Review of alpha adrenoceptor function in the eye

Implications of Ocular Confounding Factors for Aqueous Humor Proteomic and Metabolomic Analyses in Retinal Diseases

Purpose

To assess the impact of ocular confounding factors on aqueous humor (AH) proteomic and metabolomic analyses for retinal disease characterization.

Methods

This study recruited 138 subjects (eyes): 102 with neovascular age-related macular degeneration (nAMD), 18 with diabetic macular edema (DME), and 18 with cataract (control group). AH samples underwent analysis using Olink Target 96 proteomics and Metabolon's metabolomics platform Data analysis included correlation, differential abundance, and gene-set analysis.

Results

In total, 756 proteins and 408 metabolites were quantified in AH. Total AH protein concentration was notably higher in nAMD (3.2-fold) and DME (4.1-fold) compared to controls. Pseudophakic eyes showed higher total AH protein concentrations than phakic eyes (e.g., 1.6-fold in nAMD) and a specific protein signature indicative of matrix remodeling. Unexpectedly, pupil-dilating drugs containing phenylephrine/tropicamide increased several AH proteins, notably interleukin-6 (5.4-fold in nAMD). Correcting for these factors revealed functionally relevant protein correlation clusters and disease-relevant, differentially abundant proteins across the groups. Metabolomics analysis, for which the relevance of confounder adjustment was less apparent, suggested insufficiently controlled diabetes and chronic hyperglycemia in the DME group.

Conclusions

AH protein concentration, pseudophakia, and pupil dilation with phenylephrine/tropicamide are important confounding factors for AH protein analyses. When these factors are considered, AH analyses can more clearly reveal disease-relevant factors.

Translational Relevance

Considering AH protein concentration, lens status, and phenylephrine/tropicamide administration as confounders is crucial for accurate interpretation of AH protein data.

Adrenaline blocks key cell cycle genes and exhibits antifibrotic and vasoconstrictor effects in glaucoma surgery

Adrenaline is a sympathomimetic drug used to maintain pupil dilation and to decrease the risk of bleeding. The aim of this study was to demonstrate if adrenaline could exert antifibrotic effects in glaucoma surgery. Adrenaline was tested in fibroblast-populated collagen contraction assays and there was a dose-response decrease in fibroblast contractility: matrices decreased to 47.4% (P = 0.0002) and 86.6% (P = 0.0036) with adrenaline 0.0005% and 0.01%, respectively. There was no significant decrease in cell viability even at high concentrations. Human Tenon's fibroblasts were also treated with adrenaline (0%, 0.0005%, 0.01%) for 24 h and RNA-Sequencing was performed on the Illumina NextSeq 2000. We carried out detailed gene ontology, pathway, disease and drug enrichment analyses. Adrenaline 0.01% upregulated 26 G1/S and 11 S-phase genes, and downregulated 23 G2 and 17 M-phase genes (P < 0.05). Adrenaline demonstrated similar pathway enrichment to mitosis and spindle checkpoint regulation. Adrenaline 0.05% was also injected subconjunctivally during trabeculectomy, PreserFlo Microshunt and Baerveldt 350 tube surgeries, and patients did not experience any adverse effects. Adrenaline is a safe and cheap antifibrotic drug that significantly blocks key cell cycle genes when used at high concentrations. Unless contraindicated, we recommend subconjunctival injections of adrenaline (0.05%) in all glaucoma bleb-forming surgeries.

Effect of Topical Dexmedetomidine (0.0055%) on Intraocular Pressure in Healthy Eyes: A Randomized Controlled Trial

Aim and objective

Evaluate the short-term safety and efficacy of dexmedetomidine (0.0055%) drops on intraocular pressure (IOP) in healthy eyes.

Materials and methods

In this randomized controlled trial, patients with normal eye exams were randomly assigned to receive, in a randomly selected eye, one drop of either balanced salt solution (BSS) or dexmedetomidine (0.0055%). Goldmann applanation tonometry was performed at baseline and then 30 minutes, 4 hours, and 24 hours after drop instillation.

