Indirect sympatholytic actions at β-adrenoceptors account for the ocular hypotensive actions of cannabinoid receptor agonists

Intraocular pressure (IOP) is the primary risk factor for glaucoma, a blinding eye disease. Cannabinoid agonists have long been known to decrease IOP, suggesting they may be useful in glaucoma treatment. However, the specific mechanism by which cannabinoids generate this ocular hypotensive effect remains unknown. The current evidence suggests the cannabinoids reduce IOP through actions at cannabinoid 1 (CB(1)) receptors within the eye, and adrenergic receptors (ARs) may also contribute to this action of cannabinoids. Considering this, the present study aimed to elucidate the mechanism behind the ocular hypotensive properties of cannabinoids through the use of mice genetically lacking either cannabinoid receptors or βARs. Cannabinoid agonists, βAR antagonists, and βAR agonists decreased IOP in wild-type mice and CB(2)(-/-) mice. In contrast, none of these compounds were found to reduce IOP in βAR(-/-) or CB(1)(-/-) mice. Desensitization of the βARs and depletion of catecholamines in wild-type mice also eliminated the ability of the cannabinoid agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55,212-2) to reduce IOP, strongly implicating a role for both βARs and catecholamines in the ocular hypotensive properties of cannabinoids. Finally, CB(1) receptors were shown to colocalize with tyrosine hydroxylase, a marker for adrenergic neurons. Taken together, these findings suggest that βARs are required for the ocular hypotensive properties of cannabinoids, and cannabinoids reduce IOP by acting as indirect sympatholytics and inhibiting norepinephrine release within the eye.

Fadolmidine-induced ocular hypotension in normotensive rabbits

Fadolmidine, a novel selective α-adrenoceptor agonist, was evaluated for its efficacy to lower intraocular pressure in normotensive rabbits (n = 5–6). The dose-response profile between 0.004 μg and 12.5 μg of fadolmidine was determined. The effect of pH on the partition of fadolmidine was studied in order to select an optimal pH for topical fadolmidine administration. After topical administration, fadolmidine significantly lowered the intraocular pressure in normotensive rabbits. The onset of action was immediate, with no initial increase in intraocular pressure. A significant decrease in intraocular pressure was already observed at 1 h after dosing. The maximum decrease in intraocular pressure was observed after a 2.5 μg dose of fadolmidine in both eyes at 2 h after dosing. The mean maximum decrease in the treated and untreated eye was 6.4 mmHg and 3.9 mmHg, respectively. In conclusion, fadolmidine is a potent intraocular pressure lowering agent. In addition, fadolmidine does not cause a significant initial increase in intraocular pressure. Because of the strong dependence of the distribution coefficient on pH, the pH of the administered solution is important, with physiological pH being optimal in this respect.

Stereoselectivity of satropane, a novel tropane analog, on iris muscarinic receptor activation and intraocular hypotension

AIM

To study the stereoselectivity of satropane (3-paramethylbenzene sulfonyloxy-6-acetoxy tropane), a novel tropane analog, on iris muscarinic receptor activation and intraocular hypotension.

METHODS

The assays for radioligand-receptor binding, the contractile responses of isolated iris muscle, the miosis response, and the intraocular hypotension of the enantiomers of satropane were investigated.

RESULTS

In the binding analysis, S(-)satropane (lesatropane) completely competed against the [3H]quinuclydinyl benzilate-labeled ligand at muscarinic receptors in the iris muscle, whereas R(+)satropane failed to completely compete. In an isolated iris contractile assay, R,S(+/-)satropane and S(-)satropane produced a concentration-dependent contractile response with similar efficacy and potency to that of carbachol. R(+)satropane did not induce any contractile response. In the pupil diameter measurement assay in vivo, S(-)satropane induced miosis much more effectively than pilocarpine, while R(+)satropane failed to produce any miosis. In the water loading-induced and methylcellulose-induced ocular hypertensive models, S(-)satropane, but not R(+)satropane, significantly suppressed intraocular pressure at a much lower concentration than pilocarpine.

CONCLUSION

The agonistic and hypotensive properties of satropane on rabbit eyes are stereoselective, with the S(-)isomer being its active form.

[Late postoperative choroidal detachment]

Three eyes of three patients with advanced primary open angle glaucoma developed hypotony and choroidal detachment 2-3 months following technically uncomplicated trabeculectomy, in one patient and facoemulsification in two patients. The two latter patients had undergone trabeculectomy previously. No wound or bleb leakage were found. Patients did not receive any antiglaucoma medications before the detachment. After treatment with topical corticosteroids and cycloplegic eyedrops both patients showed marked clinical improvement within 2-6 weeks. However, one of the patients after phacoemulsification developed recurrent choroidal detachment shortly after application of timolol drops used due to IOP elevation. Detachment resolved spontaneously after discontinuation of timolol.

Hypotony and choroidal detachment as a complication of topical combined timolol and dorzolamide

PURPOSE

Hypotony with choroidal detachment is a rare complication of glaucoma medication. In this study, we report on a case which supports the hypothesis that has been proposed to explain this phenomenon.

DESIGN

This study was designed as an observational case report.

CASE REPORT

A woman with chronic glaucoma underwent trabeculectomy on both eyes. Low intraocular pressure (IOP) developed in 1 eye only, with no visual change for many years. After cataract surgery, the IOP increased, necessitating treatment with topical timolol 0.5% and dorzolamide 2%. She developed monocular hypotony and choroidal detachment 3 months later. This complication occurred in the eye that had previously had a low IOP and resolved completely when topical medication was stopped. The choroidal detachment recurred when rechallenged with the same medication.

CONCLUSIONS

Topical aqueous suppression therapy can result in hypotony and choroidal detachment in an eye in which relatively low IOP has been maintained for many years after glaucoma filtration surgery. The problem resolves on stopping the medication.

Morphine-Induced Reduction of Intraocular Pressure and Pupil Diameter: Role of Nitric Oxide

The present study was performed to evaluate the role of nitric oxide in the intraocular pressure (IOP) lowering effect and in the miotic action of morphine. The IOP was measured in conscious, normal, dark-adapted New Zealand white rabbits using a calibrated pneumatonometer. Experiments were conducted, in which rabbits' eyes were treated with morphine topically and unilaterally, while the fellow eyes received vehicle. IOP and pupil diameter (PD) measurements were taken 0.5 and 0 h before morphine administration and 0.5, 1, 2, 3, 4, and 5 h thereafter. The effects of a nonselective opioid receptor antagonist (naloxone), a nitric oxide synthase inhibitor (Nomega-nitro-L-arginine methyl ester; L-NAME), and a sulfhydryl reagent (reduced L-glutathione; GSH) on morphine-mediated changes in IOP and PD were also determined. Morphine (10, 33, and 100 microg) produced concentration-dependent decreases in IOP and reduced PD in both treated and untreated eyes of New Zealand white rabbits. IOP-lowering effect of morphine (100 microg) and reduction in PD were both significantly inhibited by pretreatment with naloxone (100 microg), L-NAME (0.5%), or GSH (100 microg). The results from this study indicate that morphine-induced ocular hypotension and reduction in PD are opioid-receptor-mediated responses that are associated with the release of nitric oxide. Because the mu3 opioid receptor subtype has a nitric-oxide-releasing activity and is sensitive to inactivation by GSH, it is concluded that morphine-induced ocular hypotension and miosis are mediated, in part, by activation of mu3 opioid receptors.

