Ocular effects of beta-adrenergic agents. XII Jules Stein Lecture

Mydriatic insert and intracameral injections compared with mydriatic eyedrops in cataract surgery: controlled studies

Mydriatic eyedrops are the standard method for pupil dilation in cataract surgery, but their limitations have prompted a search for alternative techniques. Two alternatives-an ophthalmic insert containing phenylephrine and tropicamide and intracameral injections of various combinations of lidocaine, cyclopentolate, and phenylephrine, with or without epinephrine in the irrigating solution-have been assessed in prospective controlled studies, including randomized controlled trials (RCTs). We reviewed the safety and efficacy of mydriatic ophthalmic inserts and intracameral mydriatic injections compared with the safety and efficacy of mydriatic eyedrops using a systematic PubMed search (1963 to 2014). We identified 9 prospective studies (7 RCTs, 637 patients) of the mydriatic ophthalmic insert and 15 prospective studies (14 RCTs, 1020 patients) of intracameral mydriatic injections; 7 of the RCTs compared intracameral mydriatic injections and mydriatic eyedrops and 7 RCTs studied the optimum intracameral mydriatic injection protocol. The latter showed that a lidocaine and phenylephrine-based solution, without irrigating epinephrine, was optimum for intracameral mydriatic injections. The mydriatic ophthalmic insert and intracameral mydriatic injections were consistently shown to be safe and as effective as mydriatic eyedrops. Each method has distinct advantages and limitations.

FINANCIAL DISCLOSURE

Dr. Behndig has received fees from Théa Pharma GmbH as a member of the European Team for the Prophylaxis of Infection in Cataract Surgery group. Dr. Korobelnik has received consultancy fees from Alcon Surgical, Inc.; Allergan, Inc.; Alimera, Inc.; Bayer HealthCare AG; Carl Zeiss Meditec AG; Novartis Corp.; Roche Innovatis AG; and Théa Pharma GmbH.

Mydriatic response to different concentrations of intracameral phenylephrine in humans

PURPOSE

To assess the mydriatic response to concentrations of intracamerally injected phenylephrine from 0.15 mg/mL to 30.00 mg/mL (0.015% to 3.000%) in human eyes.

SETTING

Department of Clinical Science/Ophthalmology, Umeå University Hospital, Umeå, Sweden.

DESIGN

Comparative case series.

METHODS

This prospective randomized double-masked study comprised patients scheduled for phacoemulsification cataract surgery. At the beginning of the procedure, patients received an intracameral injection of 0.15 mL of phenylephrine 0.15, 0.5, 1.5, 5.0, 15.0, or 30.0 mg/mL. To assess the mydriatic response, the pupil size was registered over 60 seconds using digital video recording. Then, the surgery was performed in the standard manner.

RESULTS

The study evaluated 42 patients. The mydriatic response was almost identical at the 4 lower phenylephrine concentrations (0.15 to 5.00 mg/mL; 0.015% to 0.500%), with final pupil sizes of approximately 4.3 mm. The 2 higher concentrations gave significantly larger pupils as follows: mean 5.80 mm ± 0.79 (SD) for 15.0 mg/mL (1.5%) and 6.65 mm ± 0.57 for 30.0 mg/mL (3.0%).

CONCLUSIONS

Results show that phenylephrine injected intracamerally does not have a linear mydriatic dose-response relationship in humans. At very high concentrations, phenylephrine may bind to and stimulate receptors other than the α(1)-receptor, explaining this phenomenon.

Separate and additive mydriatic effects of lidocaine hydrochloride, phenylephrine, and cyclopentolate after intracameral injection

PURPOSE

To assess the separate mydriatic effect of lidocaine hydrochloride (Xylocaine), cyclopentolate, and phenylephrine after intracameral injection and evaluate whether intracameral Xylocaine and phenylephrine without cyclopentolate provide sufficient pupil dilation for cataract surgery.

SETTING

Department of Clinical Science/Ophthalmology, Umeå University Hospital, Umeå, Sweden.