Results

Forty-nine eyes of 49 normal volunteers were enrolled in the study, with 21 eyes (group I) receiving BSS and 28 (group II) dexmedetomidine. Both groups were comparable at baseline as far as age and IOP (p = 0.55 for both parameters). Intraocular pressure significantly decreased from baseline in group II at 30 minutes and 4 hours (p = 0.001 and 0.05, respectively). Maximum IOP decrease was obtained at 30 minutes after dexmedetomidine instillation, with a 9% decrease from baseline (mean decrease: 1.15 mm Hg). The percentage of IOP decrease was significantly higher in group II at 30 minutes compared with group I (9 vs 1.1%; p = 0.05). No side effects were recorded.

Conclusion

In this pilot study, dexmedetomidine 0.0055% drops have shown good safety and efficacy in lowering IOP in normal healthy volunteers with no history of glaucoma. This medication has a short onset of action, with a 10% reduction of IOP occurring 30 minutes post-instillation.

Trial registration number

NCT03690622.

How to cite this article

Fakhoury H, Abdelmassih Y, El-Khoury S, et al. The Effect of Topical Dexmedetomidine (0.0055%) on Intraocular Pressure in Healthy Eyes: A Randomized Controlled Trial. J Curr Glaucoma Pract 2021;15(2):58-63.

Safety of Once-Daily Oxymetazoline HCl Ophthalmic Solution, 0.1% in Patients with Acquired Blepharoptosis: Results from Four Randomized, Double-Masked Clinical Trials

Purpose

An oxymetazoline 0.1% ophthalmic solution was recently approved for treatment of acquired blepharoptosis in adults. This study's objective was to evaluate the safety profile of oxymetazoline 0.1% when administered once daily for 14-84 days.

Patients and Methods

Pooled analysis examined safety outcomes from four randomized, double-masked, placebo-controlled clinical trials conducted at 6, 16, 27, and 35 sites, respectively, in the United States. In total, 568 participants with acquired blepharoptosis were evaluated. Median age was 66 years and 74.8% of participants were female. Overall, 375 participants self-administered oxymetazoline 0.1% to both eyes once/day and 193 self-administered placebo (vehicle) daily. Treatment-emergent adverse event (TEAE) rates, severity, and causality were evaluated in the overall population and within participant subgroups defined based on age, race, and ethnicity. Vital signs and ophthalmic findings were evaluated at predefined study visits. Patient-reported treatment tolerability was recorded at study end.

Results

TEAE incidence was similar among participants using oxymetazoline 0.1% (31.2%) or vehicle (30.6%). Nearly all TEAEs were mild-to-moderate, and most were not suspected of being treatment related. Serious TEAEs occurred in four participants receiving oxymetazoline 0.1% and one participant receiving vehicle. Nine and two participants in the oxymetazoline 0.1% and vehicle groups, respectively, discontinued due to a TEAE. Ocular TEAEs occurring in ≥2% of participants receiving oxymetazoline 0.1% were punctate keratitis, conjunctival hyperemia, dry eye, blurred vision, instillation site pain, and corneal vital dye staining, with none occurring in >3.5% of participants. TEAE rates were similar across subgroups based on age, race, and ethnicity. No clinically significant mean changes in vital signs or ophthalmologic findings occurred, and >98% of participants rated oxymetazoline 0.1% as causing no/mild discomfort.

Conclusion

Once-daily oxymetazoline 0.1% was safe and well tolerated in participants with acquired blepharoptosis when used for 14-84 days. Safety did not appear to differ based on age, race, or ethnicity.

Association of Oxymetazoline Hydrochloride, 0.1%, Solution Administration With Visual Field in Acquired Ptosis: A Pooled Analysis of 2 Randomized Clinical Trials

Importance

Treatment of acquired blepharoptosis (ptosis) is currently limited to surgical intervention.

Objective

To examine the efficacy and safety of oxymetazoline hydrochloride, 0.1%, ophthalmic solution (oxymetazoline, 0.1%) in participants with acquired ptosis.

