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.     

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.     

Interaction of adrenergic agents with alpha-melanocyte-stimulating hormone and infrared irradiation of the iris in the rabbit eye.

Breakdown of the blood aqueous barrier in the rabbit eye induces a protein leakage into the aqueous humor, seen as a flare in the anterior chamber. A barrier damage was induced by topical prostaglandin E2(PGE2), infrared irradiation of the iris, or alpha-melanocyte-stimulating hormone (alpha-MSH) given subcutaneously. The aqueous flare was measured quantitatively by means of a photoelectric instrument. The interference of adrenergic antagonists and agonists on the breakdown of the barrier was tested. The alpha-adrenergic antagonist phentolamine and the beta-adrenergic antagonist propranolol, given intravenously, had no effect on exogenously administered PGE2, but both antagonists reduced the flare response to infrared irradiation which is supposed to exert its effect via endogenous prostaglandin release. The alpha-MSH response was unaffected by phentolamine, whereas propranolol abolished the flare response to alpha-MSH totally. The PGE1 response was unaffected both by the alpha-adrenergic agonist noradrenaline and the beta-adrenergic agonist terbutalin sulfate, administered topically. Noradrenaline, however, inhibited the flare response to infrared irradiation and facilitated the flare response to alpha-MSH. Terbutalin sulfate worked synergistically with both infrared irradiation and alpha-MSH. It is assumed that alpha-MSH exerts its effect on the barrier via enhanced beta-adrenergic activity, whereas the effects caused by infrared irradiation seem conditioned by intact alpha- as well as beta-adrnergic receptor sites.     

Capsaicin pretreatment prevents disruption of the blood-aqueous barrier in the rabbit eye

Capsaicin, the irritating agent of red pepper, produces ocular inflammation through a neurogenic mechanism. The present study is concerned with the long-term effects of capsaicin pretreatment on the capacity of the eye to respond to different inflammatory stimuli. Following retrobulbar injection of capsaicin to rabbits the aqueous flare response induced by subsequent infrared irradiation (IR) of the iris, subcutaneously administered alpha-melanocyte-stimulating hormone (alpha-MSH) and exogenously administered prostaglandin E2 (PGE2) was reduced greatly. In the case of IR and alpha-MSH the reduced responsiveness was manifest for several weeks after capsaicin pretreatment, involving first the capsaicin-treated eye, but later also the contralateral control eye. After 2-3 months the aqueous flare response was normal in both eyes. In the case of PGE2 the responsiveness was reduced for a shorter time; after 3 weeks the response was normal in both eyes. The results indicate that all three stimuli tested are at least partly dependent upon an intact sensory innervation to disrupt the blood-aqueous barrier, but that the mechanism of action of PGE2 is different from that of IR and alpha-MSH.     

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.     

The effect of polyphloretin phosphate on the aqueous flare response to alpha-melanocyte stimulating hormone

The breakdown of the blood aqueous barrier caused by topical prostaglandin E1 (PGE1), prostaglandin E2 (PGE2) or subcutaneous alpha-melanocyte stimulating hormone (alpha-MSH) was quantified by measurements of the aqueous flare seen in the anterior chamber. Polyphloretin phosphate (PPP) administration subcutaneously was found to effectively block the protein leakage caused by all three traumatic stimuli. The same dose of PPP given intravenously inhibited effectively the flare response to PGE1 and alpha-MSH, whereas the effect of PGE2 was only slightly decreased. Significant inhibition by subconjunctival PPP was not achieved for any of the three stimuli. Assuming that PPP is a specific PG-antagonist the present results support the eariler suggestion that PGs take part in the barrier damaging action of alpha-MSH. However, it cannot be excluded that PPP acts on a step subsequent to PG. This step might be common to PGs- and alpha-MSH-effects on the barrier, explaining why PPP inhibits both types of trauma.     

The effects of 3-isobutyl-methyl-xanthine on experimentally induced ocular inflammation in the rabbit

The effect of topical administration of 3-isobutyl-methyl-xanthine (IBMX), a potent phosphodiesterase inhibitor, was studied on an experimentally provoked uveitis in rabbits. After presensitization with an intravitreal injection of human serum albumin (HSA), intravenous antigenic challenge induces blood-aqueous barrier breakdown and leukocyte infiltration. The effect of IBMX on the blood-aqueous barrier was determined by scoring the severity of the flare in the anterior chamber and by determination of the levels of ascorbic acid and protein in the aqueous. Treatment with IBMX 1% two times daily, significantly inhibited the breakdown of the blood-aqueous barrier and the increase in PGE2 level of the aqueous humor. There was no effect on leukocyte infiltration. The therapeutic effect of IBMX in blood-aqueous barrier protection is comparable with the effect of topical treatment with the corticosteroid medrysone.     

