The effect of prostaglandin inhibitors on the laser-induced disruption of the blood aqueous barrier in the rabbit

In four series, each containing five pigmented rabbits, the therapeutic effects of different anti-inflammatory agents on the laser-induced disruption of the blood aqueous barrier was investigated. Utilizing an argon laser, the peripheral iris of the left eye of each animal was coagulated with a total energy input of 1,000 mJ. The right eyes served as controls. After the coagulation the intraocular pressure was monitored at intervals of 10 min, and the anterior chamber was tapped for analysis of the aqueous humour 100 min after treatement. In a fifth group of five rabbits, aqueous humour was analysed without laser or drug treatment. The protein concentration and the activity of the lactate dehydrogenase were analysed in all samples of aqueous humour. A significant effect on the protection of the blood aqueous barrier could be identified in the eyes pre-treated with indomethacin (2 mg/kg body weight, injected intramuscularly), and in those pre-treated with dexamethasone (12.8 mg/kg body weight, injected intravenously;P < 0.025%). Pre-treatment with aspirin (20 mg/kg body weight, injected intravenously) also had a protective response in the eyes treatet by laser. The significance of the results of clinical treatment is outlined.     

The effect of theophylline on the breakdown of the blood-aqueous barrier in the rabbit eye.

A disruption of the blood-aqueous barrier in rabbit eyes was elicited by topical prostaglandin E2, infrared irradiation of the iris, or subcutaneous alpha-melanocyte stimulating hormone (alpha-MSH). The course of the inflammatory reaction was followed by photoelectrical measurements of the aqueous flare in the anterior chamber. Pretreatment with intravenous theophylline, a phosphodiesterase inhibitor, significantly increased the protein leakage caused by prostaglandin E2 and alpha-MSH, but the response to infrared irradiation was slightly but not significantly enhanced. Intravenous theophylline given in higher doses caused per se an aqueous flare increase, which could not be inhibited by pretreatment with topical indomethacin. Our results indirectly indicate that accumulation of intraocular cAMP promotes a barrier damage and that cAMP might be the common effector of the barrier breakdown caused by prostaglandin as well as by nonprostaglandin agents.     

Fluorophotometry as a method for the detection of permeability changes in the blood and aqueous humor barrier

The increase in permeability of the blood-aqueous barrier after Nd-YAG laser iridotomy and the protective effect of locally applied indomethacin were investigated in an experimental animal study using a computerized fluorophotometer. The permeability of the blood-aqueous barrier was evaluated by three different molecules: fluorescein-sodium (molecular weight 330), fluorescein-labeled dextran 70 000 (molecular weight 70 000) and fluorescein-labeled dextran 150 000 (molecular weight 150 000). The fluorescein concentration of the anterior chamber was measured in 36 eyes (18 rabbits) as well as in a control group of 9 eyes (9 rabbits) at fixed times after intravenous dye injection. Fluorescein leakage occurred, but no leakage of fluorescein-labeled dextrans was visible in the control group. Laser iridotomy induced a time-dependent increase in anterior segment permeability to fluorescein and fluorescein-labeled dextrans. Disturbance of the blood-aqueous barrier was effectively reduced by topical pretreatment with indomethacin, which mainly inhibited the leakage of the fluorescein-labeled dextrans. The clinical relevance of the laser-induced breakdown of the blood-aqueous barrier and the protective effect of a prophylactic pharmacotherapy are discussed.     

Indomethacin and the epinephrine-induced breakdown of the blood-ocular barrier in rabbits