Design, Setting, and Participants

This pooled analysis of 2 randomized, double-masked, placebo-controlled, multicenter phase 3 clinical trials included participants 9 years and older with acquired ptosis and superior visual field deficit. The 2 studies were conducted across 16 and 27 sites in the United States. Patients were enrolled from May 2015 to April 2019. Analyses for the individual trials were initiated after database lock and completed on September 6, 2017, and May 16, 2019. Pooled analysis was completed on August 25, 2019.

Interventions

Participants (randomized 2:1) received oxymetazoline, 0.1%, or vehicle, self-administered as a single drop per eye, once daily, for 42 days.

Main Outcomes and Measures

The primary efficacy end point was change from baseline in the number of points seen on the Leicester Peripheral Field Test, a test to detect superior visual field deficits due to ptosis, on days 1 (6 hours after instillation) and 14 (2 hours after instillation). The secondary end point, change from baseline in marginal reflex distance 1, was assessed at the same time points.

Results

In total, 304 participants were enrolled (mean [SD] age, 63.8 [13.8] years; 222 women [73%]). Overall, 97.5% (198 of 203) of participants receiving oxymetazoline, 0.1%, and 97.0% (98 of 101) of participants receiving vehicle completed the studies. Oxymetazoline, 0.1%, was associated with a significant increase in the mean (SD) number of points seen on the Leicester Peripheral Field Test vs vehicle (day 1: 5.9 [6.4] vs 1.8 [4.1]; mean difference, 4.07 [95% CI, 2.74-5.39]; P < .001; day 14: 7.1 [5.9] vs 2.4 [5.5]; mean difference, 4.74 [95% CI, 3.43-6.04]; P < .001). Oxymetazoline, 0.1%, also was associated with a significant increase in marginal reflex distance 1 from baseline (mean [SD]: day 1: 0.96 [0.89] mm vs 0.50 [0.81] mm; mean difference, 0.47 mm [95% CI, 0.27-0.67]; P < .001; day 14: 1.16 [0.87] mm vs 0.50 [0.80] mm; mean difference, 0.67 mm [95% CI, 0.46-0.88]; P < .001). Treatment-emergent adverse events (TEAEs) occurred in 31.0% (63 of 203) of participants receiving oxymetazoline, 0.1%, and 35.6% (36 of 101) of participants receiving vehicle. Among participants receiving oxymetazoline, 0.1%, with a TEAE, 81% (51 of 63) had a maximum TEAE intensity of mild, and 62% (39 of 63) had no TEAE suspected of being treatment related.

Conclusions and Relevance

Oxymetazoline, 0.1%, was associated with positive outcomes and was well tolerated in phase 3 trials after instillation at days 1 and 14, demonstrating its potential promise for the treatment of acquired ptosis, although further study is needed to elucidate the clinical relevance of these findings beyond 6 weeks.

Advances in the discovery of novel agents for the treatment of glaucoma

INTRODUCTION

Glaucoma, a neuropathy characterized by increased intraocular pressure (IOP), is the major cause of blindness worldwide and its treatment aims at reducing IOP.

AREAS COVERED

The authors review the design of the main classes of anti-glaucoma agents. Drugs which interfere with the aqueous humor secretion (adrenergic agonists/antagonists, carbonic anhydrase inhibitors) and with its outflow, by means of both conventional and non-conventional pathways (prostaglandin (PG) analogs, rho kinase inhibitors, nitric oxide (NO) donors) as well as new agents (adenosine receptors modulators, melatonin - fatty acid amide hydrolase hybrids, tyrosine kinase activators, natriuretic peptide analogs) are considered.

EXPERT OPINION

The anti-glaucoma drug field has undergone several developments in recent years with the approval of at least three new drugs belonging to novel pharmacological classes, the rho kinase inhibitors ripasudil and netarsudil, and the PG-NO donor hybrid latanoprostene bunod. Eye drops with combinations of two different drugs are also available, allowing for effective IOP control, with once daily administration for some of them, which assures a better patient compliance and ease of administration. Overall, after more than a decade without new anti-glaucoma drugs, the last year afforded interesting new pharmacological opportunities for the management of this disease.

