Prostanoid receptor gene expression profile in human trabecular meshwork: a quantitative real-time PCR approach.

PURPOSE: To assess the expression pattern of prostanoid receptor-encoding genes in trabecular meshwork (TM) of human donor eyes. METHODS: Disposed human donor eyes (n = 10) were obtained from the Cornea Bank, Amsterdam. The TM was dissected from the scleral tissue and homogenized in lysis buffer, and total RNA was isolated. The RNA was converted into cDNA and used as a template for noncompetitive quantitative real-time polymerase chain reaction (PCR) using green fluorescent dye to quantify the accumulation of double-stranded PCR product. Specific primers for four housekeeping genes and DP, EP(1), EP(2), EP(3,) EP(4), FP, IP, and TP receptor-encoding transcripts were developed and tested for their efficiency. RESULTS: The characterized expression profile was highly reproducible in all samples, with the EP(2) receptor-encoding transcript in the highest abundance, followed by FP, TP, IP, and EP(4) at levels that were approximately 10 to 15 times lower than that of the EP(2) subtype. DP and EP(3) were at the lowest levels, which were, on average, 45 times and 228 times lower than EP(2), respectively. CONCLUSIONS: These data show that all prostanoid receptors are expressed at different levels in human TM tissue. Because the gene expression of the EP(2) receptor is, on average, 15 times more abundant than that of the EP(4) receptor, it may be expected that the increase in flow and cAMP levels in response to the activation of the EP receptors by application of prostaglandin E(1) (PGE(1)), is primarily mediated by the EP(2) receptor. These data should be considered when designing prostanoid receptor mimetics intended to enhance the aqueous humor outflow through the TM and Schlemm's canal.

Pharmacological therapy for glaucoma: a review.

For some time the medical treatment of glaucoma has consisted of topical beta-blockers, adrenergic agents, miotics and oral carbonic anhydrase inhibitors (CAIs). However, the therapeutic arsenal available for the medical treatment of glaucoma has recently extended with new classes of ocular hypotensive agents i.e. prostaglandins, local CAIs and alpha2-adrenergic agents. Beta-blockers are still the mainstay in glaucoma treatment and are first line drugs. However, even if they are applied once daily, as with timolol in gel forming solution and levobunolol, the possible cardiopulmonary adverse effects of beta-blockers remain a cause for concern. When monotherapy with beta-blockers is ineffective in reducing intraocular pressure (IOP) or is hampered by adverse effects, a change of monotherapy to prostaglandins, local CAIs, alpha2-adrenergic agonists (brimonidine) or to dipivalyl epinephrine is advised. Prostaglandins, local CAIs and alpha2-adrenergic agonists, such as brimonidine, may in time become first line drugs because they reduce IOP effectively and until now systemic adverse effects have rarely been reported with these agents. The development of a pro-drug of either a local CAI or an alpha2-adrenergic agonist with a sustained and continuous effect on IOP level, which could be applied once a day is suggested. Because of these new developments, miotics, i.e. pilocarpine and carbachol, are recommended as second or third line drugs. The cholinesterase inhibitors are considered third line drugs as better agents with fewer local and systemic adverse effects have become available. Oral CAIs may be used temporarily in patients with elevated IOPs e.g. postsurgery or post-laser, or continuously in patients with glaucoma resistant to other treatment. Combining ocular hypotensive drugs is indicated when the target pressure for an individual patient cannot be reached with monotherapy. Combination therapy of beta-blockers is additive with prostaglandins, topical CAIs and miotics. Prostaglandins such as latanoprost can be combined with beta-blockers, adrenergic agents, local CAIs and miotics. Combinations with brimonidine or local CAIs need further investigation. Treatment of glaucoma with the new ocular hypotensive agents, either in monotherapy or combination therapy, may provide lower IOPs and delay or postpone the need for surgery.

Rate of visual field loss in progressive glaucoma.