The effect of topically applied prostaglandin inhibitors on the laser-induced disruption of the blood aqueous barrier

The therapeutic effect of topically applied prostaglandin inhibitors on the laser-induced disruption of the blood-aqueous barrier was investigated in six series of five rabbits each. One series was not coagulated and served as baseline, and in a reference group laser coagulation was performed without pretreatment with a prostaglandin inhibitor. In four series the iris laser coagulation of the left eyes was preceded by topical application of a prostaglandin inhibitor. The right eyes served as controls for the contralateral effect on the blood aqueous barrier. After laser coagulation the intraocular pressure was monitored at 10-min intervals, and the anterior chamber was tapped for analysis of the protein concentration and the lactate dehydrogenase activity. Pretreatment with dexamethasone eyedrops and indomethacin eyedrops markedly blocked the laser-induced disruption of the blood-aqueous barrier. The level of protein concentration in the aqueous humor after laser coagulation was much less after pretreatment with dexamethasone or indomethacin eyedrops. The effect was significant, both for the laser-treated eyes and for the noncoagulated fellow eyes (p < 0.025). The subconjunctival pretreatment with dexamethasone 1 or 24 h before laser coagulation had no significant effect with respect to the protection of the blood aqueous barrier.     

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.     

超声乳化白内障吸除术对血-房水屏障功能的影响

目的　观察小切口超声乳化白内障吸除人工晶状体植入术及相关因素对血 房水屏障功能的影响。方法　使用激光蛋白细胞检测仪对 60例 (64只眼 )白内障患者超声乳化白内障吸除人工晶状体植入术前、后的房水蛋白浓度进行定量检测 ,记录并比较闪光值。术后随访时间为 3个月。结果　超声乳化白内障吸除人工晶状体植入术前 ,术后 1d、1周、1个月及 3个月术眼房水的平均闪光值分别为 (6 94± 0 3 4 )、(2 6 2 7± 1 3 7)、(13 96± 1 0 5)、(9 0 7± 0 43 )及 (7 16± 0 2 7)光粒子数 /ms ,其中术后 1d、1周及 1个月高于术前 ,且差异均有显著意义 (P <0 0 5) ;术后 3个月与术前比较 ,差异无显著意义 (P >0 0 5)。术后早期术眼房水蛋白浓度与患者年龄呈正相关 (r =0 40 0 ,P =0 0 0 1) ,与患者的性别和眼别均无相关。术中虹膜脱出者术后 1d和 1周血 房水屏障功能破坏严重。结论　超声乳化白内障吸除人工晶状体植入术在术后短期内影响术眼的血 房水屏障功能 ;激光蛋白细胞检测仪可动态评价超声乳化白内障吸除术对血 房水屏障功能的影响。 (中华眼科杂志 ,2 0 0 4,40 :2 6 2 9)     

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.     

Nicardipine inhibits acute rise of aqueous flare and intraocular pressure induced by argon laser photocoagulation

The purpose of this study was to examine the anti-inflammatory effect of the calcium channel blocker nicardipine. Intraocular inflammation was induced by argon laser photocoagulation of the iris of pigmented rabbits and was assessed by measuring aqueous flare and intraocular pressure. This resulted in a marked increase in the aqueous flare that peaked at approximately one hour following coagulation and returning to the original values after six hours. Intraocular pressure increased within 15 minutes following laser treatment and returned to baseline levels at 60 minutes. Pre-treatment of the rabbits with an intravenous injection of 2 mg/kg of nicardipine completely abolished both the increase in aqueous flare and intraocular pressure induced by laser photocoagulation as compared to the control experiment. Earlier work from the author's group has shown that nicardipine can also block aqueous flare and intraocular pressure increases induced by topical administration of prostaglandin E2. From these combined experiments they would like to draw the conclusion that the inflammatory reaction induced by photocoagulation of the iris is partly mediated by prostaglandins and that blockade of calcium channels by nicardipine can inhibit the effects induced by prostaglandin E2.     

