Ocular Hypotensive Activity Research Articles

Effects of Novel Ethacrynic Acid Derivatives on Human Trabecular Meshwork Cell Shape, Actin Cytoskeletal Organization, and Transcellular Fluid Flow

To determine efficacy and therapeutic index in the context of ocular hypotensive activity of the new ethacrynic acid (ECA) derivatives of the series (SA8,248 and SA8,389), 9,000 series (SA9,000, SA9,622 and SA9,995) and ticrynafen, we undertook a comparative evaluation of the dose-dependent effects of these compounds on human trabecular meshwork (HTM) cell shape, actin cytoskeletal organization, focal adhesions and transcellular fluid flow. Responses were either scored using an arbitrary scale of 1-5 or quantified. Compounds of the 9000 series (SA9,995>SA9,000>SA9,622) were found to be 14- to 20-fold more potent than ECA, ticrynafen or analogs from the 8,000 series (SA8,389>SA8,248) in terms of ability to induce cell shape alterations in HTM cells. Similarly, compounds of the 9,000 series (SA9,995>SA9,622>SA9,000) were found to be much stronger (2 to 20 fold) than ECA, ticrynafen or analogs of the 8000 series in terms of affecting decreases in actin stress fiber content in HTM cells. Analogs of the 9000 series (SA9,622>SA9,995>SA9,000) were also observed to be 8 to 10 fold more potent than ECA (SA8,389>ECA>SA8,248>ticrynafen) at eliciting decreases in cellular focal adhesions. Interestingly, analogs of the 9000 series (SA9,000>SA9,622>SA9,995) and SA8,248 demonstrated a huge increase (by many folds) in transcellular fluid flow of HTM cell monolayers as compared to ECA and ticrynafen. Collectively, these analyses revealed that the structural modification of ECA improves its ocular hypotensive efficacy, indicating that the SA9,000 series compounds might be promising novel ocular hypotensive drugs.

AL‐12182, a Novel 11‐Oxa Prostaglandin Analogue with Topical Ocular Hypotensive Activity in the Monkey.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mechanism of ocular hypotensive action of bimatoprost (Lumigan) in patients with ocular hypertension or glaucoma

Purpose To determine the mechanism of ocular hypotensive action of bimatoprost in patients with ocular hypertension or glaucoma. Design Double-masked, placebo-controlled, randomized, paired comparison crossover study of the effect of bimatoprost on aqueous humor dynamics. Participants and controls Twenty-nine patients with ocular hypertension or glaucoma. Methods Bimatoprost and a placebo were administered once a day, in the evening, for 7 days before assessment of aqueous dynamics using tonometry, Schiötz tonography, and fluorophotometry. Intraocular pressure (IOP) response to water drinking was measured. Main outcome measures Aqueous humor flow rate, outflow facility, and IOP. Results Intraocular pressure was lowered 29% in the morning and 33% at noon by bimatoprost. Aqueous humor flow was unchanged. Tonographic facility of outflow was increased 47% by bimatoprost relative to the placebo. Assuming an extraocular pressure of 8 mmHg and that extraocular pressure is not altered by bimatoprost, the calculated rate of pressure-insensitive outflow was increased 95% by bimatoprost. During the first hour after water drinking, bimatoprost dampened the IOP rise. Conclusion As was seen in healthy normal eyes, bimatoprost increased both the pressure-sensitive and the pressure-insensitive outflows of aqueous humor in patients with ocular hypertension or glaucoma. Bimatoprost had no significant effect on aqueous humor formation.

AL-12182, a novel 11-oxa prostaglandin analog with topical ocular hypotensive activity in the monkey

A series of 11-oxa prostaglandin analogs was evaluated for FP receptor binding and activation. Several compounds having aryloxy-terminated lower chains were found to be potent agonists. Topical ocular dosing of AL- 12182, the isopropyl ester prodrug of the potent agonist 13, lowered intraocular pressure in the monkey by 40% accompanied by minimal conjunctival hyperemia in the rabbit. AL- 12182 was synthesized on multigram scale starting with d-sorbitol.

New ethacrynic acid derivatives as potent cytoskeletal modulators in trabecular meshwork cells.

A series of ethacrynic acid (ECA) derivatives were synthesized and examined for ocular hypotensive activity. Efficacy was evaluated in a cell-shape assay, using human trabecular meshwork cells, and cytotoxicity in a (3-(4,5-dimethylthiazole-2-yl)-5-(3-carboxymethoxy phenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay, using cultured bovine trabecular meshwork cells. Many of the derivatives demonstrated efficacy equal to or greater than that of ECA. SA9000 was selected as the most promising candidate for a novel ocular hypotensive drug with few side effects.