Investigation of the effects of orally administered trazodone on intraocular pressure, pupil diameter, physical examination variables, and sedation level in healthy equids

OBJECTIVE

To investigate the effects of orally administered trazodone on intraocular pressure (IOP), pupil diameter measured in the vertical plane (ie, vertical pupil diameter [VPD]), selected physical examination variables, and sedation level in healthy equids.

ANIMALS

7 horses and 1 pony.

PROCEDURES

Food was withheld for 12 hours prior to drug administration. After baseline (time 0) sedation scoring, physical examination, and measurement of IOP and VPD, equids received 1 dose (approx 6 mg/kg) of trazodone orally. Examination and measurement procedures were repeated 0.5, 1, 2, 4, 8, 12, and 24 hours after drug administration. Blood samples were collected at each time point for analysis of plasma trazodone concentrations. Repeated-measures analysis was used to compare examination results between downstream time points and baseline.

RESULTS

7 of 8 equids had mild sedation from 0.5 to 8 hours after treatment; compared with baseline values, mean IOP was significantly lower from 0.5 hours to 8 hours, mean VPD was significantly smaller at 0.5 hours, and mean rectal temperature was significantly lower from 1 to 8 hours after drug administration. Adverse effects (signs of excitement in 1 equid and sweating in 4) were self-limiting and considered minor. Mean maximum plasma concentration of trazodone was 1,493 ng/mL 0.75 hours after administration, and terminal half-life of the drug was 9.96 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

The described oral dose of trazadone elicited sedation with a few self-limiting adverse effects in the study sample. Drug effects on IOP and VPD may alter ocular examination findings. Further investigation is warranted prior to use of trazodone for sedation in equids, particularly those with ophthalmic conditions.

Phentolamine Mesylate Ophthalmic Solution Provides Lasting Pupil Modulation and Improves Near Visual Acuity in Presbyopic Glaucoma Patients in a Randomized Phase 2b Clinical Trial

PURPOSE

Phentolamine mesylate ophthalmic solution (PMOS), applied to the eye topically, was shown previously to have beneficial effects in patients with dim light vision disturbances (DLD), including decreased pupil diameter (PD), improved best-corrected distance visual acuity (BCDVA), as well as lower intraocular pressure (IOP). The ORION-1 trial evaluated the long-term safety and efficacy of PMOS in a glaucomatous, presbyopic population.

PATIENTS AND METHODS

In this randomized, double-masked, multi-center, placebo-controlled, multiple-dose Phase 2b trial, 39 patients with elevated IOP were randomized to receive one evening dose of study medication or placebo for 14 days. The primary outcome measure was mean change in diurnal IOP, and the key secondary outcome measures included changes in PD, distance-corrected near visual acuity (DCNVA), and conjunctival hyperemia.

RESULTS

Use of 1% PMOS did not lead to a statistically significant decrease in diurnal IOP compared to placebo (P = 0.89) but trended toward a greater decrease in patients with lower IOP baselines. PMOS produced a statistically significant mean 20% PD reduction under both photopic and mesopic conditions that was sustained for 36 hours post-dosing. A statistically significant number of patients with PMOS compared to placebo demonstrated ≥1 line of improvement in photopic DCNVA at day 8 (P = 0.0018), day 15 (P = 0.0072), and day 16 (P = 0.0163), with a trend for 2- and 3-line improvements at all time points. There was no statistical difference in conjunctival hyperemia compared to placebo.

CONCLUSION

Although mean IOP was not lowered significantly, daily evening dosing of 1% PMOS was found to be well tolerated with no daytime conjunctival redness and demonstrated improvement in DCNVA with sustained PD reduction in a glaucomatous and presbyopic population. Smaller pupil size can have beneficial effects in improving symptoms of presbyopia and DLD, which will be the focus of further studies.