OBJECTIVE: To investigate the rate of visual field (VF) loss in progressive glaucoma. SETTING: Outpatient department, nonreferral base. METHODS: A cohort of 34 patients with normal-pressure glaucoma (NPG), 68 patients with primary open-angle glaucoma (POAG), and 125 patients with ocular hypertension (OHT) were followed up for an average of 9 years. Visual fields were obtained annually with automated perimetry. The rate of VF loss as a percentage per year was calculated. RESULTS: Twenty-three eyes with NPG, 31 with POAG, and 10 with OHT showed progression of VF loss. The mean (+/-SD) rates of VF deterioration were 3.7%+/-3.3% per year in NPG, 2.5%+/-1.8% in POAG, and 2.3%+/-1.3% in OHT converting to POAG, and did not differ significantly. No difference in the rate of VF loss was found between eyes with and without optic disc hemorrhages (2.7%+/-2.9% and 3.1%+/-2.1%, respectively). The rate of VF loss was not related to the initial VF status. The rate of VF loss between the superior and inferior hemifields was correlated in patients with NPG (r(s) = 0.67, P = .04). Comparison of visual field loss with linear regression analysis showed significant slopes in only 37.5% of eyes with progression, which had a progression rate of 4.2%+/-3.0%. CONCLUSIONS: The rate of VF loss did not differ between patients with NPG and POAG. The rate of deterioration was related neither to initial VF status nor to the presence of disc hemorrhages. Linear regression is applicable only in a portion of the patients who have progression of VF loss.

Flow after prostaglandin E1 is mediated by receptor-coupled adenylyl cyclase in human anterior segments.

PURPOSE: To assess the effect of prostaglandin (PG) F2alpha and PGE1 on flow through the trabecular meshwork in organ preserved human anterior segments. METHODS: Isolated human anterior segments were perfused under standard conditions at a constant pressure of 10 mm Hg, while flow was continuously monitored. After a stabilization period, 6 consecutive concentrations of PGs were administered. cAMP levels were determined in the perfusate at baseline conditions and at 10(-6) M PG. RESULTS: Perfusion with concentrations ranging from 10(-10) to 10(-5) M PGE1 resulted in a dose-dependent increase in flow (P < 0.0001), reaching a plateau of a 26% increase at 10(-7) M. Perfusion with PGF2alpha or placebo (Eagle's minimum essential medium) did not influence baseline flow. cAMP produced by human anterior segments increased from 4.8+/-0.6 pmol x 30 min(-1) per anterior segment at baseline to 19.2+/-4.8 pmol x 30 min(-1) per anterior segment after perfusion with 10(-6) M PGE1 (P < 0.005). Perfusion with 10(-6) M PGF2alpha did not influence baseline cAMP production. Perfusion with 10(-5) M GDP-beta-S, an inhibitor of G protein, before and in combination with 10(-6) M PGE1 completely inhibited the increase in flow and cAMP production as observed after PGE1 alone. Perfusion with 10(-5) M GDP-beta-S alone did not affect baseline cAMP production. CONCLUSIONS: In organ preserved perfused human anterior segments, flow and cAMP production in the perfusate are not mediated by receptor-coupled adenylyl cyclase activity at baseline conditions. Perfusion with PGE1 is suggested to increase flow through the trabecular meshwork by stimulation of prostanoid EP2 receptor subtype, EP4 receptor subtype, or both, coupled to G(s) protein, inducing activation of the adenylyl cyclase catalytic unit. The results may indicate a physiological role for EP2 receptor subtype, EP4 receptor subtype, or both in the modulation of flow through the trabecular meshwork after stimulation.

[Four new drugs for glaucoma: apraclonidine, brimonidine, dorzolamide and latanoprost]. / Vier nieuwe geneesmiddelen bij glaucoom: apraclonidine, brimonidine, dorzolamide en latanoprost.