A standardized approach for iris color determination.

Latanoprost, the phenyl-substituted prostaglandin F2alpha, has been found to be an effective agent for glaucoma therapy. This prostaglandin derivative exerts ocular hypotensive activity but is also associated with an untoward side effect, namely iris color changes. Latanoprost provoked iris color changes in cynomolgus monkeys and in multicenter clinical trials. Until now photographs were taken and compared with color plates to document these changes. The disadvantage of this method is obvious, i.e., the color luminance varies between measurements due to changes in the developer. Furthermore, subjective comparison of color changes relative to color plates rendered judgment subject to impression and opinion rather than to objective data. Therefore, a computerized method using a 3-CCD video camera attached to a slit lamp was developed. The signals were transferred to a computer and a single frame, which was "frozen" by means of a "grabber card." Camera and the computer had previously been calibrated and color plates were measured to check the standard conditions. They were evaluated by a software program displaying average color (as red, green, and blue values) of the selected area. This method provides a fast and accurate way to quantify color changes in the iris of both experimental animals and clinical trials.

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.

Effects of topical natural ergot alkaloids on intraocular pressure and aqueous humor dynamics in ocular normotensive rabbits.

Although it has been suggested that ergot derivatives may play a role in antiglaucoma therapy, little attention has been paid to the ocular hypotensive action of these drugs. Having previously reported in our laboratory that topical dihydroergocristine decreases intraocular pressure both in ocular normotensive and alpha-chymotrypsin-induced ocular hypertensive rabbits, the aim of the present work was to assess the effect of natural ergot alkaloids, ergocristine, alpha-ergocryptine and ergocornine, on the intraocular pressure and aqueous humor dynamics in ocular normotensive rabbits in order to further explore the ocular actions of these compounds. Intraocular pressure was measured with a pneumatonometer manometrically calibrated for the rabbit eye. Changes in tonographic facility of aqueous humor outflow and rate of aqueous humor inflow were evaluated in anesthetized rabbits. Natural ergot alkaloids were found to reduce intraocular pressure in ocular normotensive eyes in a dose-related fashion. These compounds decreased both tonographic outflow facility and, to a greater extent, aqueous humor inflow, which explains their final hypotensive effect.

Ocular hypotensive activity of prostaglandin F2 alpha (PGF2 alpha) analogs with neutral substituents at position 1 is predicted by the isolated cat iris sphincter smooth muscle preparation but not Ca+ signalling in Swiss 3T3 cells.

Typically, the C-1 carboxylic acid (CO2H) has been considered an essential pharmacophoric group for ligand binding to the FP-receptor. Historically, in drug design and development, a formal negatively charged carboxylic acid can be replaced with a group of similar pKa, such as tetrazole or an acyl sulfonamide. This change sometimes provides better selectivity and/or increased potency due to better metabolic stability. We investigated replacement of the C-1 carboxylic acid with a variety of uncharged C-1 substituents. A diverse series of Cl-analogs was synthesized and certain compounds, especially AGN-191129 (PGF2aOCH3), exhibited an apparent unique pharmacology, thus confiming the importance of the Cl-CO2H for binding to the FP-receptor.KeywordsIntraocular PressureRadioligand Binding StudyHuman RecombinantProstanoid ReceptorDiverse SeriesThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Design, in vitro stability, and ocular hypotensive activity of t-butalone chemical delivery systems

The objective of this work was to synthesize two bioreversible diacyl derivatives of t-butalone (chemical delivery systems), determine their chemical and in vitro stability, and investigate their potential use as topical antiglaucoma agents. The stability of these compounds was determined in isotonic phosphate buffers (pH range 5–8) and in selected biological media, including human whole blood, rabbit and rat blood, and the anterior segment tissues of rabbit. The ocular hypotensive activity of these compounds in unrestrained, normotensive albino rabbits was determined with a pneumatonometer. The two compounds were stable at lower pH. The stability decreased as the pH increased, suggesting their lability to base-catalyzed hydrolysis. These compounds exhibited significant differences in the hydrolytic rates in the whole blood among species examined (rat > rabbit > human). The observed rates of disappearance in different ocular tissues were indicative of relative enzyme activity in these media (iris-ciliary body > cornea > aqueous humor). The two compounds exhibited a significant ocular hypotensive activity (P < 0.01) at 2% dose level. The peak activity was found between 2 and 4 h, and the activity was maintained for 4.5 to 7 h. The dipivalyl derivative of t-butalone exhibited more pronounced decrease in intraocular pressure than that of diisovaleryl derivative. The present study suggests the possible use of diacyl derivatives of t-butalone as ocular hypotensive agents. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1026–1033, 2001