Using aqueous and vitreous fluorophotometry, the authors examined the blood-aqueous and blood-retinal barrier functions in three groups of pigmented rabbits. Epinephrine (1.25%) was applied topically five times daily and indomethacin (0.5% sesame oil suspension) was applied topically three times daily to one eye of each of the animals in Group 1; under the same regimen, epinephrine and indomethacin placebo were administered to one eye of each of the animals in Group 2 and epinephrine placebo and indomethacin placebo were administered to one eye of each of the animals in Group 3. Fluorophotometry was done 1, 2, and 3 months after drug administration. The results showed that epinephrine induced disruption of the blood-aqueous barrier 2 and 3 months after drug administration, and that the magnitude of this disruption increased with time. Epinephrine also induced disruption of the blood-retinal barrier 3 months after drug administration. Indomethacin significantly prevented disruption of the blood-aqueous barrier at 2 and 3 months and significantly prevented disruption of the blood-retinal barrier at 3 months. The magnitudes of the barrier disruptions in eyes treated with both epinephrine and indomethacin were slightly higher than, or the same as, those of the control eyes. The results strongly indicated that the epinephrine-induced disruption of the blood-ocular barrier was partially caused by prostaglandins and other cyclo-oxygenase products whose biosynthesis was initiated by epinephrine.     

Comparison of the effects of corticosteroids and indomethacin on the response of the blood-aqueous barrier to injury

Aqueous protein content was estimated as a measure of the integrity of the blood-aqueous barrier after paracentesis or argon laser photo-coagulation of the iris in rabbits. Corticosteroid pretreatment topically or by subconjunctival or intramuscular injection exerted only a moderate inhibitory effect on the breakdown of the blood-aqueous barrier. Instillation of 0.1% indomethacin however, strongly inhibited the response in both models. The results are indicative of the potential usefulness of topical administration of prostaglandin synthetase inhibitors in the treatment of non-infectious inflammatory diseases.     

Collapse of the blood-aqueous humor barrier following laser injury--preventive pharmacotherapy with prostaglandin inhibitors

Laser-induced collapse of the blood-aqueous barrier and the protective effect of different prostaglandin inhibitors were investigated in the animal study reported here. As a parameter of the barrier function, the protein concentration in the aqueous humor was measured using a micromethod. The anterior chamber of 90 eyes (45 rabbits) was tapped only once, 100 min after the laser procedure. The results prove that different prostaglandin inhibitors in a systemic or topical application form can effectively reduce disturbances of the blood-aqueous barrier after laser surgery. This is also of clinical relevance with regard to laser iridotomy or trabeculoplasty in glaucoma.     

The effect of timolol maleate on the disruption of the blood-aqueous barrier in the rabbit eye

A disruption of the blood-aqueous barrier in rabbit eyes was elicited by use of topical prostaglandin E2(PGE2), infrared irradiation of the iris, or by subcutaneous alpha-melanocyte-stimulating hormone (alpha-MSH). The aqueous flare provoked was measured quantitatively with a photoelectric instrument. The effect of the (topical) beta-adrenergic antagonist timolol maleate on the breakdown of the blood-aqueous barrier was tested. Timolol applied topically in very large doses had no effect on exogenously administered PGE2. However, even in a very small concentration applied topically, timolol reduced the flare response to both infrared irradiation and alpha-MSH. These results support the theory that the effect of alpha-MSH and infrared irradiation on the blood-aqueous barrier is dependent on intact beta-adrenergic receptor sites.     

The role of platelets in blood-aqueous barrier breakdown induced by anterior chamber paracentesis in the rabbit

Anterior chamber paracentesis of the rabbit eye causes disruption of the blood-aqueous barrier, which is characterized by a rapid increase in the albumin and total protein content of the aqueous humor. Prostaglandins appear to be implicated as major mediators in this reaction, since a cyclooxygenase inhibitor, indomethacin, very efficiently prevents protein leakage. When paracentesis was performed in platelet-depleted rabbits (either by transfusion or by treatment with an antiplatelet plasma), the protein content in the aqueous humor did not rise to values observed in normal animals. These data suggest that platelets play some role in the response to paracentesis, a fact in accordance with histological results. In contrast to cyclooxygenase inhibitors, dexamethasone inhibits neither the blood-aqueous barrier breakdown nor prostanoid release from platelets. These data also indirectly indicate the possible role of platelets in triggering the paracentesis reaction in the rabbit.     