Over-the-Counter Ocular Decongestants in the United States - Mechanisms of Action and Clinical Utility for Management of Ocular Redness

To manage ocular redness effectively, health-care practitioners require an understanding of the pathophysiology, clinical features and differential diagnosis of ocular redness, as well as comprehensive knowledge of medical therapies available and their pharmacologic properties. This review aims to provide a clinically relevant summary of the current literature on the mechanism of action, efficacy, and safety of current over-the-counter (OTC) decongestants available for reduction of ocular redness due to minor irritations. Currently marketed OTC products indicated for such use in the United States include topical solutions of tetrahydrozoline 0.05%, naphazoline 0.012% to 0.03%, and brimonidine 0.025%. All 3 agents are adrenergic receptor agonists but vary in their receptor-binding profiles: tetrahydrozoline is a selective α1 receptor agonist; naphazoline is a mixed α1/α2 receptor agonist; and brimonidine is a selective α2 receptor agonist. These OTC decongestants produce vasoconstriction of conjunctival blood vessels, which results in a rapid reduction in ocular redness. In general, ocular adverse events reported in published studies of these OTC decongestants were minimal, mild, and transient, with no significant adverse systemic effects. However, ocular decongestants with α1-adrenergic receptor agonist activity can be associated with loss of effectiveness with continued use (ie, tachyphylaxis) and rebound redness upon treatment discontinuation. In clinical trials of the selective α2-adrenergic receptor agonist brimonidine 0.025%, tachyphylaxis was not observed, and rebound redness was rarely reported.

High-dose phenylephrine increases meningeal blood flow through TRPV1 receptor activation and release of calcitonin gene-related peptide

BACKGROUND

The α₁ -adrenoceptor agonist, phenylephrine, is used at high concentrations as a mydriatic agent and for the treatment of nasal congestion. Among its adverse side-effects transient burning sensations are reported indicating activation of the trigeminal nociceptive system.

METHODS

Neuropeptide release, calcium imaging and meningeal blood flow recordings were applied in rodent models of meningeal nociception to clarify possible receptor mechanisms underlying these pain phenomena.

RESULTS

Phenylephrine above 10 mM dose-dependently released calcitonin gene-related peptide (CGRP) from the dura mater and isolated trigeminal ganglia, whereas hyperosmotic mannitol at 90 mM was ineffective. The phenylephrine-evoked release was blocked by the transient receptor potential vanilloid 1 (TRPV1) antagonist BCTC and did not occur in trigeminal ganglia of TRPV1-deficient mice. Phenylephrine at 30 mM caused calcium transients in cultured trigeminal ganglion neurons responding to the TRPV1 agonist capsaicin and in HEK293T cells expressing human TRPV1. Local application of phenylephrine at micromolar concentrations to the exposed rat dura mater reduced meningeal blood flow, whereas concentrations above 10 mM caused increased meningeal blood flow. The flow increase was abolished by pre-application of the CGRP receptor antagonist CGRP_8-37 or the TRPV1 antagonist BCTC.

CONCLUSIONS

Phenylephrine at high millimolar concentrations activates TRPV1 receptor channels of perivascular afferents and, upon calcium inflow, releases CGRP, which increases meningeal blood flow. Activation of TRPV1 receptors may underlie trigeminal nociception leading to cranial pain such as local burning sensations or headaches caused by administration of high doses of phenylephrine.

SIGNIFICANCE

Phenylephrine is used at high concentrations as a mydriaticum and for treating nasal congestion. As adverse side-effects burning sensations and headaches have been described. Phenylephrine at high concentrations causes calcium transients in trigeminal afferents, CGRP release and increased meningeal blood flow upon activation of TRPV1 receptor channels, which is likely underlying the reported pain phenomena.

Targeted Drug Delivery Systems for the Treatment of Glaucoma: Most Advanced Systems Review

Each year, new glaucoma drug delivery systems are developed. Due to the chronic nature of the disease, it requires the inconvenient daily administration of medications. As a result of their elution from the eye surface and penetration to the bloodstream through undesired permeation routes, the bioavailability of active compounds is low, and systemic side effects occur. Despite numerous publications on glaucoma drug carriers of controlled drug release kinetics, only part of them consider drug permeation routes and, thus, carriers' location, as an important factor affecting drug delivery. In this paper, we try to demonstrate the importance of the delivery proximal to glaucoma drug targets. The targeted delivery can significantly improve drug bioavailability, reduce side effects, and increase patients' compliance compared to both commercial and scientifically developed formulations that can spread over the eye surface or stay in contact with conjunctival sac. We present a selection of glaucoma drug carriers intended to be placed on cornea or injected into the aqueous humor and that have been made by advanced materials using hi-tech forming methods, allowing for effective and convenient sustained antiglaucoma drug delivery.