Noninvasive intraocular pressure measurements in mice by pneumotonometry

PURPOSE

To develop a reliable, noninvasive, continuous, and easily implemented system for measuring intraocular pressure (IOP) in mice.

METHODS

Pneumotonometry was adapted for measurement of mouse IOP. Measurements were compared with those obtained with the servo-null micropipette system (SNMS) and with direct anterior chamber cannulation. Heart rate was monitored by the precordial pulse, EKG, or tail pulse in anesthetized mice. The characteristic ocular hypotensive response to mannitol was assessed as an additional validation of the

METHOD

RESULTS

Measurements of IOP obtained using pneumotonometry agreed closely with values measured by SNMS or by direct cannulation. IOP oscillations were synchronous with the heart rate, with a coherence peak between them of approximately 2 Hz, equal to the pulse frequency. Hypertonic mannitol reduced IOP from 13.7 +/- 0.9 mm Hg by 7.7 +/- 0.7 mm Hg after 15 minutes.

CONCLUSIONS

Pneumotonometry is a reliable and noninvasive method for the measurement of IOP in mice and may permit comparisons of IOP to hemodynamic factors. This system is simpler and more adaptable for glaucoma research than previously reported methodologies for measuring IOP in mice.

Ocular pharmacology of bicyclic hexahydroaporphines

This paper explores the ocular hypotensive actions of bicyclic analogs of hexahydroaporphine (HHA), specifically nor-HHA, in an attempt to shed light on the mechanism(s) by which they lower intraocular pressure (IOP). Studies involving the measurement of IOP and aqueous humor production were conducted in ocular normotensive albino rabbits, while those involving smooth muscle contractility utilized isolated bovine iris. The ability of nor-HHA to produce a sustained drop in IOP is linked to both a functioning adrenergic nervous system and the availability of the products of cyclooxygenase metabolism. Although aqueous flow is not impacted by the bicyclic structures, the significant enhancement of outflow facility points to a probable mechanism of IOP-lowering action. Nor-HHA had no direct contractile or relaxant action on bovine irides, but does cause a concentration-dependent inhibition of carbachol-evoked contractions. This inhibition was reversed by inhibitors of phospholipase A(2) and cyclooxygenase, but not by inhibitors of lipoxygenase, again indicating a role for prostaglandins in the ocular pharmacological action of bicyclic HHAs. Pretreatment with a nitric oxide (NO) scavenger also reversed the ability of nor-HHA to inhibit carbachol-induced contractions, implying a role for NO in the postjunctional actions of HHAs.

PD128,907 induces ocular hypotension in rabbits: involvement of D2/D3 dopamine receptors and brain natriuretic peptide

The purpose of this study was to determine the potential role of brain natriuretic peptide (BNP) in the PD128,907 (a dopamine D2/D3 receptor agonist)-induced ocular hypotension in rabbits. The effects of topical application of PD128,907 (75, 250, 750 microg) on intraocular pressure (IOP) were investigated. The lowest dose (75 microg) did not alter IOP; while the higher doses (250 and 750 microg) reduced IOP bilaterally. The PD128,907 (250 microg)-induced ocular hypotension, which lasted 3 hours, could be blocked by raclopride (1000 microg), a dopamine D2/D3 receptor antagonist, as well as by sympathetic denervation. Aqueous humor inflow was reduced by intravitreal injection of PD128,907 (10 microg) by 67% at 1 and 2 hours, which then returned to baseline at 3 hours. Furthermore, topical application of PD128,907 (250 microg) elevated aqueous BNP levels by 3-fold at 30 minutes, 6-fold at 1 hour and 5-fold at 2 hours, which could be blocked by pretreatment with raclopride (250 microg). Taken together, PD128,907-induced ocular hypotension by activation of dopamine D2/D3 receptors. This action was associated with reduced aqueous humor inflow and increased aqueous BNP levels.

The Comparative Cardiovascular, Pulmonary, Ocular Blood Flow, and Ocular Hypotensive Effects of Topical Travoprost, Bimatoprost, Brimonidine, and Betaxolol

OBJECTIVE

This study evaluated systemic and ocular acute safety and intraocular pressure (IOP)-lowering efficacy of travoprost 0.004% and bimatoprost 0.03%, compared to brimonidine 0.2% and betaxolol 0.25% in healthy subjects.

PATIENTS AND METHOD

Nineteen (19) young men, ages between 24 and 42, were enrolled in a single-center, institutional randomized, double-masked, crossover clinical trial. Baseline IOP, heart rate, blood pressure, and respiratory rate were recorded at hour 0. At minute 30, heart rate, blood pressure, respiratory rate, and spirometry were measured. At hour 1, color Doppler imaging of retrobulbar vessels was performed. At hour 2, heart rate, blood pressure, and respiratory rate were measured; spirometry and a 15-minute treadmill test were performed. The same protocol was applied after one drop of a study medication was instilled into each eye on four subsequent visits at 5-day intervals.

RESULTS

Travoprost and bimatoprost did not cause significant reductions in systolic blood pressure during exercise and recovery. The mean respiratory rate and forced expiratory volume in 1 second were not significantly altered by any study medication. Travoprost reduced the resistive index and increased blood velocities in the ophthalmic artery and its branches. Bimatoprost caused a significant increase in end diastolic velocity of the ophthalmic artery. At hour 6, all medications reduced IOP significantly (p < 0.05). The most frequent ocular side effect of travoprost and bimatoprost was conjunctival hyperemia.

CONCLUSION

Travoprost and bimatoprost were found to be systemically safe and caused an increase in blood-flow velocities of the retrobulbar vessels after a single-dose application. Their ocular hypotensive effect was comparable to that of brimonidine and greater than that of betaxolol in healthy subjects.

Hypotony and choroidal effusion induced by topical timolol and dorzolamide in patients with previous glaucoma drainage device implantation

Three patients with glaucoma drainage devices and one patient who had trabeculectomy with mitomycin C were treated with a combination of topical timolol 0.5% and dorzolamide hydrochloride in the late postoperative period to decrease the intraocular pressure to the target level. All four patients developed ciliochoroidal effusions with hypotony that resolved with the discontinuation of the topical medication. Aqueous suppressants can induce ciliochoroidal effusions and hypotony in the late postoperative phase in some patients with glaucoma drainage devices. Discontinuation of the medication usually results in the resolution of the choroidal effusions.

[Bilateral uveitis with definitive hypotony caused by systemic cidofovir]

We report the case of a 52-year-old man with AIDS and CMV bilateral retinitis, treated first with ganciclovir (cymevan) and then with cidofovir. During the treatment, the patient complained of a sharp decrease in visual acuity. Cycloplegics and topical corticosteroids were given. Then cidofovir was stopped and replaced with intravenous Foscavir because of the clinical inefficacy. The anterior uveitis resolved but the ciliary secretion has not stopped after 12 months of follow-up. The patient presented +11 hypermetropia with a choroidal edema and bilateral cataract. This case is interesting for its permanent hypotony and bilateral uveitis. A literature search has brought out a rate of only 3% of chronic hypotony. We hypothesize bilateral iatrogenic ciliary body necrosis, as described in the animal models.

[Ocular complications of the virostatic drug cidofovir]

Cidofovir, a nucleotide analogue virostatic drug is effective in the treatment of herpes virus infections. However, cytomegaly infection is the prime indication due to its adverse effects. There is growing evidence suggesting cidofovir's effectiveness against progressive multifocal leukoencephalopathy (PML) caused by a reactivation of JC-virus. Chronic ocular hypotension which seems to be therapy refractory and anterior uveitis are considered to be the most serious ocular complications of cidofovir. Secondary side effects such as macular folds, retinal or choroidal detachment can result in a permanent loss of vision. Little is known about the pathology of reduced intraocular pressure and only few reports deal with therapeutical attempts to compensate this complication. Abandoning cidofovir presently remains the only therapeutic option. To avoid serious damage it is of utmost importance to monitor all patients undergoing cidofovir administration for signs of anterior uveitis and ocular hypotension.