Glaucoma is in most of cases initially treated with drugs, viz. beta-blocking agents, miotics, sympathicomimetics and carbonic anhydrase inhibitors. The therapy of first choice is a beta-blocking agent, but in approximately 50% of the patients treated the effect becomes inadequate with time and combination therapy is necessary. Recently, four new antiglaucomatous agents have become available: apraclonidine, brimonidine, dorzolamide and latanoprost. Apraclonidine, an alpha 2-adrenergic agonist, is indicated for brief episodes of postlaser rise of the intraocular pressure. Longer treatment may lead to tolerance. Brimonidine, another alpha 2-adrenergic agonist, is indicated for long-term treatment of glaucoma; tolerance does not often occur. Dorzolamide is a local carbonic anhydrase inhibitor which lacks the systemic side effects seen after oral administration of carbonic anhydrase inhibitors. Latanoprost, a prostaglandin F2 alpha-derivative induces an effective decrease of the intraocular pressure if administered as monotherapy and has a good efficacy when combined with other drugs lowering the intraocular pressure. The new antiglaucomatous agents are a welcome addition to the pharmacotherapy, since in many cases they make it possible to postpone or avoid surgery.

Additive ocular hypotensive effect of latanoprost and acetazolamide. A short-term study in patients with elevated intraocular pressure.

OBJECTIVE: To investigate the additive ocular hypotensive effect of latanoprost on the intraocular pressure (IOP) reduction induced by a suboptimal dose of acetazolamide, a carbonic anhydrase inhibitor. DESIGN: A short-term, randomized, placebo-controlled, double-masked study. PARTICIPANTS: Twenty-four patients with glaucoma with elevated IOPs. INTERVENTION: Acetazolamide 250 mg twice daily from day 1 to day 18. Topical 50 micrograms/ml latanoprost or placebo eye drops bilaterally instilled once daily from day 4 to day 18. MEAN OUTCOME MEASURES: IOP, conjunctival hyperemia. RESULTS: The mean IOP of 19.5 mmHg during acetazolamide treatment was further reduced to 16.8 mmHg after topical administration of latanoprost, i.e., a decrease of 2.9 +/- 2.8 mmHg (15%, P < 0.001). Administration of placebo to patients on acetazolamide resulted in an upward drift of 1.3 mmHg (6%, P = 0.03). A modest but statistically significant increase in conjunctival hyperemia was found in the latanoprost-treated group, but did not affect the masking. CONCLUSIONS: This short-term study indicates that the combination of topically applied latanoprost and a suboptimal dose of systemic carbonic anhydrase inhibitor is useful in the management of glaucoma.

Deterioration of visual fields in patients with glaucoma with and without optic disc hemorrhages.

OBJECTIVE: To evaluate visual field deterioration in patients with glaucoma with and without optic disc hemorrhages (DHs). DESIGN: A prospective study at quarterly base involving annual perimetry; mean follow-up of 9 years. SETTING: Outpatient department, nonreferral basis. PATIENTS: Sixty-eight patients with primary open-angle glaucoma, 34 with normal pressure glaucoma (NPG), and 125 with ocular hypertension. RESULTS: Visual field deterioration occurred in 32%, 32%, and 6% of the patients without DHs who had NPG, primary open-angle glaucoma, or ocular hypertension, respectively, while visual field deterioration occurred in 80%, 89%, and 14% of patients with DH, respectively. Cox proportional hazards ratio(CHR) for deterioration in patients with vs patients without DHs was 5.4 for NPG (P<.01) and 3.6 for primary open-angle glaucoma (P<.01). In patients with NPG and DHs, ipsilateral eyes with DHs deteriorated in 58%, while contralateral eyes without DHs deteriorated in 11% (CHR, 8.9; P<.04). For primary open-angle glaucoma and ocular hypertension, progression did not differ between eyes with DHs and contralateral eyes without DHs. Mean (+/-SD) interval between DHs and ipsilateral visual field deterioration was 3.1+/-1.7 years. No difference in the proportion of eyes progressing after single or recurrent DHs was noted. The position of DHs was related to the site of the visual field loss in 44% of the eyes. CONCLUSIONS: The presence of DHs increased the risk of visual field deterioration. Disc hemorrhages were indicative only of deterioration in ipsilateral eyes in patients with NPG.