Prostanoids in rabbit aqueous humor: effect of laser photocoagulation of the iris

The authors measured concentrations of prostanoids (prostaglandin-like substances) in aqueous humor from normal pigmented rabbit eyes and from those subjected to argon laser photocoagulation of the iris. The predominant prostanoids quantitatively were prostaglandin E2 (PGE2), PGF2 alpha, and PGD2 with minor amounts of 6-keto-PGF1 alpha and thromboxane B2. In all cases, concentrations of prostanoids in laser-treated eyes were substantially greater than those in normal eyes. This finding was particularly striking in the case of PGE2 which increased 60-fold from 87 pg/ml to 5.5 ng/ml after irradiation. Concentrations of prostanoids following photocoagulation were related to the number of administered laser lesions and prostanoid release was associated with an initial hypertensive response and disruption of the blood-aqueous barrier.     

Further investigation into the ocular effects of prostaglandin E2, leukotriene B4 and formyl-methionyl-leucyl phenylalanine

The effect of indomethacin and dexamethasone on the inflammatory response to intraocularly injected prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and formyl-methionyl-leucyl phenylalanine (FMLP) has been examined in rabbits. PGE2, in nanogram quantities, dose-dependently increased intraocular pressure and protein concentration in the aqueous humor. These responses were not affected by an anti-inflammatory dose of dexamethasone, but indomethacin had a small insignificant inhibitory effect. LTB4 and FMLP caused substantial leukocyte accumulation in the anterior chamber and did not disrupt the blood-aqueous barrier. Neither indomethacin nor dexamethasone had any effect on the leukocyte response to LTB4 However, dexamethasone significantly reduced the FMLP-induced leukocyte response. These results suggest that PGE2 and LTB4 do not elicit a further release of AA metabolites and that their actions are direct. However, the chemofactic response of polymorphonuclear leukocytes to FMLP appears to be mediated by lipoxygenase products.     

Ocular effects of endothelin-1 in the cat.

The effects of intravitreal and intracameral administration of endothelin-1 were studied in the anaesthetized cat. Intravitreal injection of 0.4 nmol endothelin-1 induced a 34 +/- 10% (n = 5; P less than 0.05) reduction in retinal blood flow in the experimental eye compared to the control eye 80 minutes after the injection. Blood flow in the ciliary body, iris and choroid remained unaffected by the injection of endothelin-1. Intracameral administration of endothelin-1 at pmol doses caused a reduction in pupil size, an increase in the aqueous humor protein concentration (indicating a break-down of the blood-aqueous barrier) and an increase in the concentration of prostaglandin E2 in the aqueous humor. The effect of endothelin-1 on pupil size was abolished by indomethacin pretreatment, indicating that this effect was mediated by arachidonic acid metabolites.     

Prostaglandin E in rabbit aqueous humor after Nd-YAG laser photodisruption of iris and the effect of topical indomethacin pretreatment.

Ocular changes (prostaglandin E, protein, pupil diameter, and intraocular pressure) induced by photodisruption of pigmented rabbit iris with neodymium-yttrium aluminum garnet (Nd-YAG) laser and the effect of topical indomethacin upon those changes were examined. Concentrations of prostaglandin E in laser-treated eyes (1,3,5,10, and 20 lesions) were substantially greater than those in normal eyes and were associated with an initial hypertensive response. This finding was particularly striking in the case of 20 lesions. In that case, concentrations of prostaglandin E increased 50-fold, from 99 pg/ml of control level to 5049 pg/ml 60 min after irradiation. Disruption of blood aqueous barrier measured by protein concentration, changes in intraocular pressure, and pupil diameter occurred at a similar dose range of laser application. Concentration of protein and changes in pupil diameter already were prominent at 15 min after laser treatment, and changes in intraocular pressure were prominent at 60 min. Indomethacin pretreatment abolished most of these responses, suggesting that acute reactions following photodisruption largely depended on prostaglandin synthesis in iris tissue.     