METHODS

This prospective randomized double-masked study included 56 patients with age-related cataract scheduled for unilateral phacoemulsification. In 16 patients, Xylocaine 1%, phenylephrine 1.5%, and cyclopentolate 0.1% were injected one after the other. Phenylephrine and cyclopentolate were randomized to switch in order, creating 2 study groups. An additional 40 patients were randomized to receive intracameral Xylocaine 1%, phenylephrine 1.5%, and cyclopentolate 0.1% or intracameral Xylocaine 1% and phenylephrine 1.5% only.

RESULTS

Xylocaine alone caused significant pupil dilation (mean 4.9 +/- 0.6 mm). In the group in which cyclopentolate was injected next, the pupil size increased 1.3 +/- 0.6 mm (P<.001). When phenylephrine was added, the pupil increased an additional 0.7 +/- 0.4 mm (P = .003). In the second group, in which phenylephrine was the second injection, the pupil size increased 2.1 +/- 0.5 mm (P<.001). When cyclopentolate was added, no significant change in size occurred. No statistically significant differences in pupil size were observed between the 40 patients who were given intracameral mydriatics with or without cyclopentolate.

CONCLUSIONS

Xylocaine plus phenylephrine injected intracamerally gave adequate intraoperative pupil dilation in routine phacoemulsification surgery. Cyclopentolate administrated intracamerally had no immediate additive mydriatic effect to intracameral Xylocaine combined with phenylephrine.

Intracameral mydriatics in phacoemulsification surgery obviate the need for epinephrine irrigation

PURPOSE

To evaluate the possibility of removing epinephrine from the irrigating solution in phacoemulsification surgery when using intracameral mydriatics (ICMs).

METHODS

We carried out a prospective, randomized, double-blinded study of 140 patients with age-related cataracts, scheduled for unilateral phacoemulsification. The first part of the study involved 90 patients divided into two groups. Patients in both groups were given 150 microl ICMs at the beginning of the procedure. In group 1, 0.6 microg/ml epinephrine was added to the irrigating balanced salt solution. No epinephrine was added to the irrigation solution used in group 2. The second part of the study involved 50 patients, all of whom were given topical mydriatics (TMs) and then similarly divided into two groups and treated as in the first study setting.

RESULTS

With ICMs, pupil sizes generally increased during the procedures. Remarkably, this increase was significantly greater without epinephrine (13 +/- 19% versus 4 +/- 14%; p = 0.02). In the TMs setting, pupil sizes decreased intraoperatively in both groups; significantly more without epinephrine (- 5 +/- 4% versus - 12 +/- 7%; p < 0.001).

CONCLUSIONS

An irrigating solution without epinephrine can safely be used with ICMs. The increase in pupil size during the procedure is greater without epinephrine. This study also confirms earlier findings that epinephrine is beneficial when using TMs.

Pharmacokinetics of ofloxacin in serum and vitreous humor of albino and pigmented rabbits

The purpose of this study was to evaluate the pharmacokinetics of ofloxacin in serum and vitreous humor samples from albino and pigmented rabbits by using a recently described animal model which permits robust estimation of parameter values. The drug was administered to rabbits intravenously, multiple vitreous humor and serum samples were taken from each rabbit, and the vitreous humor and serum samples were assayed by high-pressure liquid chromatography. The pharmacokinetic parameters were determined with RSTRIP, an iterative, nonlinear, weighted, least-squares regression program. Eight New Zealand White rabbits and eight Dutch Belted rabbits (split into single-dose and multiple-dose groups) were investigated in this study. The value of penetration into the vitreous humor of albino rabbits (n = 6) was 32.6% +/- 2.12%, with terminal-elimination half-life values of 3.21 and 2.39 h, respectively, for vitreous humor and serum. In pigmented rabbits after a single dose (n = 3) and with a steady-state concentration of drug in serum (n = 4), penetration values were similar, at 30.4% +/- 2.98% and 30.0% +/- 4.12%, respectively (P > 0.10). Following a single dose of ofloxacin, pigmented animals had elimination half-life values from serum and vitreous humor of 2.64 and 4.32 h, respectively. After steady state was achieved, half-life values for serum and vitreous humor were 3.12 and 6.05 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic receptors regulating vascular smooth muscle tone are only localized to the intraocular segment of the long posterior ciliary artery in bovine eye