Ocular hypotensive effects of melatonin receptor agonists in the rabbit: further evidence for an MT3 receptor

(1) Melatonin is involved in the control of intraocular pressure during the night and day photoperiod. We have investigated the receptor that regulates intraocular pressure in New Zealand white rabbits by means of agonists and antagonists of melatonin receptors. (2) Melatonin and its analogues: 2-Phe-melatonin, 6-Cl-melatonin, 2-I-melatonin, 5- methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT) and N-acetyltryptamine all produced a reduction in intraocular pressure. Dose-response analysis for these compounds gave pD(2) values of 9.3+/-0.24 for melatonin; 9.0+/-0.09 for 6-Cl-melatonin; 9.0+/-0.84 for 2-I-melatonin; 8.9+/-0.07 for 5-MCA-NAT; 8.7+/-0.18 for 2-Phe-melatonin and 9.4+/-0.30 for N-acetyltryptamine (all n=8). (3) At a dose of 0.5 nmol (in 10 micro l) melatonin and the selective melatonin MT(3) agonist 5-MCA-NAT, induced greater reductions of intraocular pressure (22.8+/-2.3% and 32.5+/-1.4%, respectively) than the other compounds. (4) The melatonin-receptor antagonists, prazosin, DH-97 and 4-P-PDOT, reversed the effect of 5-MCA-NAT in a dose-dependent manner, with pA(2) values of 13.5+/-0.17 for prazosin, 10.6+/-0.16 for DH-97 and 9.4+/-0.20 for 4-P-PDOT (n=8). (5) Cholinoceptor antagonists (hexamethonium and atropine) and alpha(2)- and beta(2)-adrenoceptor antagonists (yohimbine and ICI 118,551) partially reversed the effects produced by melatonin and 5-MCA-NAT, suggesting the possible involvement of cholinergic and noradrenergic systems in the hypotensive actions mediated by melatonin agonists. The alpha(1)-adrenoceptor antagonist, corynanthine, had no significant effect. (6) The strong hypotensive effect of the MT(3) agonist, 5-MCA-NAT, suggests that this compound may be a useful agent for treating those pathologies where intraocular pressure is abnormally elevated.

Ocular hypotensive action of topical flunarizine in the rabbit: role of sigma 1 recognition sites

In a previous study we ascertained the presence of sigma1 and sigma2 recognition sites in the rabbit iris-ciliary body, an ocular structure involved in aqueous humor production and drainage. We characterized the sigma1 sites using the preferential ligand (+)-pentazocine, which caused a significant reduction of intraocular pressure (IOP). In the present study, flunarizine, a calcium channel blocker with a complex pharmacological profile, bound to sigma1 sites expressed in the iris-ciliary body with moderate affinity (K(i) = 68 nM). Unilateral topical flunarizine (0.01-0.1%) caused a dose-related reduction of IOP in ocular normotensive rabbits and in the alpha-chymotrypsin model of ocular hypertension, without altering the IOP of the contralateral eye. This activity was blocked by the sigma1 site antagonist NE-100 [N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine HCl] which, by itself, had no effect on IOP. Detection of flunarizine in rabbit iris-ciliary body homogenates, after topical instillation, showed that it adequately penetrates the rabbit eye. To investigate mechanisms that may contribute to ocular hypotension induced by sigma1 agonists, we carried out in vitro studies on the isolated rabbit iris-ciliary body. Flunarizine (IC50 = 5. 96 nM) and (+)-pentazocine (IC50 = 3. 81 nM) inhibited [3H]norepinephrine release. Moreover, flunarizine (IC50 = 6.34 nM) and (+)-pentazocine (IC50 = 27.26 nM) also antagonized isoproterenol-induced cAMP accumulation. The action of flunarizine and (+)-pentazocine was sensitive to NE-100 antagonism; however, this latter compound partially prevented their effect on [3H]norepinephrine and cAMP accumulation. These findings indicate that flunarizine and (+)-pentazocine interact with ocular sigma1 sites and may prove effective in the control of ocular hypertension.

Treatment of severe ocular hypotony in AIDS patients with cytomegalovirus retinitis and cidofovir-associated uveitis

OBJECTIVE

To describe the medical treatment of severe ocular hypotony in HIV-seropositive patients with cytomegalovirus retinitis and cidofovir-associated uveitis.

PATIENTS AND METHODS

Two HIV-seropositive patients with cytomegalovirus retinitis and cidofovir-associated uveitis complicated by severe ocular hypotony were unresponsive to conventional therapy after treatment with cidofovir was stopped. They were subsequently treated successfully with ibopamine 2% eyedrops and dexamethasone 0.1% eyedrops.

RESULTS

In both cases, an increase in intraocular pressure to normal values was observed on average 18.5 days after starting treatment. Intraocular pressure remained stable while on therapy for a mean follow-up of 9.5 months. During the follow-up period, any attempt to stop treatment was followed by an intraocular pressure decrease; conversely, restoration of therapy increased intraocular pressure to normal values. No reactivation of cidofovir-associated uveitis or cytomegalovirus retinitis was observed during the follow-up period.

CONCLUSIONS

Ibopamine 2% eyedrops in combination with dexamethasone 0.1% eyedrops is a satisfactory therapy for severe ocular hypotony in patients with cytomegalovirus retinitis and cidofovir-associated uveitis.

Intraocular pressure responses to the adenosine agonist cyclohexyladenosine: evidence for a dual mechanism of action

PURPOSE

Previous studies have shown that adenosine agonists are effective in reducing intraocular pressure (IOP). However, the mechanism(s) responsible for this ocular hypotensive effect has not been established. This study evaluates the relative contribution of changes in aqueous flow and outflow facility associated with the ocular hypotensive response to the adenosine agonist cyclohexyladenosine (CHA).

METHODS

New Zealand White rabbits were treated topically in one eye with the adenosine A(1) agonist CHA. Changes in IOP, aqueous flow, and total outflow facility at various times after CHA administration were then determined.

RESULTS

These studies demonstrated that CHA produces a dose-related reduction in IOP. Analysis of the dose-response curve revealed an ED(50) and a Hill coefficient of 87 microg and 1.9, respectively. Aqueous flow measurements demonstrated that 1.5 hours after CHA administration, aqueous flow was reduced by 35%. However, by 3.5 hours postdrug, no significant change in aqueous flow was observed. Measurement of the outflow facility found no significant change in facility 1.5 hours after CHA administration. However, by 3.5 hours after CHA administration, outflow facility was significantly increased by 85%.

CONCLUSIONS

These data demonstrate that the adenosine agonist CHA lowers IOP in a dose-related fashion. This hypotensive action results from an early reduction in aqueous flow followed by a subsequent increase in outflow facility. This dual mechanism of action is consistent with analysis of CHA dose-response curve, which indicates that the reduction in IOP induced this agonist's results from multiple mechanisms of action.

[Ocular complications after treatment with intravenous cidofovir for cytomegalovirus retinitis]

PURPOSE

To describe the ocular changes observed in six patients treated with intravenous cidofovir for cytomegalovirus retinitis.