Fluorescein angiographic evaluation of the effect of latanoprost treatment on blood-retinal barrier integrity: a review of studies conducted on pseudophakic glaucoma patients and on phakic and aphakic monkeys.

Endogenous prostaglandins (PGs) have been claimed to play a role in the development of cystoid macular edema (CME). Two fluorescein angiographic studies evaluating the effect of latanoprost, a new ocular hypotensive PG analogue, on blood-retinal barrier integrity are, therefore, reviewed here. In the first study, six of eight unilaterally aphakic cynomolgus monkeys were treated bilaterally once daily for six months with 0.035% latanoprost (seven times the clinically used oculohypotensive concentration). Two of the animals served as controls. Fluorescein angiography of the fundus after one, three and six months of treatment revealed no leakage of fluorescein in any of the 16 eyes. In another study, pseudophakic eyes of 16 glaucoma patients who received twice-daily treatment with 0.006% latanoprost for four weeks were compared to eight patients treated with placebo. Biomicroscopic examination did not reveal any signs of CME and only one placebo-treated eye revealed a slight perifoveal leakage of fluorescein. These studies suggest that topically-applied latanoprost does not have a fluorescein angiographically detectable direct effect on the integrity of the blood-retinal barrier system in phakic or aphakic monkey eyes or in pseudophakic human eyes. This does not rule out the occurrence of CME in eyes more susceptible to CME, due to vitreous loss, posterior capsulotomy, or other postoperative situations. Especially in those eyes a study with latanoprost is proposed. Since, fluorescein angiography is a rather crude method of detecting abnormalities of the blood-retinal barriers, vitreous fluorometry in addition is suggested.

Reduced intraocular pressure and increased ocular perfusion pressure in normal tension glaucoma: a review of short-term studies with three dose regimens of latanoprost treatment.

Currently used ocular hypotensive agents do not effectively lower intraocular pressure (IOP) in some normal-tension glaucoma (NTG) patients. The prostaglandin F2 alpha analogue, latanoprost, has been shown to reduce IOP in normal subjects and ocular hypertensive glaucoma patients by increasing uveoscleral outflow. This mechanism is expected to be particularly effective in the lower IOP range that is typical of NTG. To date, three dose regimens of latanoprost have been shown to reduce IOP significantly in NTG. The IOP reductions of 14.2% and 15% obtained with twice-daily application of 0.0015% and 0.006% latanoprost, respectively, were comparable to the modest IOP reduction that has been reported for other glaucoma drugs in NTG. In contrast, once-daily application of 0.005% latanoprost resulted in a 21.4% IOP reduction. In another study that included 24-hour monitoring of systemic blood pressure and heart rate in NTG patients, the ocular perfusion pressure was found to improve more on once-daily 0.005% latanoprost than on twice-daily treatment with 0.5% timolol. Thus, once-daily 0.005% latanoprost appears to be a more effective and more convenient ocular hypotensive agent for treating NTG than currently used glaucoma drugs. However, long-term studies will ultimately be needed to establish the efficacy of this new drug to delay or prevent the progression of visual field loss in normal tension glaucoma.

The additive intraocular pressure-lowering effect of latanoprost in combined therapy with other ocular hypotensive agents.

Latanoprost, a prostaglandin F2 alpha analogue prodrug, has been shown to be an effective ocular hypotensive agent when used alone on ocular hypertensive or open angle glaucoma patients. In various studies, the ocular hypotensive effects of latanoprost have also been evaluated when used in addition to, or in combination with, other ocular hypotensive agents. Latanoprost produces an additional reduction of intraocular pressure (IOP) when used in combination with timolol, pilocarpine, acetazolamide and dipivefrin. These represent four different classes of glaucoma drugs-beta-adrenergic antagonists, cholinergic agonists, carbonic anhydrase inhibitors, and adrenergic agonists-all of which reduce the IOP by different mechanisms (reduction of aqueous humor production, increased outflow facility, or by a mixed effect on aqueous humor dynamics). All the available evidence shows that latanoprost produces a clinically significant additive ocular hypotensive effect when used in combination with any currently available ocular hypotensive agent.