Beta-adrenergic drugs are important drugs in glaucoma treatment. Their exact mechanism of action is not yet fully understood but a decreased perfusion pressure in the ciliary body due to blockade of vasodilatory beta-adrenoceptors is thought to participate in the reduction of intraocular pressure. This study investigates the vasodilator action of beta adrenergic-agents in intra- and extraocular arteries from bovine and human eyes. Ring segments of retinal, choroidal, intraocular segment of long posterior ciliary artery, and segments of extraocular posterior ciliary arteries from bovine eyes and short posterior ciliary arteries from freshly enucleated human eyes were mounted on an isometric myograph and their reactivity to beta-adrenergic drugs were studied. Of all vessel types examined only the intraocular segment of long posterior ciliary artery precontracted with prostaglandin F2 alpha responded to 1-isoprenaline (1 nM-1 microM) with a graded concentration-dependent relaxation (32 +/- 7%, n = 10) and a pD2 of 7.5 +/- 0.2 concentrations of 1-isoprenaline greater than 1 microM induced contractions which were antagonized by a combined blockade of alpha1- and alpha2-adrenoceptors. Salbutamol (selective beta2-agonist) induced relaxations of similar magnitude as that of 1-isoprenaline but the sensitivity of the intraocular segment of long posterior ciliary arteries to salbutamol was 312 times less than that to 1-isoprenaline, pD2 7.2 +/- 0.2 and 4.4 +/- 0.1 (n = 6), respectively, whereas dobutamine (selective beta 1-agonist) had no effect between 1 nM and 10 microM. Betaxolol (selective beta 1-antagonist) and 1CI 115811 (selective beta 2-antagonist) competitively antagonized isoprenaline-induced relaxations giving pKB-values of 5.9 +/- 0.1 (n = 11) and 8.5 +/- 0.1 (n = 6), respectively. The slope of the Schild-plots were equal to unity. Human posterior ciliary arteries with spontaneous tone or tone induced by 10 microM PGF2 alpha did not react to isoprenaline (1 nM-10 microM). The bovine intraocular segment of long posterior ciliary arteries contracted to 1-noradrenaline without alpha-adrenoceptor blockade and addition of propranolol or cocaine did not change the concentration-response curve. 1-Phenylephrine and B-HT933 induced both potent and strong contractions indicating the presence of both alpha 1- and alpha 2-adrenoceptors in these arteries. Although beta-adrenoceptors have been identified in various parts of the ocular circulation by radio-ligand binding techniques our data show that beta-adrenoceptors linked to regulation of vascular tone are only found in intraocular branches of the intraocular segment of long posterior ciliary artery in bovine eyes.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of topical beta blockers on corneal epithelial wound healing in the rabbit

Topical beta adrenergic receptor blocking agents (beta blockers) are among the most frequently prescribed ophthalmic drugs. It has been suggested that some of these agents have a toxic effect on the corneal epithelium. In the present study, four beta blockers in common therapeutic concentrations, as well as their vehicles, were applied to rabbit corneas that had undergone mechanical removal of epithelium from a 6 mm diameter corneal wound. The tested drugs (0.25% timolol, 0.25% levobunolol, 0.25% betaxolol, and 0.3% metipranolol) were found significantly to accelerate wound closure, compared with saline treatment in controls. Eyes treated with two of the vehicles (betaxolol vehicle and metipranolol vehicle) also demonstrated more rapid healing than controls, but the magnitude of the effect was not as great as that seen with the drugs. Only the beta blockers were responsible for wound closure before 60 hours, whereas the saline treated controls and vehicle treated eyes required longer times for wound closure. In this model of wound healing, beta blockers appear to have no deleterious effect on corneal epithelial wound healing.