METHODS

We have studied six patients (12 eyes) treated with intravenous cidofovir. A complete ophthalmologic examination was performed before and after each dose during the follow-up period, paying special attention to intraocular pressure changes.

RESULTS

Three cases of non-granulomatous anterior uveitis with good response to conventional treatment were detected. The intraocular pressure decreased after the administration of the two first doses of the drug (p<0.01), and was followed by stabilization of the intraocular pressure with the next doses. In two of the eyes (16.7%), the decrease in the intraocular pressure was more than 50% in comparison to the measurements at the onset of treatment. In three eyes (18.7%), we detected acute anterior uveitis, which responded well to conventional treatment.

CONCLUSIONS

The intravenous administration of cidofovir for the treatment of cytomegalovirus retinitis is associated with important ocular changes that must be carefully observed in the follow-up of these patients.

Enhanced ocular hypotensive response to timolol in rabbits with prior dexamethasone treatment

The purpose of this study was to determine glucocorticoid modulation of ocular pressure to timolol applied topically to rabbit eyes that were pretreated with dexamethasone. Rabbits were pretreated with five applications of topical 0.007% of dexamethasone (0.01% dexamethasone phosphate) or saline drops, administered at ten min intervals. The eyes were then treated with timolol maleate drops at concentrations of free base of 0.00007%, 0.0007%, 0.007% and 0.07%. An additional group of rabbits received dexamethasone pre-treatment only. Intraocular pressure was measured for the next four hr. Enhanced lowering of intraocular pressure was observed with dexamethasone pretreatment. Rabbits receiving the smaller dose of timolol had the least decrease in pressure. The most significant decreases in pressures occurred at 45 min after the administration of timolol with an average difference of 4.8 mm Hg between the timolol- and dexamethasone/timolol-treated eyes for the three largest concentrations of timolol. This synergism between glucocorticoids and beta-adrenergic blockers in lowering IOP may be potentially useful in the therapy of ocular hypertension and glaucoma.

Ocular side-effects from systemic HPMPC (Cidofovir) for a non-ocular cytomegalovirus infection

PURPOSE

To report a case of anterior uveitis and ocular hypotony during HPMPC treatment of a cytomegalovirus infection without ophthalmic involvement.

METHODS

A 61-year-old bisexual white man with AIDS presented with moderate anterior uveitis and ocular hypotony after 8 weeks of intravenous HPMPC and oral probenecid co-treatment of a presumed recurrence of cytomegalovirus encephalitis.

RESULTS

There was no evidence of an ocular cytomegalovirus infection. Cidofovir-related uveitis was diagnosed, and the HPMPC-probenecid co-treatment was switched to ganciclovir monotherapy. The ocular inflammation was successfully managed with topical steroids and mydriatics.

CONCLUSIONS

This description of ophthalmic side effects from systemic HPMPC in the absence of ocular cytomegalovirus infection supports the hypothesis that anterior uveitis and ocular hypotony result from a direct interaction between the drug and the ciliary body.

Isolation of a muscarinic alkaloid with ocular hypotensive action from Trophis racemosa

A muscarinic alkaloid with a quaternary nitrogen was isolated from Trophis racemosa. Aqueous solutions (0.5%-2%) of the chloride salt of the alkaloid produced dose-dependent reductions of intra-ocular pressure ranging from 6.6 +/- 0.7 mmHg to 15.7 +/- 0.3 mmHg, (p < 0. 001, n = 5) in dogs. Atropine (0.1 mL of a 1% solution) and pirenzepine at a non selective antagonist dose (0.1 mL of 0.5% solution) for M(1) and M(3) receptors blocked the reduction of intra-ocular pressure, but alpha-adrenoceptor blockade with phenoxybenzamine (0.1 mL of a 1% solution) did not block the reduction of intra-ocular pressure. On the isolated guinea-pig ileum and trachea, the alkaloid produced contractions which were inhibited by atropine (6 x 10(-7) M or 0.4 microg/mL) and by pirenzepine at a non-selective antagonist dose (3.1 x 10(-6) M or 1.3 microg/mL) for M(1) and M(3) receptors. But neither selective blockade of M(2) receptors with gallamine (1.7 x 10(-6) M or 1.5 microg/mL) nor selective blockade of M(1) receptors with pirenzepine (7 x 10(-9) M or 3 ng/mL) inhibited the alkaloid-induced contractions. There was also no inhibition of the alkaloid-induced contractions in the presence of ganglionic nicotinic receptor blockade with pentolinium (5.6 x 10(-7) M or 0.3 microg/mL) and hexamethonium (1.7 x 10(-6) M or 0.6 microg/mL), but nicotine-induced contractions were inhibited by these ganglionic blockers. These results suggest that a muscarinic alkaloid from Trophis racemosa produced ocular hypotension via M(3) receptor stimulation in dogs.

Intraocular pressure changes in the vitreon study

BACKGROUND AND OBJECTIVE

To detect the effect of Perfluoroperhydrophenanthrene (vitreon) on intraocular pressure (IOP) changes.

PATIENTS AND METHODS

One hundred-five eyes with proliferative vitreoretinopathy undergoing vitrectomy using vitreon as an intraoperative surgical adjunct were randomized to 2 groups. Vitreon was completely removed in 43 eyes (Group A) at the end of operation while it was left intravitreally in 62 eyes (Group B) for 4 weeks. Patients were followed for at least 18 months.

RESULTS

During the first postoperative week, 6 eyes (14%) in Group A and 14 eyes (22%) in Group B had IOP of 23 mm Hg or more (P = .393) while no eyes in either group had hypotony. At the last follow-up 2 eyes (5%) in Group A and 6 eyes (10%) in Group B showed chronic hypotony (P = .561).

CONCLUSION

Although postoperative chronic hypotony risk increased twofold by vitreon when it was left intravitreally for 4 weeks, this difference was statistically insignificant. Vitreon can be used as a vitreous substitute for 4 weeks in this regard.

Ocular complications of intravenous cidofovir for cytomegalovirus retinitis in patients with AIDS

PURPOSE

To describe the frequency of anterior uveitis and ocular hypotony in cidofovir-treated patients with acquired immune deficiency syndrome (AIDS)-related cytomegalovirus (CMV) retinitis.

METHODS

A retrospective review was performed of all patients with AIDS-related CMV retinitis during a 12-month period. The CMV retinitis activity, concurrent illnesses and medications, and CD4+ lymphocyte count were recorded in addition to the degree of anterior chamber inflammation and intraocular pressure at each visit. The frequency of uveitis and ocular hypotony in cidofovir-treated patients was determined and the possible influence of other ocular and systemic factors considered.

RESULTS

Eight of 9 patients on cidofovir developed anterior uveitis. The cellular anterior chamber activity resolved with topical corticosteroid administration in all eyes with uveitis but significant flare persisted despite topical steroids in 3 patients. Posterior synechiae responded poorly to topical mydriatic therapy, resulting in inadequate mydriasis which significantly limited the fundal view. One patient developed a visually significant unilateral hypotonous maculopathy.

CONCLUSIONS

Patients treated with intravenous cidofovir for AIDS-related CMV retinitis are at significant risk of ocular adverse effects. Prompt treatment with topical corticosteroids and mydriatics may control uveitis and in some cases cidofovir treatment may be cautiously continued. In the event of ocular hypotony cidofovir should be discontinued in favour of an alternative anti-cytomegaloviral agent.