The effects of forskolin on cyclic AMP, intraocular pressure and aqueous humor formation in rabbits

Forskolin was used to study cyclic AMP-mediated regulation of aqueous humor dynamics in rabbits. Crystalline forskolin was solubilized in oil and its pharmacological effects were studied both in vitro and following topical ocular administration. In vitro, using cultured corneal epithelial cells, forskolin rapidly stimulated cyclic AMP production and in vivo increased cyclic AMP concentration in the aqueous humor 10-fold following topical administration. The effect of topical forskolin on intraocular pressure and aqueous humor formation was determined in vivo using pneumatonometry and fluorophotometry, respectively. Forskolin caused a prolonged reduction of intraocular pressure and decreased aqueous humor formation. The ability of forskolin to potentiate the ocular hypotensive effect of epinephrine was investigated. Forskolin in combination with epinephrine caused a decrease in intraocular pressure of longer duration than either 0.1% epinephrine or 1% forskolin administered separately. Forskolin caused a small but significant increase in the permeability of the blood-aqueous barrier at the time of maximal intraocular pressure reduction. This effect on the blood-aqueous barrier may explain the inhibitory effect of forskolin on aqueous humor formation.     

Serum albumin enters the posterior chamber of the eye permeating the blood-aqueous barrier

In order to check the entrance site of serum albumin into the aqueous humor, rabbits were injected intravenously either with Evans blue (which reacts very quickly with albumin) or horseradish peroxidase. The Evans blue-albumin complex (Eb-a) was traced to the posterior chamber as early as I min after injection by examining frozen half eyes. The Eb-a was localized in frozen sections by fluorescence microscopy in the stroma of the ciliary and iridial processes, as well as in the lumen of all blood vessels from 1 to 60 min after injection even at doses as low as 3 mg/kg. The peroxidase activity was also localized on these same structures from 8 min to 4.5 h. Neither tracer was visualized in the iris stroma outside the lumen of blood vessels. This was also true for experiments with Eb (75 mg/kg) in which the blood-aqueous barrier was disrupted. The concentration (m/v) of Evans blue and the peroxidase activity in the aqueous humor of the anterior chamber were estimated by spectrophotometry. The morphological integrity of the blood-aqueous barrier was demonstrated by electron microscopy in all peroxidase-injected rabbits. Considering that (a) the Eb-a appeared first in the posterior chamber, (b) there was a high concentration of tracers in the stroma of the ciliary and iridial processes, (c) neither tracer was visualized in the iris stroma, (d) there was no evidence of disruption of the blood-aqueous barrier, and (e) the concentration of both tracers in the aqueous humor kept increasing up to 4 h after injection, it was assumed that serum macromolecules entered first the posterior chamber and subsequently migrated to the anterior chamber. Most likely they passed in between the cells of the inner layer of the ciliary epithelium, the site of the so-called blood-aqueous barrier. No evidence was found indicating migration of macromolecules from the stroma of the processes directly to the anterior chamber via the iris root.     

CGRP in relation to neurogenic inflammation and cAMP in the rabbit eye

The effects of topical application of neutral formaldehyde (1%) and intracameral administration of calcitonin gene-related peptide (CGRP, 0.5- or 2.0 micrograms) on the intraocular pressure (IOP), blood-aqueous barrier, pupil size, blood pressure and cyclic AMP (cAMP) content in the aqueous humour of a rabbit were studied. Topical chemical irritation with 1% formaldehyde caused a typical irritative response in the eye with a rise in the IOP, breakdown of the blood-aqueous barrier and miosis. The cAMP content in the aqueous humour was also increased (88.5 +/- 35.0 pmol ml-1, P less than 0.05) when compared with the control group (16.3 +/- 3.6 pmol ml-1). Intracameral administration of CGRP caused a rise in the IOP, breakdown of the blood-aqueous barrier and also systemic hypotension. Miosis was not observed after intracameral CGRP but an increase in the cAMP content in the aqueous humour was seen (130.5 +/- 30.3- and 158.7 +/- 48.1 pmol ml-1, both P less than 0.01, after 0.5 or 2.0 micrograms, respectively). The cAMP concentration in the aqueous humour after topical chemical irritation and intracameral CGRP correlated with the intensity of the breakdown of the blood-aqueous barrier. CGRP seems to cause most, but not all, of the ocular changes after sensory nerve stimulation elicited by topical neutral formaldehyde. Of these CGRP-induced changes, only the breakdown of the blood-aqueous barrier is related to an increase in the cAMP content in the aqueous humour. Contralateral responses after sensory nerve stimulation were similar to contralateral responses to intracameral CGRP.     

Efficacy of low concentrations of ketorolac tromethamine in animal models of ocular inflammation.

