± 0.13 μl per min. Brinzolamide reduced afternoon intraocular pressure by 1.5 ± 1.1 mm Hg, and dorzolamide reduced afternoon intraocular pressure by 1.1 ± 1.0 mm Hg. Brinzolamide reduced the morning awakening intraocular pressure by 0.3 ± 1.6 mm Hg, and dorzolamide reduced it by 0.8 ± 1.0 mm Hg. CONCLUSIONS: Our data support the idea that brinzolamide is at least as efficacious as dorzolamide as a suppressor of aqueous humor flow in normal human eyes and that there is probably not a clinically significant difference between the two drugs in this efficacy. Clinicians who prescribe brinzolamide should expect similar ocular hypotensive responses from brinzolamide and dorzolamide.

Immunofluorescence method for quantifying the trabecular meshwork glucocorticoid response (TIGR) protein in trabecular meshwork and Schlemm's canal cells

PURPOSE. Decreased flow of aqueous humor through the trabecular meshwork (TM) and into Schlemm's canal (SC) is believed to be a predominant factor in the development of the elevated intraocular pressure found in primary open-angle and steroid glaucoma. Recent biochemical and genetic evidence has suggested that alterations in the expression of the TM glucocorticoid response (TIGR) protein within the chamber angle may play a role in the development of these glaucomas. To understand the process of TIGR induction in outflow pathway cells we developed an assay for TIGR expression that could distinguish both individual cell responses and also provide a semi-quantitative comparison between cell cultures. The present study demonstrates this approach, using digital image capture of immunofluorescently stained human TM and SC cells after treatment with dexamethasone (Dex). METHODS. Confluent cultures of human TM and SC cells were treated with 1 M Dex or vehicle control for 10 days. The cells were then fixed, permeabilized, and stained using polyclonal antibodies produced against recombinant TIGR. Digital images of fluorescently stained cells, using the same exposure time within an experiment, were evaluated by tabulating the staining intensity of all cells on each image. Between 10 and 40 cells were evaluated per image, 8–10 frames/ sample, 2–3 samples per treatment. Each cell was ranked as either 0 (background), 1+ (minor), 2+ (moderate) or 3+ (very bright staining). RESULTS. TM cells showed a significant basal level of TIGR staining. About 20% of control cells showed appreciable levels of TIGR staining, with intensity levels evenly distributed between 1, 2 and 3+. Dex treatment increased the number of TM cells expressing TIGR to 60–80%, with the majority of cells showing 2+ to 3+ staining throughout the cytoplasm. SC cells showed no basal TIGR staining, but Dex-treated cells exhibited TIGR staining in 6–15% of cells. SC cell TIGR staining varied between 1+ to 2+ in intensity, and showed a distribution different from TM cells. Staining in SC cells was localized to a ribbon-like compartment adjacent to the nucleus. Such perinuclear localization was rarely seen in TM cells. CONCLUSIONS. The low standard errors of the mean TIGR responses within each experiment, and the reproducibility between experiments for each cell type, suggests good reliability for this method. At the same time, the consistent, marked contrast between TM and SC cells in their response to glucocorticoids demonstrates that the assay can distinguish significant differences between cell types. The data support the view that Dex has a cell type specific effect on TIGR induction. The different extent, pattern and localization of TIGR staining between cell types suggests that TIGR expression in SC cells could play a functional role in the outflow pathway, but one that may be distinct from that played in TM cells.

Endothelin-1 effects on aqueous humor dynamics in monkeys.

To report data showing no effect of endothelin-1 on aqueous humor formation and total outflow facility in the cynomolgus monkey, in contrast to the enhancement of outflow facility in monkeys and the suppression of aqueous humor flow in rabbits previously reported by others. Living monkeys received, unilaterally: (i) intracameral endothelin-1 (10 microl bolus, or 2ml or 4ml exchange; final intracameral concentration 1 or 10 nM) with total outflow facility measured for up to 1 hr post-treatment by two-level constant pressure perfusion, and (ii) intravitreal endothelin-1 (20 microl, final intravitreal concentration 0.1 or 1 microM) with aqueous humor flow measured by scanning fluorophotometry for 5 hr starting 12 hr post-treatment. Contralateral eyes received vehicle. Endothelin-1 had no effect on total outflow facility or aqueous humor flow with any of the methods described. Endothelin-1 seems have a variable effect on aqueous humor dynamics within and between species.

Effect of mitomycin C on aqueous humor flow, flare and intraocular pressure in eyes with glaucoma 2 years after trabeculectomy.