Elevated intraocular pressure and hypotony following silicone oil retinal tamponade for complex retinal detachment: incidence and risk factors

OBJECTIVE

To evaluate the incidence of and risk factors for persistently elevated intraocular pressure (IOP) and hypotony in patients who have undergone pars plana vitrectomy with silicone oil injection for the management of complex retinal detachment.

SUBJECTS AND METHODS

The medical records of 532 patients who underwent silicone oil injection for the management of complex retinal detachments between January 1, 1991, and December 31, 1996, at the Bascom Palmer Eye Institute, Miami, Fla, were reviewed. Elevated IOP was defined as elevated IOP requiring an operation at any time postoperatively or a persistently elevated IOP of greater than 25 mm Hg at or after the 6-month visit. Hypotony was defined as a persistent IOP of 5 mm Hg or less at or after the 6-month visit. Patients with transient perioperative IOP fluctuations were not counted.

RESULTS

Survival analysis for patients without cytomegalovirus retinitis (n = 383) revealed that 12.9% had an elevated IOP and 14.1% had hypotony by 6 months, 21% had an elevated IOP and 20.3% had hypotony by 1 year, and 29.5% had an elevated IOP and 27.3% had hypotony by 2 years. Among patients with cytomegalovirus retinitis (n = 149), none had a persistently elevated IOP, 10% had hypotony by 6 months, and 5.9% had persistently elevated IOP and 10% developed chronic hypotony by 1 year. A history of glaucoma before silicone oil retinal tamponade (P = .03), diabetes mellitus (P = .02), and a high IOP on the first postoperative day (P = .006) were risk factors for elevated postoperative IOP in patients without cytomegalovirus retinitis. Risk factors for postoperative hypotony in patients without cytomegalovirus retinitis included preoperative hypotony (P<.001) and aphakia (P = .03).

CONCLUSIONS

An elevated or low IOP often develops postoperatively in patients without cytomegalovirus retinitis who undergo silicone oil injection for the management of complex retinal detachment. Risk factors for an elevated postoperative IOP include a history of glaucoma, diabetes mellitus, and a high IOP on the first postoperative day. Risk factors for hypotony include preoperative hypotony and aphakia.

Effect of the CB1 receptor antagonist, SR141716A, on cannabinoid-induced ocular hypotension in normotensive rabbits

The present study attempts to indirectly determine if a neuronal cannabinoid (CB1) receptor mediates the intraocular pressure (IOP) reduction effects of arachidonoyl ethanolamide (AEA), its R-alpha-isopropyl analog, and the non-classical cannabinoid, CP-55,940. A series of these cannabinoids were dissolved in an aqueous 10-20% 2-hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD) solution (containing 3% polyvinyl alcohol) and administered (25-62.5 microg) unilaterally to normotensive rabbit eyes. This was repeated on animals pre-treated with a subcutaneous injection (2.5 mg/kg) of the highly specific CB1 receptor antagonist, SR 141716A, dissolved in an aqueous 42% 2-HP-beta-CD solution. AEA, its R-alpha-isopropyl analog, and CP-55,940 reduced IOP upon topical application to a greater degree than was detected in the untreated eye. This reduction was eliminated for the latter two compounds by subcutaneous (s.c.) pretreatment of the rabbits with the CB1 receptor antagonist, but the IOP properties of AEA remained unchanged. SR 141716A administered alone (s.c.), elevated the IOP of both eyes. A CB1 receptor seems involved in the IOP reduction induced by either R-alpha-isopropyl anandamide or CP-55,940. However, AEA apparently functions through a different mechanism.

Outcomes of primary phakic trabeculectomies without versus with 0.5- to 1-minute versus 3- to 5-minute mitomycin C

PURPOSE

To compare the intraocular pressure and hypotony outcomes of primary phakic trabeculectomies with no mitomycin C (MMC), shorter MMC, and longer MMC exposure.

METHODS

We evaluated primary phakic trabeculectomies with no MMC (36 eyes of 36 patients), 0.5- to 1-minute MMC (50 eyes of 50 patients), and 3- to 5-minute MMC (38 eyes of 38 patients) at the concentration of 0.5 mg/ml. Successful trabeculectomy was defined as an intraocular pressure of 21 mm Hg or less without development of a marked visual acuity loss associated with prolonged hypotony (intraocular pressure < 6 mm Hg over 3 months) and without the need for additional surgery to control intraocular pressure or treat postoperative complications.

RESULTS

The three groups were similar in demographics, preoperative intraocular pressure, and medical dependency. However, the incidence of hypotony during the postoperative periods of 3 to 12 months was significantly higher in the 3- to 5-minute MMC group (P < .05, chi-square test). Severe visual acuity loss associated with hypotony was also more frequently found in the 3- to 5-minute MMC group than in the 0.5- to 1-minute (P = .009, chi-square test) group or the control group (P = .014, chi-square test). In addition, the success probabilities were significantly different among the three groups (P = .001, Kaplan-Meier survival analysis with log-rank test) and were the highest in the 0.5- to 1-minute MMC group and the lowest in the 3- to 5-minute MMC group.

CONCLUSION

Shorter application (0.5 to 1 minute) of MMC appears to be optimal for the successful outcome of primary phakic trabeculectomy compared with no MMC or longer application of MMC at a concentration of 0.5 mg/ml.

Lisuride acts at multiple sites to induce ocular hypotension and mydriasis

Topically unilaterally applied lisuride caused dose-related lowering of intraocular pressure in ipsilateral (treated) but not in contralateral eyes of normal rabbits. The ocular hypotensive response induced by lisuride was antagonized by pretreatment with metoclopramide, a dopamine receptor antagonist, and was partially reduced by local sympathetic denervation. In contrast to the unilateral effect on intraocular pressure, lisuride caused mydriasis in both eyes. Mydriasis was of greater magnitude and more sustained in normal eyes compared to sympathetically denervated eyes. Additional in vivo experiments demonstrated that lisuride caused dose-related suppression of neuronally initiated contractions of cat nictitating membrane. In in vitro experiments lisuride caused dose-related inhibition of norepinephrine release from isolated rabbit iris-ciliary bodies. Pretreatment with Bay K 8644, a calcium channel activator, did not attenuate lisuride-induced inhibition of norepinephrine release in isolated rabbit iris-ciliary bodies. Because lisuride pretreatment caused no change in isoproterenol-stimulated cAMP accumulation in isolated iris-ciliary bodies, suppression of adenylate cyclase was unlikely. It is concluded that the ocular hypotensive effect of lisuride results, in part, from activation of prejunctional dopaminergic receptors on peripheral sympathetic nerves in the anterior segment of the eye but may also involve antagonism on peripheral postjunctional alpha1 adrenoceptors as well. Bilateral increases in pupil diameter antagonized by metoclopramide suggest a stimulatory action of lisuride on dopamine receptors in the central nervous system.

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.

Influence of intravitreal injections of HPMPC and related nucleoside analogues on intraocular pressure in guinea pig eyes

PURPOSE

Cidofovir (HPMPC) is a potent long-acting anticytomegalovirus agent. In humans, its dose-limiting intravitreal toxicity results in the lowering of intraocular pressure (IOP). The purpose of the present study was to determine the effects of HPMPC and various acyclic nucleoside phosphonate (ANP) analogues when administered intravitreally in guinea pig eyes and to establish the structural and functional relation of these compounds in connection with their effects on the ciliary body and retina.

METHODS

Ninety-six guinea pig eyes were injected with various doses of HPMPC and ANP analogues.