Stimulatory and inhibitory cyclic AMP responses in rabbit ciliary processes after cervical ganglionectomy

Cyclic AMP production in response to agonists which act at a variety of receptors to either stimulate or inhibit cyclic AMP production has been studied in intact, dissected ciliary processes from rabbit eyes after unilateral surgical removal of the cervical ganglion. Cyclic AMP responses to stimulatory ligands vasoactive intestinal peptide (VIP), isoproterenol, and forskolin and inhibitory agonists neuropeptide Y (NPY), the synthetic somatostatin analogue SMS 201-995, and alpha-adrenergic agents were investigated in tissues from normal eyes and compared to the same responses in tissues from sympathetically denervated eyes. Neither stimulated cyclic AMP production nor inhibition of stimulated cyclic AMP production was significantly different in tissues from denervated vs. normal eyes. Inhibition of VIP-stimulated cyclic AMP production by epinephrine and paraaminoclonidine in tissues from both normal and denervated eyes was blocked by the alpha 2-adrenergic antagonist yohimbine but not by the alpha 1-adrenergic antagonist prazosin. These data indicate that the VIP, NPY, somatostatin, and alpha 2- and beta 2-adrenergic receptors which regulate cyclic AMP production in rabbit ciliary processes are postjunctional and suggest that ligands known to modulate cyclic AMP levels in this tissue may exert effects on aqueous humor formation independently of adrenergic innervation.

Absence of drug effects on rabbit blood-aqueous barrier permeability to non-electrolytes

The effects of either topical epinephrine, norepinephrine or pilocarpine upon the entry of non-transported radioactive solutes into the anterior or posterior chamber of pigmented rabbit eyes was examined after intravenous solute perfusion. Solutes employed were urea, thiourea, sucrose and inulin. They were infused at a rate that maintained constant plasma levels from 1 minute through 5 hours of intravenous perfusion. Anterior and posterior chamber samples were taken at either 5 minutes or 5 hours after infusion of solutes, but in either case at 1 hour after drug administration. Differences between the 5 minute and 5 hour data showed more solute entry with the passage of time, and differences were found between the rate of solute entry at both times based upon molecular size. However, while occasional statistically significant differences were found between certain drug treatments, no drug effects were noted on solute entry into the treated eye either when compared to the contralateral untreated eye or to a separate untreated control group.

Effects of adrenergic drugs on intracellular electrical potential difference of rabbit ciliary epithelial cells

The effects of adrenergic drugs on intracellular electrical potential difference (PDI) of rabbit ciliary epithelial cells were investigated. Epinephrine as well as norepinephrine hyperpolarized the PDI at lower concentrations (10(-6) M) and depolarized the PDI at higher concentrations (greater than 10(-5) M). Isoproterenol produced a depolarization of PDI and phenylephrine caused a hyperpolarization only. After pretreatment with propranolol, the change of PDI by isoproterenol was minimal. Selective agonists and antagonists were used to further characterize adrenergic effects on the PDI. Both beta 1 and beta 2 agonists caused a depolarization of PDI while both beta 1 and beta 2 antagonists produced a hyperpolarization. Alpha 1 antagonist depolarized the PDI and alpha 2 antagonist hyperpolarized the PDI. Such electrophysiological effects of the adrenergic drugs confirm the presence of alpha and beta adrenoceptors in the rabbit ciliary epithelial cells.

Alpha 2-adrenergic and VIP receptors in rabbit ciliary processes interact

The interaction between alpha 2-adrenergic and VIP receptors has been studied by examining inhibition of VIP-stimulated cyclic AMP production by adrenergic agonists in intact, excised rabbit ciliary processes. Epinephrine, norepinephrine, isoproterenol, dopamine, and the specific alpha 2-adrenergic agonists clonidine and p-aminoclonidine exhibit dose-dependent inhibition of VIP-stimulated cyclic AMP production. I50s, clonidine (0.05 microM) = p-aminoclonidine (0.05 microM) congruent to epinephrine (0.1 microM) less than norepinephrine (2.0 microM) less than isoproterenol (15 microM) = dopamine (15 microM), are consistent with the characteristic binding affinities of these adrenergic agonists for alpha 2-adrenergic receptors. Inhibition of VIP-stimulated cyclic AMP production by clonidine, epinephrine, isoproterenol, and dopamine is blocked by yohimbine but not by prazosin. These data establish the alpha 2-adrenergic specificity of the inhibitory effects observed. We have previously shown that beta 2-adrenergic receptor-mediated stimulation of cyclic AMP production in rabbit ciliary processes is also inhibited by postjunctional alpha 2-adrenergic receptors. These studies support the idea that the catecholamines may regulate aqueous humor formation by inhibiting stimulation of cyclic AMP production via postjunctional alpha 2-adrenergic receptors in ciliary processes.