Outflow characteristics of isolated anterior segments of human eyes.

PURPOSE: To evaluate the relationship between intraocular pressure (IOP) and flow through the trabecular meshwork in isolated anterior segments of human eyes. Outflow facility (C) is thought to decrease proportionally with increasing IOP in human eyes in vivo and in vitro. METHODS: Twenty-nine eviscerated human anterior segments were perfused with ascending and descending pressure sequences in a stepwise fashion (range, 4 to 40 mm Hg); 11 of the 29 eyes were treated similarly after 20 hours of perfusion at 12 mm Hg. Pressure-flow sequences of individual eyes were evaluated with a linear (constant C) and a nonlinear regression method (C decreasing with increasing IOP). In addition, in eight intact postmortem eyes, pressure-flow characteristics were determined, followed by perfusion of their isolated anterior segments. RESULTS: Pressure-flow sequences as determined by linear regression had an average correlation coefficient of 0.99. Average C (slope of the plot) was 0.26 +/- 0.03 microliter minute-1 mm Hg-1. There was no influence of direction of pressure sequence or time on C. To test for linearity, the hypothetical outflow obstruction coefficient (Q) was determined for each plot. Median Q of 29 eyes was 0.003 mm Hg-1, and in 45% (13 eyes) Q was negative, suggesting facilitation instead of obstruction. This indicates that the outflow obstruction coefficient is not a physiological parameter in isolated anterior segments. CONCLUSIONS: The relationship between IOP and flow through perfused isolated anterior segments of human eyes is linear between 4 and 40 mm Hg, indicating that within this range outflow facility is constant and does not decrease with increasing IOP.

Reduction of intraocular pressure with treatment of latanoprost once daily in patients with normal-pressure glaucoma.

PURPOSE: Currently available ocular hypotensive agents often fail to lower intraocular pressure (IOP) in patients with normal-pressure glaucoma (NPG). The authors evaluated the IOP-reducing potential and side effects of latanoprost, a newly developed ocular hypotensive agent, in this patient group. METHODS: A randomized, double-masked, placebo-controlled cross-over study was performed in 30 patients with NPG, 29 of whom completed the study. During three periods of 3 weeks each, patients received, in a random order, 50 micrograms/ml latanoprost once daily, 15 micrograms/ml latanoprost twice daily, and placebo. Per dose, one drop of the study medication was applied topically in both eyes. At the end of each treatment period, diurnal IOP measurements were obtained. General and ocular symptoms were recorded, and a detailed ocular examination was performed on each visit to monitor side effects. RESULTS: Average IOP reduction after 50 micrograms/ml latanoprost once daily, 15 micrograms/ml latanoprost twice daily, and placebo was 3.6 +/- 1.9 mmHg (21.3%, P < 0.001), 2.4 +/- 1.5 mmHg (14.2%, P < 0.001), and 0.4 +/- 1.8 mmHg (2.4%, not significant), respectively. The difference between the two latanoprost dose regimens was significant (P = 0.001). Efficacy of latanoprost correlated with initial IOP (r2 = 0.76, P < 0.001). A mild, but statistically significant, increase in conjunctival hyperemia was observed in both latanoprost treatment groups. CONCLUSION: Both latanoprost regimens significantly reduce IOP in patients with NPG, but 50 micrograms/ml latanoprost once daily is more effective in reducing IOP than 15 micrograms/ml latanoprost twice daily. Lowering the concentration did not result in an improved side effects profile. Latanoprost is more effective at higher IOP levels.

Evaluation of IBMX-enhanced ocular hypotension after adrenergic agonists in the rabbit eye.