RESULTS

Severe lowering of IOP with structural alterations of the ciliary body was observed when doses were administered that achieved final intravitreal concentrations greater than 25 microg/ml HPMPC, 200 microg/ml cyclic HPMPC (cHPMPC), 25 microg/ml (S)-HPMPA, and 625 microg/ml PMEG. Concentrations of 25 microg/ml HPMPC, 200 microg/ml cHPMPC or less, and all concentrations of (R)-HPMPA, HPMPU, PMEA, PMEC, PMEDAP, (R)-PMPA, and (S)-PMPA did not lower IOP significantly, nor did they cause significant histologic changes.

CONCLUSIONS

Of the HPMP series, the cyclic analogue of HPMPC (cHPMPC) and HPMPC are the least toxic of the compounds that show potent anti-human cytomegalovirus activity (HCMV). PMEG, the most potent anti-HCMV compound of the PME series, is toxic at higher doses. Further evaluation of lower doses is needed. Compounds of the PMP series are not toxic, but they show no anti-HCMV activities. The IOP-lowering effect of these compounds appears to be associated with an effect on the ciliary body.

Anterior uveitis and hypotony after intravenous cidofovir for the treatment of cytomegalovirus retinitis

OBJECTIVE

This study aimed to describe the incidence and risk factors for the development of anterior uveitis in patients receiving intravenous cidofovir for the treatment of longstanding cytomegalovirus retinitis.

DESIGN

The study design was a retrospective cohort.

PARTICIPANTS

Eighteen patients (30 eyes) receiving parenteral cidofovir for the treatment of complicated cytomegalovirus retinitis participated.

MAIN OUTCOME MEASURES

The clinical response to parenteral cidofovir; the occurrence of anterior uveitis, and the management and outcome of patients with this complication; and the effect of cidofovir on intraocular pressure measurements were measured.

RESULTS

There was no progression or relapse of retinitis in patients receiving intravenous cidofovir. Eight (44%) of the 18 patients developed anterior uveitis, which occurred after a median of 4 doses of intravenous cidofovir. The median CD4+ cell count at the time of development of iritis was 101/mm3. Patients who developed uveitis had a mean increase in serum creatinine over baseline measurements (P = 0.05). The use of human immunodeficiency virus type-1 (HIV-1) protease inhibitors was not different between both groups of patients (P = 1.0). The development of anterior uveitis and visually significant hypotony necessitated withdrawal of cidofovir in only one patient.

CONCLUSIONS

Anterior uveitis was a common complication after intravenous cidofovir therapy. Despite the frequency of this complication, continued treatment with intravenous cidofovir was possible in the majority of patients. Patients with anterior uveitis after intravenous cidofovir may be treated successfully with topical corticosteroid therapy and cycloplegic agents.

Inhibition of pilocarpine-induced aqueous humor flare, hypotony, and miosis by topical administration of anti-inflammatory and anesthetic drugs to dogs

OBJECTIVE

To investigate the mechanism by which pilocarpine causes increased aqueous humor (AH) flare, hypotony, and miosis in dogs.

ANIMALS

6 dogs with normal eyes.

PROCEDURE

Both eyes of each dog were treated topically with a 2% solution of pilocarpine, and 1 eye of each dog was additionally treated with commercially available ophthamic solutions. Breakdown of the blood-aqueous barrier (BAB) was quantitated in each eye, using laser flaremetry to measure AH flare. Intraocular pressure and pupil size were also measured.

RESULTS

Pilocarpine caused increased flare from BAB breakdown that was inhibited by the drugs tested. Inhibition (most to least) of BAB breakdown was flurbiprofen more than diclofenac, proparacaine, or suprofen, which were more than 0.125 or 1.0% prednisolone. Inhibition appeared dose-dependent and caused consensual inhibition in the contralateral eye. Intraocular pressure was decreased only in proparacaine-treated eyes and increased in eyes treated with nonsteroidal anti-inflammatory drugs (NSAID). Flurbiprofen and proparacaine were the most effective at blocking miosis.

CONCLUSIONS

Pilocarpine produced a predictable, reproducible BAB breakdown in dogs. Miosis and increased AH flare were inhibited equally by proparacaine or NSAID, suggesting that these signs were caused by neuropeptide release into the AH from antidromic stimulation, which subsequently triggers prostaglandin production. Hypotony was inhibited only by anti-inflammatory drugs.

CLINICAL RELEVANCE

Proparacaine in combination with pilocarpine would be the best choice for treating dogs with acute glaucoma. Topical administration of NSAID should not be used to treat dogs with acute glaucoma, because they increase intraocular pressure and negate the effects of pilocarpine.

Ocular hypotension induced by intravitreally injected C-type natriuretic peptide

The purpose of the study is to determine if intravitreal injection of c-type natriuretic peptide (CNP) affects intraocular pressure (IOP), aqueous humor dynamics and guanosine 3',5'-cyclic monophosphate (cGMP) concentration in the aqueous humor of the rabbit eye. Also we investigated whether CNP-like immunoreactivities (CNP-LI) were present in porcine aqueous humor and whether CNP-LI were detected in rabbit and porcine ciliary body. The IOP was measured after intravitreal injection of 2 pmol approximately 20 nmol CNP into rabbit eyes. Aqueous humor dynamics (aqueous humor flow, outflow facility, and uveoscleral outflow) and cGMP concentration in the aqueous humor were determined at approximately 6 hr after CNP injection. The CNP concentration in aqueous was measured by radioimmunoassay in porcine eye, and CNP-LI were detected with a monoclonal antibody in porcine and rabbit eyes. Intravitreally injected CNP caused IOP reduction in a dose-dependent manner (P<0.0001) and the maximum effect was observed at 4 approximately 6 hr. CNP increased total outflow facility by approximately 35%, but did not affect aqueous humor flow or uveoscleral outflow. The cGMP concentration in the aqueous of CNP-treated eyes was about 4- to 14-fold higher than that in the contralateral untreated eyes. CNP concentration in aqueous was about 2-fold higher than that in plasma, and CNP-LI were found in non-pigmented epithelium of the ciliary body of both rabbit and porcine eyes. CNP may play an important role in the regulation of IOP.

Potential mechanisms of moxonidine-induced ocular hypotension: role of norepinephrine

In rabbit's aqueous humor, norepinephrine, epinephrine, dopamine and serotonin were detected simultaneously by a high performance liquid chromatography with electrochemical detection. Furthermore, the changes in catecholamine levels in aqueous humor were evaluated after topical application of moxonidine, an imidazoline1/alpha 2 receptor agonist, in the presence and absence of efaroxan. The level of norepinephrine in aqueous humor was reduced by moxonidine treatment. However, under the same set of conditions, there were no significant changes in the levels of dopamine, epinephrine or serotonin. Pretreatment with efaroxan antagonized moxonidine-induced suppression of norepinephrine levels. In other in vivo experiments, moxonidine caused a decrease in intraocular pressure which was antagonized by pretreatment with efaroxan. In the superior cervical ganglion preparation, norepinephrine release was increased 5-fold by the presence of a high K+ medium. The K(+)-evoked norepinephrine secretion was reduced by 55% by moxonidine. Pretreatment with efaroxan blocked the moxonidine-induced inhibition of norepinephrine release. It is concluded that inhibition of norepinephrine release from the superior cervical ganglion and suppression of aqueous norepinephrine levels contribute to the moxonidine-induced lowering of intraocular pressure. Moreover, the antagonism of moxonidine's in vivo and in vitro effects by efaroxan suggests the involvement of imidazoline1 receptors, but does not preclude activity on alpha 2 adrenoceptors.