PURPOSE: To determine if topical ophthalmic application of ketorolac tromethamine concentrations below 0.5% can block the biochemical and physiological processes associated with chemically induced ocular inflammation in rabbits. METHODS: Ocular inflammation was induced in rabbits by intravenous (i.v.) injection of endotoxin (2.5 microg/kg) isolated from Salmonella typhimurium, or by a topical application of arachidonic acid (1.0%). The effect of ketorolac (at concentrations ranging from 0.001%-0.5%) on ocular inflammation was determined by measuring changes in the blood-aqueous barrier, using fluorophotometry (dextran-isothiocyanate-fluorescein; FITC-dextran 2%) and by measuring changes in aqueous humor protein concentrations. Changes in aqueous humor prostaglandin E(2) (PGE(2)) concentrations were also measured. RESULTS: Ketorolac 0.01%-0.5% produced substantial decreases in endotoxin-induced fluorescein leakage into the aqueous humor. The decrease produced by ketorolac 0.1% was comparable to that produced by ketorolac 0.5%. Ketorolac 0.1%-0.5% produced substantial decreases in endotoxin-induced increases in prostaglandin concentrations in the aqueous humor, and in arachidonic acid-induced protein leakage into the aqueous humor. CONCLUSIONS: Topical application of ketorolac concentrations as low as 0.01%-0.1% significantly reduce chemically induced ocular inflammation in rabbits.     

Effects of prostaglandin E2 on intraocular pressure, anterior chamber depth and blood flow volume of the iris and the ciliary body in rabbit eyes]

The effects of prostaglandin E2 (PGE2) on intraocular pressure (IOP), anterior chamber depth, and blood flow volume of the iris and the ciliary body of albino rabbits were investigated. Swelling and marked capillary dilatation of the ciliary body were observed after topical application of PGE2. IOP increased immediately by 200 micrograms, 400 micrograms, and 1,000 micrograms of PGE2, reached a peak within 30 minutes; then decreased gradually. The anterior chamber depth decreased only at 5 and 10 minutes after 1,000 micrograms of PGE2. The blood flow volume of the iris and the ciliary body immediately increased, and kept it up for 3 hours. Changes of IOP may be associated with an increase of blood flow attendant upon capillary dilatation of the ciliary body, and an increase of aqueous outflow due to breakdown of the blood-aqueous barrier. In addition to morphological and functional changes of the ciliary body, further factors which promote vitreous volume expansion may play an essential part in the development of malignant glaucoma.     

Effects of tetramethylpyrazine on prostaglandin E(2)- and prostaglandin E(2) receptor agonist-induced disruption of blood-aqueous barrier in pigmented rabbits

PURPOSE: To evaluate the effect of tetramethylpyrazine on the elevation of aqueous flare and intraocular pressure (IOP) induced by prostaglandin (PG) E(2) and PGE(2) receptor (EP) agonists. METHODS: PGE(2) or EP agonists (11-deoxy PGE(1), EP(2) agonist; 17-phenyl trinor PGE(2), EP(1) and EP(3) agonist; or sulprostone, EP(1) and EP(3) agonist), 25 microg/mL, were transcorneally administered to pigmented rabbits. Animals were pretreated with tetramethylpyrazine intravenously (10 or 30 mg/kg) or topically (0.1% solution). Aqueous flare was measured using a laser flare-cell meter, and the intensity was expressed as the area under the curve (AUC). Intraocular pressure was measured using a noncontact tonometer. RESULTS: After administration of PGE(2), aqueous flare and IOP increased and then gradually decreased. The AUC of eyes pretreated with tetramethylpyrazine, 10 or 30 mg/kg, intravenously, or topical 0.1% solution, was significantly smaller than that of the controls. The mean Delta IOP of eyes pretreated with tetramethylpyrazine, 30 mg/kg intravenously, was significantly lower than that of the controls. After administration of 11-deoxy PGE(1), aqueous flare increased and then gradually decreased. 17-phenyl trinor PGE(2) and sulprostone did not disrupt the blood-aqueous barrier. The AUC of eyes pretreated with tetramethylpyrazine, 10 or 30 mg/kg, intravenously, before 11-deoxy PGE(1) application was significantly smaller than that of the controls. CONCLUSION: The results indicated that tetramethylpyrazine inhibited PGE(2)- or 11-deoxy PGE(1)-induced elevation of aqueous flare and IOP.     

Changes in anterior chamber flare and cells following cataract surgery.

The laser flare cell meter allows rapid non-invasive quantification of aqueous flare and cells. In this prospective study laser photometry was used to document the recovery of the blood-aqueous barrier in 27 normal eyes following cataract surgery. Aqueous flare and cells were highest on the first postoperative day, declining rapidly in the first week and returning to preoperative levels by 3 months. In six eyes (22.2%) there was an increase in either flare and cells or flare alone during the first postoperative week which was associated with a delayed recovery of the blood-aqueous barrier for up to 1 month following surgery. A consensual flare response was found to occur in the fellow eye in five patients (18.5%).     

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.