BACKGROUND: 3-Isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, enhanced the reduction of intraocular pressure more after administration of norepinephrine and epinephrine than after isoproterenol. The question arises of whether or not the IBMX-induced enhancement of ocular hypotension is exclusively due to beta 2-adrenoceptor/cAMP stimulation. METHODS: In groups of eight rabbits the ocular hypotensive responses after selective adrenergic agonists were studied in the presence and absence of phosphodiesterase inhibition with IB-MX. RESULTS: Pretreatment with IBMX 1%, applied topically, did not enhance the ocular hypotensive responses after phenylephrine (alpha 1), B-HT920 (alpha 2) and dobutamine (beta 1). The ocular hypotensive responses induced by salbutamol (0.001-0.5%) and higher concentrations of terbutaline were significantly enhanced by IBMX. Combined treatments of terbutaline 0.01% and B-HT920 0.2%, dobutamine 3% and phenylephrine 2%, and dobutamine 3% and B-HT920 0.2% were not associated with enhanced ocular hypotensive responses in the presence of IBMX. The only combination that was associated with a significant enhancement of ocular hypotension when combined with 1% IBMX was phenylephrine 2% and terbutaline 0.01%. A subthreshold dose of phenylephrine 0.1% further increased the enhanced ocular hypotensive responses induced by salbutamol 0.025, 0.2 and 0.5% in combination with IBMX. CONCLUSIONS: Phosphodiesterase inhibition with IB-MX enhances the ocular hypotensive effect induced by catecholamines not only by beta 2-adrenoceptor/cAMP stimulation, but also by simultaneous alpha 1-adrenoceptor stimulation.

Additive effect of latanoprost, a prostaglandin F2 alpha analogue, and timolol in patients with elevated intraocular pressure.

A randomised observer masked clinical study was conducted to assess the additive effect of latanoprost (13,14-dihydro-17-phenyl-18,19,20-trinorprostaglandin F2 alpha-isopropylester) to timolol maleate in patients with elevated intraocular pressure (IOP). Patients were randomly assigned to two treatment groups. One group (n = 10) received timolol, the other group (n = 9) received latanoprost twice daily for 1 week. After 1 week all patients received both timolol and latanoprost. Eyes treated with timolol (mean diurnal IOP (SD) day 0, 24.2 (2.8) mm Hg) and latanoprost (mean diurnal IOP day 0, 28.5 (5.6) mm Hg) showed an IOP reduction of 5.9 (2.3) mm Hg (24%) and 8.9 (2.5) mm Hg (31%), respectively after the first week. Adding latanoprost to the eyes treated with timolol as well as timolol to the eyes receiving latanoprost gave a further reduction of 2.6 (1.1) mm Hg (13%) and 2.6 (2.2) mm Hg (14%), respectively. Only mild transient hyperaemia was observed in patients receiving latanoprost. The results indicate that latanoprost and timolol can be combined successfully and that complete or almost complete additivity is reached even at pressure levels below 20 mm Hg.

Cumulative incidence of patients with disc hemorrhages in glaucoma and the effect of therapy.

PURPOSE: In this longitudinal study, the cumulative incidence of patients with glaucoma and disc hemorrhages was investigated. A possible effect of glaucoma therapy on the incidence rate of disc hemorrhages was evaluated. METHODS: A group consisting of 68 patients with primary open-angle glaucoma (POAG), 34 with normal-pressure glaucoma, and 125 with suspected glaucoma (mean follow-up, 7.3 +/- 2.5 years; range 3-13 years) was observed closely with quarterly examinations. RESULTS: In normal-pressure glaucoma, the cumulative incidence of patients with disc hemorrhages was 35.3%, which was significantly higher than for those with POAG (10.3%; P < 0.01) and for those with suspected glaucoma (10.4%; P < 0.001). The mean follow-up period before a first disc hemorrhage was detected was 2.5 +/- 2.8 years. In the bleeders, recurrent disc hemorrhages were observed in 67% of the patients with normal-pressure glaucoma, 29% of those with POAG, and 54% of glaucoma suspects. In normal-pressure glaucoma, therapy had no effect on the incidence rate of disc hemorrhages. In glaucoma suspects, a significant reduction of the incidence rate of disc hemorrhages per year (0.11 +/- 0.04) was observed during episodes with therapy compared with episodes without (0.43 +/- 0.15; P < 0.05). A concept of two populations (i.e., one with disc hemorrhages and the other never having them) seems to be valid for normal-pressure glaucoma, but not for POAG and suspected glaucoma. CONCLUSION: The cumulative incidence of initial disc hemorrhages increases with time in POAG and suspected glaucoma, but reaches a limit in normal-pressure glaucoma. Glaucoma therapy may reduce the incidence rate of all, initial and recurrent, disc hemorrhages in patients with high pressures, but not in patients with normal-pressure glaucoma.