Adverse side effects associated with latanoprost

PURPOSE

To report three different adverse reactions after initiating treatment with latanoprost.

METHOD

Serial clinical examinations of three patients were performed.

RESULTS

Adverse reactions such as ocular hypotony and choroidal effusions, recurrent cystoid macular edema, and facial rash were noted to occur within 1 to 4 weeks after starting topical latanoprost for the treatment of primary open-angle glaucoma.

CONCLUSION

Clinicians should be alerted to these possible complications of topical latanoprost therapy.

Adverse events and autopsy findings after intravitreous cidofovir (HPMPC) therapy in patients with acquired immune deficiency syndrome (AIDS)

OBJECTIVE

The purpose of the study is to evaluate the adverse events and autopsy findings in a series of consecutive 20-microg intravitreous cidofovir injections at a single institution.

DESIGN

The study design was a nonrandomized, consecutive case series.

PARTICIPANTS

Seventy-six patients with acquired immune deficiency syndrome with cytomegalovirus retinitis were studied prospectively. Sixty-three patients had 1 month's follow-up or longer, and this comprised the study group. In addition, histopathologic findings from 18 eyes of 9 patients were studied at autopsy.

INTERVENTION

A total of 296 injections of 20 microg cidofovir were given in 115 eyes. Sixty-three patients who had 246 injections in 93 eyes had 1 month's follow-up or longer for the evaluation of adverse events.

MAIN OUTCOME MEASURES

Postinjection chronic hypotony associated with permanent visual loss, transient hypotony, iritis, and its long-term sequela (posterior synechia and cataract, retinal detachment, extraocular cytomegalovirus involvement) were the outcomes of interest in this study. Additionally, light and electron microscopic studies of human eyes were performed.

RESULTS

The most severe adverse event was postinjection chronic hypotony. This phenomenon was associated with permanent visual loss. This was observed in 1% of the injections and 3% of the eyes of the patients (95% confidence interval, 0%-6%). Transient hypotony associated with mild-to-moderate visual loss developed in 14%, but vision recovered to baseline levels in these eyes subsequently. Analysis showed that transient hypotony in the injected eye could predict postinjection chronic hypotony in the fellow eye (two-tailed Fisher's exact test, P = 0.02). The incidence of iritis was 32%; posterior synechia and cataract were the long-term sequela of the iritis and developed in 19% and 11% of the eyes, respectively. The incidence of retinal detachment was lower (6%). Histopathologic evaluation of the eyes showed mild-to-moderate atrophy of the nonpigmented epithelium of the ciliary body and no other evidence of intraocular toxicity.

CONCLUSIONS

The most serious adverse event was postinjection chronic hypotony, which occurred in 3% of eyes. Episodes of transient hypotony appear to indicate that the fellow eye was predisposed to chronic hypotony. Therefore, it may be prudent to give intravitreous injections at least 2 weeks apart in the fellow eye to evaluate the clinical response of the injected eye.

Ocular penetration and bioconversion of prostaglandin F2alpha prodrugs in rabbit cornea and conjunctiva

The objective of this study was to identify prostaglandin F2alpha (PGF2alpha) prodrugs that have an optimal ocular absorption profile and therefore could be potentially useful for the treatment of glaucoma. Rabbit cornea, conjunctiva, and iris/ciliary body were mounted in a flow-through chamber to evaluate the permeability and bioconversion of PGF2alpha and its prodrugs. The prodrugs tested were PGF2alpha 1-isopropyl, 1,11-lactone, 15-acetyl, 15-pivaloyl, 15-valeryl, and 11,15-dipivaloyl esters. After 4 h in the donor or acceptor compartments, the products and formation of PGF2alpha were analyzed by HPLC. Effects on intraocular pressure and ocular surface hyperemia were also determined. All prodrugs penetrated the rabbit cornea faster than PGF2alpha by 4- to 83-fold. All prodrugs penetrated conjunctiva faster than PGF2alpha, except the 15-acetyl ester prodrug, which was equally permeable. No direct correlation between drug lipophilicity and permeability across the cornea or conjunctiva was apparent. The most metabolically stable prodrug was the 1,11-lactone, followed by the 11,15-dipivaloyl, 15-pivaloyl, 15-acetyl, 1-isopropyl, and the 15-valeryl esters, the latter of which was extensively converted to PGF2alpha. A separation index for various prodrugs was calculated from the ratio of the bioavailable PGF2alpha for ocular hypotension to the bioavailable PGF2alpha for hyperemia. The highest separation index was observed for the 1,11-lactone prodrug (2.33), followed by the 11,15-dipivaloyl ester prodrug (1.80). Thus the 1,11-lactone and 11,15-dipivaloyl ester prodrugs appeared to be superior to the others in providing bioavailable PGF2alpha for ocular hypotension, while minimizing hyperemia. The favorable separation index for these compounds appeared to be due to their metabolic stability at the corneal surface and conjunctiva combined with sufficient bioavailability for ocular hypotension.

Pharmacological evidence for thromboxane receptor heterogeneity--implications for the eye

The pharmacological activity of two novel thromboxane A2 (TxA2)-mimetics, AGN191976 and AGN192093, was investigated in vitro, using standard organ bath assays and human platelets, to determine potency and selectivity at various prostanoid (PG-) receptors. The effects of these compounds on intraocular pressure in Beagle dogs were then compared with U-46619, a widely employed and structurally different TP-receptor agonist. AGN191976 and AGN192093 were highly potent TP-receptor agonists in the rat aorta (EC50 of 0.32 and 1.3 nM, respectively) and human myometrium. Both compounds were approximately 10 to 50 fold more potent than U-46619. These contractile responses could be blocked with a potent TP-receptor antagonist, SQ29548. In human platelets, AGN191976 (EC50 = 16.3 nM) and U-46619 (EC50 = 538.3 nM) potently stimulated aggregation (TP-receptor mediated effect), whereas AGN192093 was a much weaker agonist (EC50 = 37.9 microM). AGN192093 was not a partial agonist in platelets, since it did not antagonize aggregation induced by AGN191976, U-46619, arachidonic acid or ADP. These results provide evidence for a subdivision of TP-receptors, and AGN192093 appears to be able to distinguish between TP-receptors in smooth muscle and platelets. In the Beagle dog eye, both AGN191976 and AGN192093 were highly potent and efficacious ocular hypotensives. Single 2.5 micrograms doses of drug decreased IOP by 11.4 (AGN191976) and 7.7 mm Hg (AGN192093) relative to the contralateral control eye. In contrast, U-46619 did not lower IOP. AGN191976, but not U-46619, increased outflow facility in these animals, which is consistent with their effects on IOP. Neither compound caused miosis which is FP-receptor mediated in the dog. These studies suggest the existence of heterogeneous populations of TP-receptors. AGN191976 and AGN192093, two novel TP-receptor agonists, appear to be useful tools for the pharmacological distinction of TP-receptor subtypes.

Enhanced ocular hypotensive response to epinephrine in rabbits with prior dexamethasone treatment

The purpose of this study was to determine glucocorticoid modulation of ocular pressure to epinephrine applied topically to rabbit eyes that were pretreated with dexamethasone. Rabbit eyes were pretreated with five applications of topical 0.07% dexamethasone (0.1% dexamethasone phosphate) or saline drops, administered at ten minute intervals. The eyes were then treated with epinephrine bitartrate drops at concentrations of free base epinephrine of 1.1%, 0.27%, 0.05%, 0.027%, 0.005% or 0.0005%. An additional group of rabbits received dexamethasone pretreatment only. Intraocular pressure (IOP) was measured for the next four hours. Enhanced lowering of intraocular pressure was observed with dexamethasone pretreatment. Rabbits receiving the smaller dose of epinephrine with dexamethasone had the largest decrease in IOP at 135 minutes after instillation of the epinephrine drops (0.005% epinephrine, mean difference +/- standard error of mean = 5.4 +/- 1.1 mmHg). Similarly, the duration of significant decrease of the IOP was prolonged in the groups receiving the lower concentrations of epinephrine (0.005% epinephrine, 255 minutes after administration of epinephrine). The synergism between glucocorticoids and adrenergic agonists in lowering IOP may be potentially useful in the therapy of ocular hypertension and glaucoma.