Adrenergic agonists and antagonists as antiglaucoma agents: a literature and patent review (2013-2019)

Introduction: Glaucoma is a neurodegenerative disease of the eye characterized by selective retinal ganglion cell loss that provokes progressive defects in the visual field. Elevated intraocular pressure (IOP) is an important contributor for the progression of glaucoma. The current therapeutic arsenal for reducing IOP includes prostaglandin analogs, β-blockers, carbonic anhydrase inhibitors, α-adrenergic agonist, miotics, rho-kinase inhibitors and combinations thereof, generally administered as eye drops. Areas covered: This manuscript reviews the state of art on adrenergic modulators for treating glaucoma. Both monotherapy and fixed-drugs combinations including α₂-adrenergic agonists and β-blockers are discussed as well as drug delivery systems where these classes of drugs are used. The review then covers the patent literature involving adrenoceptors modulators over the period 2013-2019. Expert opinion: While the scientific community is moving forward novel targets and related modulators for treating glaucoma and ocular hypertension, adrenergic modulators held a prominent position in the therapy of glaucoma and related disorders. Indeed, though not embodying anymore the first-choice monotherapy, they are widely marketed worldwide ordinarily in combination with other drugs, are subjects of many studies for identifying new drug compositions and have been assessed as active ingredients in several innovative ocular drug delivery systems.

GPR158 in the Visual System: Homeostatic Role in Regulation of Intraocular Pressure

Purpose: GPR158 is a newly characterized family C G-protein-coupled receptor, previously identified in functional screens linked with biological stress, including one for susceptibility to ocular hypertension/glaucoma induced by glucocorticoid stress hormones. In this study, we investigated GPR158 function in the visual system. Methods: Gene expression and protein immunolocalization analyses were performed in mouse and human brain and eye to identify tissues where GPR158 might function. Gene expression was perturbed in mice, and in cultures of human trabecular meshwork cells of the aqueous outflow pathway, to investigate function and mechanism. Results: GPR158 is highly expressed in the brain, and in this study, we show prominent expression specifically in the visual center of the cerebral cortex. Expression was also observed in the eye, including photoreceptors, ganglion cells, and trabecular meshwork. Protein was also localized to the outer plexiform layer of the neural retina. Gpr158 deficiency in knockout (KO) mice conferred short-term protection against the intraocular pressure increase that occurred with aging, but this was reversed over time. Most strikingly, the pressure lowering effect of the acute stress hormone, epinephrine, was negated in KO mice. In contrast, no disruption of the electroretinogram was observed. Gene overexpression in cell cultures enhanced cAMP production in response to epinephrine, suggesting a mechanism for intraocular pressure regulation. Overexpression also increased survival of cells subjected to oxidative stress linked to ocular hypertension, associated with TP53 pathway activation. Conclusions: These findings implicate GPR158 as a homeostatic regulator of intraocular pressure and suggest GPR158 could be a pharmacological target for managing ocular hypertension.

A common humoral background of intraocular and arterial blood pressure dysregulation

BACKGROUND

It has been postulated that intraocular pressure, an important glaucoma risk factor, correlates positively with arterial blood pressure (blood pressure). However, results of experimental and clinical studies are often contradictory. It is hypothesized that, in some hypertensive patients, disturbances in intraocular pressure regulation may depend on biological effects of blood borne hormones underlying a particular type of hypertension, rather than on blood pressure level itself.

REVIEW

This review compares the effects of hormones on blood pressure and intraocular pressure, in order to identify a hormonal profile of hypertensive patients with an increased risk of intraocular pressure surge. The PUBMED database was searched to identify pre-clinical and clinical studies investigating the role of angiotensin II, vasopressin, adrenaline, noradrenaline, prostaglandins, and gaseous transmitters in the regulation of blood pressure and intraocular pressure.