Mechanism of Action of Bimatoprost (Lumigan™)

Bimatoprost is a new ocular hypotensive agent that lowers intraocular pressure (IOP) in normal, ocular hypertensive, and glaucomatous eyes. Its mechanism of action has been studied in normal human subjects. Bimatoprost mildly stimulates the rate of aqueous humor flow during the day (13%) and at night (14%). Its ocular hypotensive action is due primarily to a 26% reduction in the tonographic resistance to outflow. Thus, bimatoprost enhances the pressure-sensitive outflow pathway. Additional beneficial effects may include an increase in the rate of flow via the pressure-insensitive outflow pathway (sometimes called the “uveoscleral outflow pathway”) and a lowering of the extraocular recipient pressure (sometimes called “episcleral venous pressure”). Reduction of tonographic resistance to aqueous humor outflow reduces steady-state IOP, an effect that is beneficial for the treatment of glaucoma. In addition to its effect on steady-state IOP, reduction of resistance allows the eye to recover more quickly from transient IOP elevations. The former effect is common to all ocular hypotensive drugs, but the latter effect is an exclusive property of drugs that reduce outflow resistance, such as bimatoprost.

Bimatoprost: a member of a new class of agents, the prostamides, for glaucoma management

Bimatoprost, a synthetic analogue of endogenous prostamides, is in development as a topical ocular hypotensive agent for the treatment of glaucoma and ocular hypertension. Prostamides are a newly discovered class of compounds that have been shown to have potent ocular hypotensive activity in the laboratory. Bimatoprost mimics the endogenous prostamides by lowering intraocular pressure (IOP). Bimatoprost provides outstanding control of IOP throughout the day, and a high percentage of patients receiving bimatoprost achieve the low target pressures important for clinical success. In controlled clinical trials, bimatoprost 0.03% given once daily has displayed efficacy superior to timolol 0.5% given twice daily, the current standard for therapy. Analysis of pooled six month data from two large Phase III trials demonstrated that mean IOP was consistently 2 - 3 mmHg lower with bimatoprost q.d. than with timolol b.i.d. Bimatoprost 0.03% q.d. has also been shown to provide significantly better diurnal IOP control than latanoprost 0.005% q.d., probably the most efficacious topical medication currently available. Patients receiving bimatoprost q.d. were more likely than timolol or latanoprost patients to achieve low target pressures. In all clinical evaluations, bimatoprost q.d. has been demonstrated to be safe and well-tolerated. Bimatoprost will likely be available for clinical use in 2001 and it has great potential to be superior to all other medications in IOP-lowering efficacy. It is anticipated that bimatoprost will have an important role in therapy for glaucoma and ocular hypertension.

Involvement of nitric oxide in the ocular hypotensive action of nipradilol

Purpose. To evaluate the role of nitric oxide (NO) in the mechanism of the ocular hypotensive action of nipradilol, a ß-blocker with a 1 -blocking activity. Methods. Change in intraocular pressure (IOP) of albino rabbits was measured after a single application of carboxy-PTIO (c-PTIO), an NO trapping agent. Next, IOP change was measured every hour for 5 hours after the instillation of 0.25% nipradilol into one of the eyes with and without c-PTIO pretreatment of both eyes. IOP change induced by desnitro-nipradilol was also examined. The outflow facility and uveoscleral outflow were determined by two-level constant pressure and anterior chamber perfusion methods before and at 3 hours after the application of nipradilol with and without c-PTIO pretreatment. Results. Topical administration of c-PTIO showed no significant effect on IOP. Unilateral instillation of nipradilol reduced IOP significantly compared with control eyes with a maximum reduction of 3.6 mmHg and effect duration of 3 hours. Pretreatment with c-PTIO partially inhibited the reduction during an earlier period (1~2 hours) and completely at 3 hours. IOP change by desnitro-nipradilol was similar to that by nipradilol with c-PTIO pretreatment. Nipradilol increased both outflow facility and uveoscleral outflow at 3 hours, whereas pretreatment with c-PTIO inhibited both of these outflows. Conclusions. Results indicate that ocular hypotensive action by nipradilol during the relatively late period may be mainly due to enhancement of aqueous humor outflow by NO at least in the rabbits.