Adenylyl cyclase in human and bovine trabecular meshwork.

PURPOSE: To determine the basic characteristics and responses of adenylyl cyclase in trabecular tissues. Because the second messenger cyclic adenosine monophosphate can lower intraocular pressure by increasing outflow facility, it is of interest to know which signalling pathways stimulating adenylyl cyclase are involved. METHODS: Adenylyl cyclase activity of bovine and human trabecular meshwork membrane fractions and of whole tissue homogenates (bovine) to forskolin, manganese, fluoroaluminate, isoproterenol, prostaglandins (PGE1, PGE2, PGF2 alpha), and vasoactive intestinal peptide, were evaluated. RESULTS: In bovine trabecular meshwork particulate fractions, adenylyl cyclase was stimulated 3.3- and 2.6-fold over basal by 60 and 2 microM forskolin, respectively, 2.2-fold by fluoroaluminate, and 1.5-fold by PGE1 and PGE2, whereas no or a very week response was obtained with PGF2 alpha, isoproterenol, and vasoactive intestinal peptide. PGE1-induced stimulation was dose-dependent and G-protein-dependent, which provides evidence for EP receptor-mediated activation. Whole tissue homogenates of bovine trabecular meshwork did not differ from the particulate fractions. In human trabecular meshwork membrane fractions adenylyl cyclase stimulation was more pronounced, 12.4- and 5.5-fold by 60 and 2 microM forskolin, respectively, 8.2-fold by fluoroaluminate, and 3-fold by PGE1 and PGE2. PGF2 alpha had no effect. Significant stimulation was obtained with isoproterenol (2.8-fold) and with vasoactive intestinal peptide (1.8-fold). CONCLUSIONS: Human and bovine trabecular meshwork can be stimulated at all known activation levels of adenylyl cyclase. The human adenylyl cyclase system, especially receptor-coupled activity, is more sensitive than that of bovines. Beta-adrenoreceptor stimulation, PGE2, and vasoactive intestinal peptide may have a local physiologic function by activating adenylyl cyclase in human trabecular meshwork.

Platelet aggregation, disc haemorrhage and progressive loss of visual fields in glaucoma. A seven year follow-up study on glaucoma.

Platelet aggregation in vitro, deterioration of visual field defects (VFD) and the prevalence of disc haemorrhages (DH) were assessed in 49 patients with primary open angle glaucoma (POAG) and compared with the findings for 67 individuals with suspected glaucoma (GS) in a seven-year follow-up study (range 5.8 to 8.2 years). The percentage patients with spontaneous platelet aggregation (SPA) was higher for POAG patients with visual field deterioration (60%) than both POAG patients without progressive loss of visual fields (12.5%; P less than 0.005) and those with suspected glaucoma (22.4%; P less than 0.005). The occurrence of DH was higher among POAG patients with progressive loss of visual field (28%) compared to the GS group (8.4%; P less than 0.025) and the group of patients consisting of POAG patients without deterioration of VFD and GS (9.9%; P less than 0.05). DH also occurred more often in patients with low tension glaucoma (41.6%) than in the remaining POAG patients (13.5%; P less than 0.05). No relation between the patients with SPA and the patients with DH was observed.