RESULTS

Studies included in the review suggest that intraocular and blood pressures often follow a different pattern of response to the same hormone. For example, vasopressin increases blood pressure, but decreases intraocular pressure. In contrast, high level of nitric oxide decreases blood pressure, but increases intraocular pressure.

CONCLUSIONS

Arterial hypertension is associated with altered levels of blood borne hormones. Contradicting results of studies on the relationship between arterial hypertension and intraocular pressure might be partially explained by diverse effects of hormones on arterial and intraocular pressures. Further studies are needed to evaluate if hormonal profiling may help to identify glaucoma-prone patients.

Pharmacology of the intraocular pressure (IOP) lowering effect of systemic dexanabinol (HU-211), a non-psychotropic cannabinoid

The purpose of this study was to characterize the intraocular pressure (IOP) lowering activity and possible mechanism of action of the synthetic, non-psychotropic cannabinoid dexanabinol (HU-211) [(+)(3S,4S), 7-hydroxy-delta-6-tetrahydrocannabinol 1,1 dimethylheptyl], following intravenous (i.v.) administration in the rabbit. IOP (pneumatonometry), aqueous humor inflow rate (fluorophotometry), blood pressure, and heart rate (computerized physiograph system connected to central ear artery cannula) were measured in unanesthetized albino rabbits. Intravenous administration of HU-211 resulted in a dose-related reduction in IOP; a maximal IOP reduction of 5.0 +/- 0.2 mmHg was observed 4 hr after a 0.5 mg/kg dose. No significant changes in blood pressure or heart rate were observed during the first hr following this dose of HU-21 1. Pupil diameter did not change significantly during the 5 hr following the 0.5 mg/kg i.v. dose. No significant change in the rate of aqueous humor inflow occurred during the 6 hr after a 0.5 mg/kg dose of HU-211, thereby implicating outflow changes as the major source of IOP reduction. IOP reduction by HU-211 following pre-treatment with the alpha2 adrenergic antagonist, yohimbine (1 mg/kg, i.v.), was only 30% of that of HU-211 alone. IOP reduction following pretreatment with the alpha2 agonist, clonidine (0.5 mg/kg i.v.), was twice as large as that of HU-211 alone. Pretreatment with the beta-adrenergic antagonist, propranolol (0.5 mg/kg i.v.), resulted in a 50% reduction in the IOP-lowering effect of HU-211. In summary, HU-211, administered i.v., is an effective IOP-lowering agent, devoid of any significant side effects (blood pressure, heart rate or pupil diameter, all of which have been reported previously for cannabinoids). Involvement of the adrenergic system is indicated in mediating the IOP-lowering effects of HU-211 that appear to reflect a change in fluid outflow from the eye.

Topical naphazoline in treatment of myopathic ptosis

We instilled naphazoline Hcl (0.1%), an imidazole derivative with preferential alpha-2 activity, in 17 eyes of 12 patients with myopathic ptosis due to involvement of the levator palpebrae superioris, in the attempt to selectively stimulate Müller's smooth muscle. Naphazoline significantly widened the palpebral fissure with little change in pupillary diameter and no significant change in ocular pressure, visual acuity and near point determination. However, a reduction of the effect, probably due to tachyphylaxis, was noticed when using naphazoline regularly several times a day for few weeks. In conclusion naphazoline has powerful cosmetical and functional effects in mild to moderate myopathic ptosis above all if taken occasionally.

Ocular responses in healthy subjects to topical bunazosin 0.3%--an alpha 1-adrenoceptor antagonist

The ocular effects of the alpha-adrenoceptor blocking drug bunazosin, administered as eyedrops, have been measured in a placebo-controlled double-blind single-dose study in 15 healthy volunteers. The drug significantly reduced intraocular pressure over 10 hours, and there was no associated change in pulsatile ocular blood flow. Characteristic effects of alpha-adrenoceptor blockade were observed--miosis, ptosis, and conjunctival hyperaemia. The miosis alone persisted for more than 24 hours in nine out of 15 subjects.