Studies on the Blood-Aqueous Barrier after Argon Laser Photocoagulation of the Iris

Breakdown and re-establishment of the blood-aqueous barrier (BAB) was studied following laser irradiation to the rabbit iris by quantitating leakage of protein, fluorescein, and fluorescein-labeled dextran (FLD-70, MW 70,000) into the aqueous humor. Breakdown of the BAB was more prolonged in pigmented than albino animals, possibly due to the increased laser energy absorbed by the pigmented iris. Fluorophotometry appeared to be a more sensitive method for evaluating BAB breakdown than aqueous protein measurements, and small molecule leakage (fluorescein) appeared to be more sensitive than macromolecule leakage (FLD-70). The noninvasive method of evaluating the BAB proved equally as effective as measuring aqueous protein content in assessing the sensitivity of laser-induced trauma to the ameliorating effect of the nonsteroidal anti-inflammatory agent indomethacin.     

Role of Tromaril as anti-prostaglandin drug on blood aqueous barrier

In this experimental work, it was observed that after anterior chamber paracentesis there was more effusion of protein into the anterior chamber. Pretreatment with aspirin/indomethacin and a new drug, enfenamic acid (Tromaril), decreased this trauma-induced increase in aqueous protein content. It was further observed that this inhibition was more marked with Tromaril pretreatment in comparison with other drugs. Prostaglandin-mediated disruption of blood aqueous barrier can also be decreased with Tromaril pretreatment. Tromaril, a prostaglandin synthetase inhibitor, may help us to control the reactions to surgical ocular trauma and other ocular inflammatory diseases.     

Ocular inflammatory responses in the EP2 and EP4 receptor knockout mice

Purpose: To examine the role of EP2 and EP4 receptors in murine ocular inflammation. Methods: Prostaglandin EP2 and EP4 receptor knockout and wild-type mice were treated topically with prostaglandin E2, SDF-1, and RANTES and lipopolysaccharide by intravitreal injection. Paracentesis was performed by puncturing the cornea. The increase in the level of aqueous humor protein and the number of leukocytes were measured and the vascular leakage of protein was visualized using fluorescein angiography. Results: In the EP2 receptor knockout mice, there was significant inhibition of the disruption of the blood-aqueous barrier caused by lipopolysaccharides, paracentesis, prostaglandin E2, SDF-1, and RANTES. Reductions in the disruption in the blood-aqueous barrier and leukocyte infiltration after lipopolysaccharide injection and paracentesis were significant, but there was no increase in the aqueous humor protein level after prostaglandin E2 treatment in EP4 receptor knockout mice. Conclusions: The results of the present experiments suggest that EP2 and EP4 receptors partly mediate the disruption of the blood-aqueous barrier and leukocyte infiltration induced by prostaglandin E2, SDF-1, RANTES, and lipopolysaccharides.     

Blood-aqueous barrier in eyes with retinal vein occlusion.

PURPOSE: The purpose of this study is to examine the changes of blood-aqueous barrier function in cases of central or branch retinal vein occlusion. METHODS: In addition to fluorophotometry of the aqueous humor and posterior vitreous, the authors used a method that quantifies protein in the aqueous (aqueous flare) by measuring the intensity of scattered laser light. RESULTS: Aqueous and posterior vitreous fluorescein concentrations and aqueous flare were significantly higher than in unaffected fellow eyes or eyes of visually normal age-matched controls both in central and branch retinal vein occlusions. They also were significantly higher in eyes with central vein occlusion than in those with branch vein occlusion. Among those eyes with central vein occlusion, aqueous and posterior vitreous fluorescein concentrations and aqueous flare were significantly higher in the hemorrhagic than in the venous stasis type of disease. Among eyes with branch vein occlusion, cases at the acute stage showed significantly higher amounts of aqueous and posterior vitreous fluorescein concentrations and aqueous flare than did those with chronic occlusion. CONCLUSION: The authors believe that increased amounts mainly reflect blood-ocular barrier disruption. Not only the blood-retinal barrier but also the blood-aqueous barrier disruption is a common sequela in the disorder.     