Effect of adrenergic agonists on eicosanoid output from isolated rabbit choroid plexus and iris-ciliary body

Prostanoid production by rabbit choroid plexus (CP) and iris-ciliary body (ICB), and the effects of adrenergic agonists thereon, were studied in vitro. Immunoreactive prostaglandin (PG) E2 was the major prostanoid released by both tissues; the output from ICB was some two orders of magnitude greater than from CP. Immunoreactive 6-keto PGF1 alpha and thromboxane (TX) B2, the dehydration products of prostacyclin and TXA2, respectively, were detected in smaller quantities. Epinephrine stimulated the outputs of PGE2 and 6-keto PGF1 alpha, but not of TXB2, from both tissues. ICB responded to epinephrine concentrations of 10(-4) and 10(-5), while only 10(-4) was effective in stimulating prostanoid synthesis in the CP. Phenylephrine, an adrenergic agonist, stimulated prostanoid output from the ICB, but not from the CP. It is concluded that adrenergic mechanisms stimulate the biosynthesis of prostanoids in the rabbit CP and ICB. The implications of such interactions to aqueous humor and cerebrospinal fluid dynamics, or to other processes in brain and ocular physiology, are discussed.

Effects of the encircling procedure on the aqueous flow rate in retinal detachment eyes: a fluorometric study

Fluorophotometry was carried out in nine cases of unilateral non-traumatic rhegmatogenous retinal detachment successfully treated by a combination of local buckling and an encircling procedure with a silicone band. After topical instillation of fluorescein the change in its concentration in the anterior chamber was followed, from which the loss rate of the dye from the anterior chamber (k0) and the cornea-aqueous transfer coefficient (kc.ca) were estimated. The thickness of the cornea and the anterior chamber volume were also measured, and the aqueous flow rate and the corneal endothelial permeability were calculated in individual eyes. The examinations performed 4-18 months after operation showed that the aqueous flow rate in the operated eye fell to 85 (SD 12)% of that in the fellow control eye (p less than 0.005). In the operated eye the anterior chamber volume also fell significantly, and the corneal endothelial permeability may have decreased. Ocular hypotension after the detachment surgery with encirclement was attributable to a decrease in the aqueous flow rate.

Interaction between alpha 2- and beta 2-adrenergic receptors in rabbit ciliary processes

The interaction between the alpha 2- and beta 2-adrenergic receptors of ciliary processes has been studied by examining dose-response curves for adrenergic agonist stimulation of cyclic AMP production by intact, excised rabbit ciliary processes. Stimulation of cyclic AMP production by 1-isoproterenol is maximum from 0.1 to 1.0 microM; at higher concentrations stimulation decreases and approaches basal levels. Decreased cyclic AMP production at high concentrations of isoproterenol is blocked by the specific alpha 2-adrenergic antagonist, yohimbine, but not by the alpha 1-adrenergic antagonist, prazosin. Ciliary processes from animals after bilateral cervical ganglionectomy also show reduced cyclic AMP production at high concentrations of isoproterenol and this reduction is blocked by yohimbine, but not prazosin. This experiment suggests that the inhibition at high concentrations of isoproterenol is mediated by postsynaptic alpha 2-adrenergic receptors. Cyclic AMP production is relatively insensitive to epinephrine and norepinephrine, but their responses are potentiated by yohimbine. Catecholamines and clonidine, a specific alpha 2-adrenergic agonist, exhibit dose-dependent inhibition of forskolin-stimulated cyclic AMP production by ciliary processes. I50s from the dose-response curves are consistent with the characteristic binding affinities of these adrenergic agonists for alpha 2-adrenergic receptors: clonidine = epinephrine greater than norepinephrine greater than isoproterenol. Inhibition of forskolin-stimulated cyclic AMP production by clonidine is blocked by yohimbine but not by prazosin.(ABSTRACT TRUNCATED AT 250 WORDS)

Ophthalmic beta-blockers since timolol

In the twenty years since beta-blockers were proposed for treatment of glaucoma, use of topical timolol has increased to account for 70% of all glaucoma medications used. The objective of this article is to review the "newer" beta-blockers, and to address the generalization that "all ophthalmic beta-blockers are the same." The review concentrates on agents that have been studied as topical treatments for patients with elevated intraocular pressure. Sections on pharmacology and design of clinical trials are included to aid the ophthalmologist in evaluating the new drugs and published clinical reports. The major questions to consider in evaluating the therapeutic potential of a new beta-blocker for the treatment of glaucoma involve efficacy and safety: Is the drug as effective as timolol? Does it have a duration of action at least as long as timolol? Does it have ocular toxicity? Is it comfortable? What are its systemic effects?