The purpose of this study was to determine the intraocular pressure (IOP), aqueous humor flow, flare and ocular side effects in eyes with a history of hypotony after trabeculectomy with adjunctive mitomycin C (MMC). Thirty-six eyes with primary or secondary open-angle glaucoma and IOP < or = 8 mmHg during the postoperative period were studied 745 +/- 315 days after surgery. MMC (0.2 or 0.5 mg/ml) was applied to the episclera with a cellular sponge. Flare was studied with the Kowa Laser Flare Meter 500. Aqueous humor flow was measured in the afternoon (Fluorotron Master II). IOP, visual fields and best corrected visual acuity were also examined. Twenty-two contralateral eyes without surgical intervention served as controls. The mean age of patients was 44.5 +/- 16.8 years. The mean IOP was significantly lower in the MMC group than in the control group: 9.6 +/- 6.4 mmHg vs 18.0 +/- 13.6 mmHg at 2 years (P < 0.001). Aqueous flow was significantly lower in subjects treated with MMC than in controls (P < 0.001). The flare values were significantly higher in the MMC-treated group, with a mean of 12.0 +/- 7.7 photon counts/ms, than in the control group, mean 7.9 +/- 4.6 photon counts/ms (P < 0.019). Our data suggest that MMC is a useful ocular hypotensive agent which seems to participate in a change in aqueous humor dynamics when applied topically as an aqueous solution.

Effect of 8-iso prostaglandin E2 on aqueous humor dynamics in monkeys.

To evaluate the effects of 8-iso prostaglandin E2 (8-iso PGE2; prosta-5,13-dien-1-oic acid,11,15-dihydroxy-9-oxo-,[5Z,8beta-11X,13E,15 S]-) on the intraocular pressure (IOP), outflow facility, and aqueous humor flow rates in normal monkeys and monkeys with glaucoma. The IOP was measured before and as long as 6 hours after the topical application of 8-iso PGE2 to 1 eye of 6 normal monkeys and to the glaucomatous eye of 8 monkeys with unilateral laser-induced glaucoma. The pupil diameter was measured at the same times as the IOP measurements in the normal monkeys. Tonographic outflow facility and fluorophotometric flow rates of aqueous humor were measured in 6 normal monkeys before and after drug treatment. In normal monkeys, a single dose of 0.1% 8-iso PGE2 reduced (P<.01) the IOP for 4 hours in the treated eyes with a maximum (mean +/- SEM) reduction of 3.2 +/- 0.2 mm Hg, compared with the contralateral control eyes. The pupil size was smaller (P<.01) in the treated eyes by as much as 1.0 +/- 0.2 mm for 4 hours. In 8 glaucomatous monkey eyes, the application of 0.05% and 0.1% 8-iso PGE2 reduced the IOP (P<.01) for as long as 2 and 5 hours, respectively. The maximum reduction in the IOP was 4.6 +/- 0.8 mm Hg (0.05%) and 6.0 +/- 0.8 mm Hg (0.1%) compared with baseline measurements. The magnitude and duration of the ocular hypotensive effect were enhanced with twice-a-day administration for 5 consecutive days. Outflow facility in normal monkey eyes was increased (P<.05) by 48% in the treated eyes, and aqueous humor flow was unchanged (P>.10), compared with vehicle-treated contralateral control eyes. Mild eyelid edema, conjunctival edema, hyperemia, and discharge appeared in some eyes treated with the 0.1% drug concentration. The use of 8-iso PGE2 reduces the IOP in both normal and glaucomatous monkey eyes. An increase in outflow facility appears to account for most of the IOP reduction in normal monkeys. The application of 8-iso PGE2 may have potential for the treatment of glaucoma as an outflow facility-increasing drug.

Combined effect of dorzolamide and latanoprost on the rate of aqueous humor flow

PURPOSE: To determine whether latanoprost, an ocular hypotensive agent believed to enhance uveoscleral outflow of aqueous humor, augments the aqueous-suppressing effect of dorzolamide, a topical carbonic anhydrase inhibitor. METHODS: Twenty-four normal subjects underwent measurement of aqueous humor flow by fluorophotometry to determine the flow with placebo, with dorzolamide, and with a combination of dorzolamide and latanoprost. RESULTS: The flow of aqueous humor was suppressed 13% by dorzolamide but not by latanoprost. Latanoprost did not augment the effect of dorzolamide on aqueous humor flow; latanoprost and dorzolamide had additive ocular hypotensive effects. CONCLUSIONS: The uveoscleral flow effect of latanoprost does not improve the aqueous-suppressing effect of dorzolamide, but the two drugs have additive ocular hypotensive effects.