Intraocular Pressure-Lowering Activity and In Vivo Disposition of Dipivalyl Terbutalone in Rabbits

The ocular hypotensive activity and in vivo disposition of dipivalyl terbutalone, a chemical delivery system for terbutaline, were investigated in the albino rabbit model. The dose–response relationship was assessed at drug concentrations ranging from 0.5 to 4% in normal saline. Intraocular pressure (IOP)-lowering activity of dipivalyl terbutalone was compared with epinephrine in equal concentrations. The in vivo disposition was investigated after topical administration of dipivalyl terbutalone at 4% dose level for which two metabolic products, terbutaline, and terbutalone, were monitored in different anterior segment tissues/fluid of albino rabbits, including corneal and iris–ciliary body homogenates and aqueous humor. The instillation of 0.5, 1, 2, and 4% solutions (1 drop of 50 μL) significantly decreased the IOP of normotensive rabbits in a dose-dependant manner. At the highest dose, the maximum reduction (5.6 ± 0.65 mm Hg) was observed at 3 h. In a comparative efficacy study, dipivalyl terbutalone was found to be more effective than epinephrine. In the in vivo distribution after the topical administration of dipivalyl terbutalone, terbutaline was found only in the iris–ciliary body, whereas terbutalone was found in all parts of the eye studied. This work suggests the potential use of dipivalyl terbutalone as an antiglaucoma agent, representing a new chemical delivery system for terbutaline.

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.

Ocular hypotensive activity of prostaglandin F 2α (PGF 2α) analogs with neutral substituents at position 1 is predicted by the elated cat iris sphincter smooth muscle preparation but not Ca 2+ signaling in Swiss 3T3 cells

Ocular hypotensive activity of prostaglandin F 2α (PGF 2α) analogs with neutral substituents at position 1 is predicted by the elated cat iris sphincter smooth muscle preparation but not Ca 2+ signaling in Swiss 3T3 cells

Ocular hypotensive, vasorelaxant and cyclic AMP intermediation activities of clozapine displaying antiglaucoma properties

Clozapine, an atypical antipsychotic agent with multiple receptor antagonist activities, was investigated in vivo and in vitro to discover its effects on intraocular pressure and blood flow, on the contractility of ciliary muscle and nonophthalmologic blood vessels, on calcium concentration in A7r5 smooth muscle cells, and on cyclic AMP intermediation. The adrenergic and muscarinic mechanisms involved in the above effects were also examined. In rabbits, clozapine (0.1, 0.25, and 0.5%) prolonged (IOP) recovery time and inhibited IOP response. Clozapine (0.1 and 0.25%) also produced a significant increase in ocular blood flow in this iris, ciliary, retina, and choroid at 30 to 180 min after drug administration. In isolated guinea pig thoracic aorta, clozapine relaxed phenylephrine (10 μM)- and KCl (75 mM)-induced contractions, the estimated IC50 values being 20.4 ± 3.1 nM and 10.6 ± 1.8 μM, respectively. Clozapine (0.1–100 μM) inhibited phenylephrine (10 μM)-induced influx of Ca2+, the estimated IC50 value being 0.4 ± 0.1 nM. In isolated pig eye ciliary muscles, clozapine (1.0–100 μM) inhibited carbachol (10 μM)-induced contractions, the estimated IC50 value being 5.8 ± 1.2 μM. Clozapine (0.1–100 μM) increased cyclic AMP accumulation in pig's ciliary bodies, including ciliary process, ciliary muscle, and trabecular meshwork. Pretreatment with carbachol (100 μM) first decreased, then increased, clozapine-induced cyclic AMP accumulation. Studies of pretreatments with various muscarinic receptor antagonists at 100 μM revealed that pirenzepine significantly enhanced clozapine (100 μM)-induced cyclic AMP accumulations in trabecular meshwork, while 4-DAMP methiodide inhibited it in ciliary bodies, and methoctramine decreased it in ciliary process. The ocular hypotensive effects of clozapine may be mostly related to its muscarinic agonist/antagonist activities and associated cyclic AMP increasing activities, which lead to ciliary muscle relaxation and a possibly associated increase in uveoscleral outflow. Clozapine's ability to increase blood flow and relax vessels may be attributed to its ability to block α-adrenergic and decrease intracellular calcium. IOP is considered the major cause of glaucoma, and compounds which are capable of reducing IOP are considered useful for glaucoma treatment. Based on the results above, clozapine may potentially be important in the development of new antiglaucoma agents. Drug Dev. Res. 44:163–173, 1998. © 1998 Wiley-Liss, Inc.