Effects of cyclic nucleotide analogs on intraocular pressure and trauma-induced inflammation in the rabbit eye.

In this study the effects of cell-permeable 8-bromo-cAMP and 8-bromo-cGMP on intraocular pressure (IOP) and puncture-induced inflammatory response were investigated. Both 8-bromo-cAMP and 8-Bromo-cGMP reduced IOP when given subconjunctivally, but not topically. Subconjunctival administration of 8-bromo-cAMP induced a moderate disruption of the blood-aqueous barrier (BAB); in addition, subconjunctival 8-bromo-cAMP, but not topical 8-bromo-cAMP or subconjunctival 8-bromo-cGMP, reduced the disruption of the BAB and elevation of the aqueous PGE2 level after puncture trauma. It is concluded that the effects of 8-bromo-cAMP depend on the mode of administration, since this determines the concentration of 8-bromo-cAMP reached in the aqueous humor. It is suggested that 8-bromo-cAMP can partially suppress a slight inflammatory response by interference with the release of arachidonic acid from the tissues surrounding the aqueous humor.

Isobutylmethylxanthine enhances adrenergic-induced ocular hypotension in rabbits and beagles.

Isobutylmethylxanthine (IBMX), a phosphodiesterase/adenosine receptor inhibitor, was combined with norepinephrine (nE), epinephrine (Epi) and isoproterenol, respectively, to evaluate their effect on intraocular pressure (IOP). Application of topical IBMX alone had no measurable effect on IOP. When IBMX was combined with nE or Epi the ocular hypotension in rabbits and beagles increased. The Emax for nE alone was 2.9 +/- 0.4 mmHg, for Epi alone 7.3 +/- 0.5 mmHg and for isoproterenol alone 5.1 +/- 0.3 mmHg. The EC50 was 0.2 +/- 0.05% (nE), 0.05 +/- 0.01% (Epi) and 0.003 +/- 0.001% for isoproterenol. When given in combination with 1% IBMX the Emax for nE was 7.4 +/- 1.7 mmHg, for Epi 9.0 +/- 0.8 mmHg and for isoproterenol 6.1 +/- 0.3 mmHg. The corresponding values for EC50 were 0.07 +/- 0.03% (nE), 0.02 +/- 0.006% (Epi) and 0.002 +/- 0.001% for isoproterenol. Combining 1% IBMX with 0.1% Epi increased the aqueous humour cyclic AMP-levels at 1, 3 and 5 hr in rabbits. The results of this study demonstrate that a phosphodiesterase/adenosine receptor inhibitor such as IBMX enhances the reduction in IOP induced by adrenergic agonists.

Increase in ocular blood flow induced by isobutylmethylxanthine and epinephrine.

Alterations in regional blood flow of the eye were studied in rabbits using the radioactively labelled microsphere technique. The animals were topically treated with 1% IBMX, 0.1% epinephrine in combination with 1% isobutylmethyl-xanthine (IBMX), or with 0.1% epinephrine alone. After IBMX there was a tendency towards an increase in blood flow in the iris, ciliary processes and sclera, whereas the choroidal blood flow tended to decrease. After epinephrine the iridial blood flow increased about 50% at 6 hr. After IBMX combined with epinephrine a biphasic response was obtained: an initial decrease in blood flow of the iris, the ciliary processes and to some extent the choroid was followed by a marked and long lasting increase in blood flow from 2.5 to 7.5 hr in the iris (up to 220%), ciliary processes (123%) and sclera (115%). The choroidal blood flow was not increased. The marked increase in blood flow of the iris and the ciliary processes indicates that the reduction of intraocular pressure seen after topical treatment with a combination of epinephrine and IBMX, is not based on a vascular mechanism. The increase of ocular blood flow after a combination of IBMX and epinephrine is probably based on increased cAMP secondary to inhibition of phosphodiesterases. This may indicate the presence of beta-adrenergic receptors in the ocular vasculature.