Decreased intraocular pressure in the hypertensive human eye with betaxolol, a beta 1-adrenergic antagonist

In a double-masked randomized prospective study, 19 adult white subjects with primary open-angle glaucoma or ocular hypertension were treated twice daily with drops of 0.25% betaxolol (a relatively selective beta 1-adenoceptor antagonist) or placebo for six weeks. The nine betaxolol-treated subjects demonstrated a statistically significant average decrease in intraocular pressure of 3.8 +/- 5 mm Hg, evident after one week and persisting throughout the entire six-week treatment period. The ten placebo-treated subjects exhibited a statistically nonsignificant increase in intraocular pressure of 0.4 +/- 2.4 mm Hg. Mean systemic arterial blood pressure, pulse rate, corneal sensitivity, pupil diameter, and basal tear secretion remained unchanged in both groups. Transient stinging upon instillation of the eyedrops was the only side effect in the betaxolol-treated subjects but in no case did it necessitate cessation of therapy.

Time change of rabbit aqueous flow under influence of adrenergic drugs

The changes in the aqueous flow rate with time under action of acetazolamide, a selective alpha 1 agonist, phenylephrine, selective beta 2 agonist, salbutamol, and beta antagonist, timolol, were studied by the pre-invasive method of Johnson and Maurice in the normal rabbit. After intravenous injection of 50 mg kg-1 of acetazolamide, the experimental to control ratio of the apparent flow rate significantly decreased to 71 +/- 2% at 2 hr and 53 +/- 2% at 4 hr (mean +/- S.E.(M.), n = 7). After a single instillation of 5% L-phenylephrine, it showed two phase changes; it significantly increased to 121 +/- 5% at 1 hr and 110 +/- 3% at 2 hr, while it significantly decreased to 93 +/- 2% at 4 and 5 hr and 95 +/- 2% at 6 hr (n = 8). Pretreatment with prostaglandin biosynthesis inhibitor, flurbiprofen, did not cause significant effect on the phenylephrine action, while pretreatment with alpha antagonist, phenoxybenzamine abolished it. After a single instillation of 2.5% salbutamol, it significantly decreased to 78 +/- 4% at 1 hr, 84 +/- 3% at 2 hr and 91 +/- 3% at 3 and 4 hr (n = 8), while a single instillation of 0.5% L-timolol did not show significant effect on it. Pretreatment with timolol abolished the salbutamol action. The mean aqueous flow rate in the normal rabbit as determined by this method was 3.64 +/- 0.15 microliters min-1 (n = 20).

Stimulation of adenylate cyclase of ciliary processes in response to decreased inflow of aqueous humour

Intravitreal injection of ouabain was used to induce unilateral hypotony and to study the relationship of adenylate cyclase (AC) and sodium-potassium activated adenosine triphosphatase (NaK-ATPase) both of which are involved in the production of aqueous humour. After preliminary experiments, days 3 and 5 were chosen as representative times when IOP was maximally reduced and stable following ouabain injection. NaK-ATPase and adenylate cyclase activities were measured biochemically in the same homogenates of isolated ciliary processes (CP). Biochemical measurements showed that 46% of NaK-ATPase activity was inhibited after 3 days, and about 78% of NaK-ATPase was inhibited 5 days after ouabain injection. At the beginning of NaK-ATPase inhibition there was a significant stimulation of adenylate cyclase activity of the CP. The highest activities were seen 2 and 3 days after ouabain injection. The suggestion is made that these 2 enzymes are interdependent.