The time course of laser-induced disruption of the blood aqueous barrier in the rabbit

The response of the blood aqueous barrier to a defined laser trauma was investigated in a series of seven groups with three pigmented rabbits in each group. The peripheral iris of the left eye was treated with the Argon laser (ten spots of 50-m size with an energy of 100 mJ). The right eyes served as controls. The anterior chambers of both eyes were tapped at given time intervals after the laser coagulation to enable the analysis of the protein content of the aqueous humour and for the assay of the lactate dehydrogenase activity. Within 100 min after laser treatment a positive correlation between time and protein concentration in the anterior chambers of the treated eyes (r = 0.77) and in the untreated eyes (r = 0.79) was established. There was a significant response on the blood aqueous barrier in the untreated fellow eyes. The activity of the lactate dehydrogenase showed a significant increase 5, 70 and 100 min after laser trauma in the treated eyes only. The laser trauma induced a significant increase ( = 0.01) in the intraocular pressures of the treated eyes, which persisted up to 70 min after treatment. The clinical implications of these findings are discussed.     

Effects of calcitonin gene-related peptide in the eye. A study in rabbits and cats

Calcitonin gene-related peptide (CGRP) has recently been demonstrated in sensory neurons of the eye. The purpose of the present study was to determine the effects of exogenous CGRP in the rabbit and cat eye. CGRP was injected intracamerally and the intraocular pressure was measured in cannulated eyes. The pupil diameter and the aqueous humor protein concentration were also measured. Indomethacin was used to prevent prostaglandin synthesis and tetrodotoxin (TTX) to block nerve conductance. In the rabbit eye, CGRP caused iridial hyperemia, a breakdown of the blood-aqueous barrier and increased intraocular pressure. These responses were dose-related. The increase in IOP as well as the breakdown of the blood-aqueous barrier could not be blocked with TTX or indomethacin. In cats CGRP caused a decrease in IOP and had only slight effect on the aqueous humor protein concentration. Neither in rabbits nor in cats had CGRP any detectable effect on the pupil size. Intracameral injection of 0.1 microgram (7.4 x 10(-11) moles) substance P together with 0.1 microgram (2.6 x 10(-11) moles) CGRP in rabbits caused maximal miosis but did not potentiate the intraocular effects of CGRP only. These results indicate that CGRP has marked vascular effects in the rabbit eye, causing a breakdown of the blood-aqueous barrier and increased IOP. The mechanism of this phenomenon does not involve prostaglandins neither nerve conduction, implying most likely a direct effect on the vascular smooth muscle. The mechanism of the decrease of IOP in cats remains unknown.     

Disruption of the blood-aqueous barrier following paracentesis in the rabbit

The concentrations of protein and prostaglandin are greatly elevated in aqueous humour secondary to anterior chamber paracentesis in the rabbit. A transient increase of intraocular tension which follows paracentesis is mediated by prostaglandin and the breakdown in the blood-aqueous barrier is at least partly mediated by this autacoid. Using a fluorescein angiographic technique the bulk of the plasmoid aqueous was shown to enter the anterior chamber through the pupil and not from the surface of the iris. Furthermore, the capillary beds of the ciliary processes, but not of the iris, took up intravenously-injected colloidal carbon indicating that the ciliary vessels became excessively permeable. The present evidence indicates that the site of disruption of the blood-aqueous barrier occurs within the ciliary processes and not in the iris.     

The effect of experimental uveitis on the uptake of prostaglandin E1 in the rabbit iris-ciliary body

Disruption of the blood-aqueous barrier in rabbits was elicited by infrared irradiation of the iris or by alpha-melanocyte stimulating hormone (alpha-MSH) given subcutaneously. One group of animals was pretreated with topical imidazole before the injection of alpha-MSH. The aqueous flare response was followed and the rabbits were killed at the expected height of the uveitis. The uptake of 3H-prostaglandin E1 in the iris with the ciliary body was then determined and found to be significantly decreased in the rabbits in which alpha-MSH had caused a severe damage of the blood-aqueous barrier. When alpha-MSH caused a more moderate aqueous flare response the prostaglandin uptake was on the contrary significantly increased. Pretreatment of the animals with topical imidazole enhanced parallelly the prostaglandin uptake and the aqueous flare response to alpha-MSH. Topical imidazole per se was found to increase the accumulation of prostaglandin. The prostaglandin uptake values were, however, unchanged in eyes in which infrared irradiation of the iris induced a moderate flare response.