Latanoprost and physostigmine have mostly additive ocular hypotensive effects in human eyes

OBJECTIVE

To investigate if a pronounced ciliary muscle contraction, induced by physostigmine salicylate, can abolish the ocular hypotensive effect of latanoprost, a prostaglandin analogue, via inhibition of the uveoscleral outflow.

DESIGN

A randomized, crossover study that was double-masked for latanoprost. Physostigmine was the second factor in a 2(2) factorial experiment.

PARTICIPANTS

A total of 20 male and female healthy volunteers (median age, 25 years; age range, 17-30 years).

INTERVENTIONS

Between 7 AM and 7 PM, 1 drop of physostigmine salicylate (8 mg/mL) was instilled in 1 eye every other hour. At 8 AM, 1 drop of either latanoprost (50 mg/L) or placebo was instilled in both eyes. This protocol was repeated a second time with latanoprost administered to previously placebo-treated eyes and vice versa.

MAIN OUTCOME MEASURES

Intraocular pressure differences were measured with Goldmann applanation tonometry hourly for 13 hours.

RESULTS

Latanoprost reduced the intraocular pressure significantly at 3 to 12 hours after application with a maximal effect at 8 hours after the administration of the dose. The reduction that was obtained with physostigmine administered every other hour was more pronounced, was observed at 1 hour after the administration of the first dose, and increased throughout the day. A significant interaction was seen between 3 and 6 PM (i.e., at 7-10 hours after application of latanoprost).

CONCLUSIONS

Latanoprost and physostigmine have a mainly additive ocular hypotensive effect. Thus, high doses of physostigmine did not abolish the eye pressure-lowering effect of latanoprost, but some interaction was seen at low intraocular pressures. It was concluded that any mechanical effect on the uveoscleral flow achieved with physostigmine is short-lasting compared with the effect obtained with latanoprost, and that latanoprost and miotics can be combined.

Ocular activity of topically administered anandamide in the rabbit

Marijuana and its psychoactive constituents, cannabinoids, reduce intraocular pressure (IOP) in humans and animals. Because anandamide, a recently discovered endogenous ligand of cannabinoid receptors, reportedly shows cannabimimetic pharmacological activity, we examined its effect on the eye. Varying amounts of anandamide, in 50 microL of light mineral oil, were topically applied to a rabbit eye and changes in IOP and ocular symptoms were monitored. Anandamide (50 micrograms to 1 mg) induced a significant decrease in IOP within 1 hour after administration; maximum reduction occurred at 2 hours; and there was a return to baseline by 7 hours following administration. A noticeable hyperemia of conjunctival blood vessels was also noted 2 hours after administration. Neither mineral oil alone or with palmitylethanolamide (an analogue of anandamide) caused a significant decrease in IOP or conjunctival hyperemia. This study indicates that anandamide does produce cannabimimetic effect in rabbit eyes.

[The effect of heterogeneous scleral transplantation on hypotony after filtration surgery of glaucoma with mitomycin C]

OBJECTIVE

The study was designed to observe the effect of heterogeneous scleral transplantation in treatment of hypotony after filtration surgery of glaucoma with mitomycin C.

METHOD

7 patients (8 eyes) with hypotony after filtration surgery of glaucoma with mitomycin C were treated by heterogeneous scleral transplantation.

RESULTS

The post-operative follow-up periods ranged from 3 to 19 months (mean 7.75 +/- 5.37 months). Postoperatively, the visual acuity was increased in 5 eyes, and the intraocular pressure was increased to normal level in all eight eyes.

CONCLUSION

Heterogeneous scleral transplantation has therapeutic effects in the treatment of hypotonic eyes after filtration surgery of glaucoma.

Severe visual loss after autologous blood injection for mitomycin-C-associated hypotonous maculopathy

It has been shown that mitomycin-C increases the success rate of trabeculectomy; however, a rise in the incidence of postoperative complications has also been reported. Consequently, the use of antimetabolite is usually reserved for patients who are at high risk of surgical failure or for patients with advanced glaucoma in whom low intraocular pressure is desired. This report describes a patient who suffered severe visual loss which was a direct result of hypotonous maculopathy after trabeculectomy with mitomycin-C and various other complications from the subsequent interventions.

Mitomycin-C in laser sclerostomy: benefit and complications

BACKGROUND AND OBJECTIVE

The authors studied the effect of topical mitomycin-C administration on the maintenance of filter function and intraocular pressure (IOP) following laser sclerostomy.

PATIENTS AND METHODS

Twenty-six patients with a presumed high risk of episcleral scarring were treated intraoperatively with topical mitomycin-C (0.5 mg/ml) for 3 to 5 minutes. Their IOPs were monitored for at least 2 years. The IOP data of these patients were compared with the results for 46 patients who underwent the identical procedure without antimetabolite.

RESULTS

IOPs below 23 mm Hg were achieved in 70% of the mitomycin-C-treated patients. Compared with the non-mitomycin-C group, the rate and duration of early postoperative hypotony was significantly increased in the mitomycin-C-treated group.

CONCLUSION

Mitomycin-C is useful for maintaining successful filter function in patients with unfavorable prognoses. However, severe and persistent hypotony may occur.

Ocular hypotensive mechanism of intravitreally injected brain natriuretic peptide in rabbit

PURPOSE

To determine whether brain natriuretic peptide (BNP) affects intraocular pressure (IOP), aqueous humor dynamics, and cyclic guanosine monophosphate (cGMP) concentration in the aqueous humor of the rabbit eye.

METHODS

Twenty microliters of 10(-4) M and 10(-5) M (2 nmol, 0.2 nmol) BNP or atrial natriuretic peptide (ANP) were injected intravitreally into rabbit eyes, after which the IOP was measured using a pneumatonometer. Aqueous humor dynamics were studied at approximately 6 hours after the intravitreal injection of 2 nmol BNP. Aqueous humor flow was measured by fluorophotometry, and outflow facility was measured by the two-level constant pressure perfusion method, whereas uveoscleral outflow was measured by the fluorescein isothiocyanate-dextran perfusion method. The concentration of cGMP in the aqueous humor at 6 hours after injection of 2 or 0.2 nmol BNP also was measured by enzyme immunoassay.

RESULTS

Intravitreal administration of BNP or of ANP caused a decrease in IOP, with a maximum effect at approximately 6 hours after the injection. Total outflow facility in eyes treated with 2 nmol BNP increased by 29%, although the aqueous humor flow and uveoscleral outflow did not show significant changes. The concentration of cGMP in the aqueous humor increased significantly in BNP-treated eyes.

CONCLUSIONS

Intravitreal injection of BNP into rabbit eyes reduced IOP because of an increase in the outflow facility. Brain natriuretic peptide also increased the concentration of cGMP in the aqueous humor. It is probable that BNP-activated guanylate cyclase induced an upregulation of cGMP in the aqueous humor.