Regulation of aqueous flow by the adenylate cyclase receptor complex in the ciliary epithelium

The answer to how the beta-adrenergic receptor mediates a fall in intraocular pressure has been elusive. Methods of measurement have not been refined sufficiently. The separate changes after adrenergic treatment frequently are small, and the tissue effects are multiple. On a molecular basis, stimulation of the beta-adrenergic receptor activates intracellular adenylate cyclase to produce increased cyclic adenosine monophosphate. Acting by different cell-receptor mechanisms, but nonetheless potent, nonadrenergic stimulators of adenylate cyclase in the ciliary epithelium, such as cholera toxin and organic fluorides, have been studied in experimental animals. They reduce intraocular pressure by reducing net aqueous flow. When forskolin, a diterpene and potent stimulator of adenylate cyclase, became available, it was used in noninvasive topical form in the human eye to clarify the question of whether increased cyclic adenosine monophosphate reduces intraocular pressure and aqueous flow. Noninvasive studies in human eyes have demonstrated a 35% reduction in outflow pressure after the administration of forskolin in a 1% topical suspension, matched by a corresponding reduction in aqueous flow. Tonographic outflow facility was unaltered. Thus, the entire reduction in intraocular pressure can be accounted for by a reduction in net aqueous flow.

Inhibition of the epinephrine-induced reduction of intraocular pressure by systemic indomethacin in humans

In a prospective, randomized, double-masked study, 2% epinephrine applied topically twice each day for two weeks to the eyes of patients with glaucoma or ocular hypertension caused an 8.1 +/- 1.4-mm Hg (mean +/- S.E.M.) reduction of intraocular pressure in placebo-treated patients, but only a 1.9 +/- 0.6-mm Hg decrease in patients treated with 25 mg of orally administered indomethacin four times each day (P less than .0005). Systemic treatment with indomethacin for one week did not significantly increase intraocular pressure by itself (baseline, 19.7 +/- 0.6 mm Hg, vs 20.1 +/- 1.4 mm Hg after indomethacin treatment). When indomethacin treatment was discontinued in those patients receiving topical epinephrine, there was a further significant (P less than .05) reduction in intraocular pressure compared with the placebo-treated group. Since the ocular hypotensive effect of topically applied epinephrine is inhibited by indomethacin, a cyclo-oxygenase inhibitor, these results suggest that this reduction of intraocular pressure is at least partially mediated by the endogenous production of prostaglandins, or other cyclo-oxygenase products, and that the intraocular pressure of glaucoma patients undergoing epinephrine therapy may increase when systemic cyclo-oxygenase inhibitors such as indomethacin or aspirin are taken.

Aqueous flow in human eyes is reduced by forskolin, a potent adenylate cyclase activator

Forskolin, which lowers intraocular pressure in rabbits, monkeys, and human subjects, was tested for its effect on the rate of aqueous humor flow and on outflow facility. Topical sodium fluorescein was used to measure the rate of aqueous humor flow in forskolin or placebo treated eyes. Tonography was used to determine outflow facility before forskolin administration and at 3 hr after administration of the drug. In eight human subjects who showed reduction of intraocular pressure in response to a single drop of forskolin, flow was reduced by an average of 34%, compared to the contralateral eye during the same period of time. No significant change in outflow facility occurred. The action of forskolin in reducing intraocular pressure was the direct result of a reduction in net aqueous flow.

Effect of epinephrine in vitro on the morphology, phagocytosis, and mitotic activity of human trabecular endothelium

Epinephrine exerts a direct effect on cell morphology, phagocytosis and mitotic activity of human trabecular endothelium in primary culture. Its action is probably mediated through both beta and alpha adrenoceptors in a dose-time dependent manner. Younger cells and cells that were loosely attached to the substrate were found to be affected more rapidly and severely than were older cells and those in confluent regions where cell-to-cell attachment and stress fibers were well established. Continuous exposure to epinephrine at a concentration of 10(-5) M led to cessation of the normal cytokinetic cell movements, inhibition of mitotic and phagocytic activity, marked cell retraction, separation from the substrate, and, by 4-5 days, degeneration of cells. Similar, but less marked changes were seen with a concentration of 10(-6) M, the cell degeneration becoming apparent after one week of exposure. A still weaker concentration of epinephrine, 10(-7) M, did not result in cell degeneration even after 10 days of exposure and observation. On complete withdrawal of the drug, the cellular effects were reversible even after 3 days' exposure to 10(-5) M and 5-7 days' exposure to 10(-6) M epinephrine. The action of epinephrine was partially blocked by pretreatment of cultured trabecular cells with the beta-blocker, timolol. Available evidence suggests that the mechanism of action of epinephrine is mediated through both beta and alpha adrenoceptors, and that it intimately involves the cytoskeletal system of the cells. Extrapolation of our findings in vitro suggests that use of maximal doses of epinephrine over a prolonged time may contribute to tissue damage in certain conditions of glaucoma.