Effect of Latanoprost on the Extracellular Matrix of the Ciliary Muscle. A Study on Cultured Cells and Tissue Sections

Prostaglandin F2αand its analogue latanoprost, both prostanoid FP receptor agonists, reduce the intraocular pressure mainly by enhancing uveoscleral outflow. Changes in the extracellular matrix of the ciliary muscle may be involved in the increased outflow. The effect of latanoprost and prostaglandin F2αon the extracellular matrix of the ciliary muscle was investigated.Cell cultures of human ciliary muscle were treated with latanoprost acid or prostaglandin F2αfor 1–2 days and were immunostained against various extracellular matrix components and metalloproteinases. Proteinases were also analysed by zymography and by measuring plasmin generating ability. For comparison, matrix components were immunolocalized on tissue sections from monkey eyes, treated topically once daily with latanoprost for 10 days.In response to both prostaglandins collagens I, III, and IV, fibronectin, laminin and hyaluronan were reduced, while metalloproteinase -2 and -3 were increased. Zymography demonstrated the presence of functionally active metalloproteinase -2. Both prostaglandins enhanced the generation of plasmin, an activator of metalloproteinases. In the anterior part of the ciliary muscle in latanoprost-treated eyes immunostained collagen VI was decreased in 5 out of 5 monkeys and collagen IV was decreased in 4 of the 5 monkeys.These results suggest a role for latanoprost in the remodeling of extracellular matrix in the ciliary muscle. A latanoprost-induced change in the extracellular matrix might augment the flow of aqueous humour through the ciliary muscle bundles of the uveoscleral pathway.

The effect of dorzolamide on aqueous humor dynamics in normal human subjects during sleep

Objective The purpose of the study was to measure the effect of the topical carbonic anhydrase inhibitor, 2% dorzolamide hydrochloride, on the rate of aqueous humor flow in sleeping humans. Design A randomized, double-masked, placebo-controlled study. Participants Twenty-five normal human subjects. Intervention Topical instillation of 2% dorzolamide hydrochloride versus topical placebo. Main outcome measures Rate of aqueous humor flow in sleeping humans and intraocular pressure immediately after awakening from sleep. Results The rate of flow in sleeping subjects at night (12 am to 6 am) was 1.28 ± 0.30 μl/min (mean ± standard deviation; n = 25) in placebo-treated eyes, whereas the nighttime flow in dorzolamide-treated eyes was 1.17 ± 0.38 μl/min ( P = <0.001), resulting in a nighttime reduction of 9% ( P = 0.032). In contrast, the daytime (8 am to 4 pm) rate of flow in ambulatory subjects was 2.97 ± 0.64 μl/min in placebo-treated eyes and 2.60 ± 0.63 μl/min ( P = 0.032) in dorzolamide-treated eyes, resulting in a daytime reduction of 13% ( P = <0.001). Conclusions Topically administered dorzolamide hydrochloride is effective for reducing the rate of aqueous humor flow in normal human eyes during the day and at night during sleep. The efficacy of dorzolamide at these two times is approximately half that of systematically administered acetazolamide.

A release mechanism for stored ATP in ocular ciliary epithelial cells.

Purines can modify ciliary epithelial secretion of aqueous humor into the eye. The source of the purinergic agonists acting in the ciliary epithelium, as in many epithelial tissues, is unknown. We found that the fluorescent ATP marker quinacrine stained rabbit and bovine ciliary epithelia but not the nerve fibers in the ciliary bodies. Cultured bovine pigmented and nonpigmented ciliary epithelial cells also stained intensely when incubated with quinacrine. Hypotonic stimulation of cultured epithelial cells increased the extracellular ATP concentration by 3-fold; this measurement underestimates actual release as the cells also displayed ecto-ATPase activity. The hypotonically triggered increase in ATP was inhibited by the Cl--channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) in both cell types. In contrast, the P-glycoprotein inhibitors tamoxifen and verapamil and the cystic fibrosis transmembrane conductance regulator (CFTR) blockers glybenclamide and diphenylamine-2-carboxylate did not affect ATP release from either cell type. This pharmacological profile suggests that ATP release is not restricted to P-glycoprotein or the cystic fibrosis transmembrane conductance regulator, but can proceed through a route sensitive to NPPB. ATP release also was triggered by ionomycin through a different NPPB-insensitive mechanism, inhibitable by the calcium/calmodulin-activated kinase II inhibitor KN-62. Thus, both layers of the ciliary epithelium store and release ATP, and purines likely modulate aqueous humor flow by paracrine and/or autocrine mechanisms within the two cell layers of this epithelium.