Ocular distribution of topically applied adrenaline in albino and pigmented rabbits

Systemic absorption, ocular distribution and ocular metabolism in albino and pigmented rabbit of topically applied 1% [3H]l-adrenaline eye drops was studied by liquid scintillation counting and thin layer chromatography. The effect of adrenaline on the pupillary diameter was also registered. The peak plasma level of adrenaline was reached at 150 min. The corneal adrenaline metabolism was substantial, but did not vary with the rabbit strain. At 30 min after instillation, the total adrenaline concentration of pigmented iris and ciliary body exceeded that of corresponding albino tissues. At 180 min the drug concentration of the iris and ciliary body did not differ between the rabbit strains. The time course of adrenaline induced mydriasis was equal in both rabbit strains. Since neither total adrenaline concentration at 180 min nor the time course of adrenaline induced mydriasis differed between the rabbit strains, the higher initial adrenaline uptake by pigmented tissues is not explained by pigment binding. It is proposed that the increased initial binding of adrenaline by pigmented tissues is caused by a difference between pigmented and albino tissues in the number of adrenergic neurones; this is also supported by the literature.

Effects of timolol on intraocular pressure following ocular adrenergic denervation

The effects of timolol on the elevation of intraocular pressure induced by orogastric water-loading were studied in conscious pigmented rabbits which had undergone unilateral, superior cervical ganglionectomy. Each rabbit was studied without timolol treatment and with unilateral 2% timolol treatment, either to the innervated eye or to the denervated eye, 90 min before water-loading. Timolol, applied to the innervated eye, significantly reduced the elevation of intraocular pressure in that eye, but not in the fellow eye. Timolol, applied to the denervated eye, did not affect the elevated intraocular pressure in either the denervated or the fellow eye. These results demonstrate that ocular adrenergic innervation participates in the mechanism of ocular hypotensive action of timolol in water-loaded pigmented rabbits.

The effect of timolol on the concentrations of albumin and IgG in the aqueous humor of the human eye

We investigated albumin and IgG concentrations in the aqueous humor of 41 patients before intracapsular cataract extraction (primary samples) and at the end of surgery (secondary samples). Albumin and IgG concentrations were determined in all samples by means of a quantitative fluoroimmunoassay. A short-term topical application of timolol in 24 eyes was associated with a significant increase in both proteins in the primary aqueous humor samples compared with 17 control samples (P less than .005). The ratios of albumin to IgG--even when corrected for serum levels--were not significantly different in the two groups. Timolol did not affect the change in these ratios in the secondary aqueous humor samples. Thus, we concluded that these findings were not caused by a breakdown of the blood-aqueous barrier, but rather resulted from reduced aqueous humor flow and undisturbed protein filtration.

Comparison of ocular hypotensive effects of 3 dosages of oral atenolol

Oral atenolol (25 mg twice daily and 50 mg and 100 mg once daily) and placebo were tested as additional therapy in a double-masked, randomised, cross-over study. Twenty-four patients (16 with chronic simple glaucoma and 6 with ocular hypertension) participated who had an intraocular pressure (IOP) higher than 21 mmHg. The mean fall of intraocular pressure varied between 28% and 36% and was observed 2 to 6 hours after administration. After 2 weeks of treatment there was still a small fall in intraocular pressure (13%) after 12 hours (for the 25 mg dose) and 24 hours (for the 50 mg and 100 mg dose), but this was not significant (p less than 0.5). There was a fall in blood pressure and reduced pulse rate which persisted for at least 30 hours. Some patients complained of tiredness during treatment periods. Oral atenolol may be useful additional therapy for glaucoma.