Prostaglandin Effects on the Contractility of Bovine Trabecular Meshwork and Ciliary Muscle

The ocular hypotensive activity of prostaglandins (PGs) has previously been demonstrated in various species including man. The underlying mechanism of action of prostanoids other than PGF2αremains contentious. Because the trabecular meshwork and ciliary muscle are believed to have a role in the regulation of aqueous humor outflow, the aim of this study was to identify the PG-receptor subtypes present in these tissues using receptor-selective agonists. Contractions of isolated strips of bovine trabecular meshwork and ciliary muscle were recorded isometrically in continuously perfused tissue chambers. Contractile activity of PGs was determined relative to a maximally effective concentration of carbachol (1 μM) as a standard agonist. The following prostanoids were employed: PGF2α, 17-phenyl PGF2α(FP-receptor agonists), sulprostone (EP3>EP1-agonist), AH13205 (EP2-agonist), 11-deoxy PGE1(non-selective EP-agonist), and U-46619 (TP-agonist). The thromboxane-mimetic U-46619 elicited a strong contraction of the trabecular meshwork with the highest concentration (1 μM) being almost twice as efficacious (186.6%) as the maximal carbachol concentration, whereas the effect on the ciliary muscle was small. The U-46619 induced trabecular meshwork contraction could be blocked with a potent and selective TP-receptor antagonist, 1 μMSQ29548, indicating the involvement of TP-receptors. The other PG-analogs studied had either no or a small but statistically significant effect. Thus, 17-phenyl PGF2α(1 μM) weakly contracted the ciliary muscle (4.8%), sulprostone (1 μM) the trabecular meshwork (10.1%). 11-deoxy PGE1(1 μM) and AH13205 (10 μM) elicited relaxations in both tissues precontracted with carbachol (1 μM). The relaxant effects were more pronounced in trabecular meshwork (15.6% for 11-deoxy PGE1and 21.4% for AH13205) than ciliary muscle (6.8 and 7.4% respectively). PGF2αdid not elicit a significant response in either tissue. Our studies suggest the existence of TP- and EP2-receptors in the bovine trabecular meshwork and potentially FP- and EP2-receptors in the ciliary muscle. In conclusion, thromboxane-mimetics and EP2-agonists have opposing activities on contractile elements in the meshwork and may modulate trabecular outflow in a functionally antagonistic manner. Prostanoid effects on ciliary muscle appear rather modest compared to parasympathomimetic drugs. It is conceivable that TP-agonists may substantially affect trabecular outflow.

Vanidilol: a vanilloid-type vasorelaxant and ocular hypotensive beta-adrenoceptor blocker with partial beta-2-agonist activity.

Vanidilol, [4'-(2-hydroxy-3-(tert-butylamino)propoxy)-3'-methoxyphenyl] -benzaldehyde, newly synthesized from vanillin, is a vanilloid-type beta-adrenoceptor blocker. The beta-adrenoceptor-blocking properties of vanidilol were studied both in vivo and in vitro. Intravenous injection of vanidilol (1.0, 3.0, 5.0 mg/kg) in anesthetized Wistar rats produced a decrease in blood pressure and a dose-dependent bradycardia response. Vanidilol inhibited the tachycardia effects induced by (-)isoproterenol, but had no blocking effect on the arterial pressor responses induced by phenylephrine. In isolated guinea-pig tissues, vanidilol attenuated the (-)isoproterenol-induced positive chronotropic and inotropic effects of the atria and trachea relaxation responses in a concentration-dependent manner. The parallel shift to the right of the concentration-response curve of (-)isoproterenol suggested that the agent was a beta-adrenoceptor competitive antagonist. The apparent pA2 values for vanidilol on the right atria, left atria and trachea were 7.67 +/- 0.03, 7.89 +/- 1.02 and 7.66 +/- 0.15, respectively, denoting that vanidilol was a nonselective beta-blocker. The intrinsic sympathomimetic activity of vanidilol and propranolol was determined on isolated atria and trachea from reserpinized guinea pigs. Propranolol caused significantly negative inotropic and chronotropic effects at 10(-6) mol/l or above, whereas vanidilol possessed less cardiodepressant activities than propranolol. In reserpinized tracheal strips, vanidilol produced dose-dependent relaxant responses, but propranolol was ineffective. Preincubating the preparations with ICI 118,551 (0.1-10 nmol/l), a beta 2-adrenoceptor antagonist, significantly shifted the concentration-relaxation curves of vanidilol to a region of higher concentrations. In isolated guinea-pig thoracic aorta, vanidilol (0.1-10 mumol/l) inhibited the phenylephrine (10(-5) mol/l)-induced tonic contraction in vascular smooth muscle which was related to the block of calcium influx. In 20% saline-perfused rabbits, vanidilol showed a marked delay in intraocular pressure recovery, demonstrating an ocular hypotensive action. Binding characteristics of vanidilol and propranolol were evaluated in [3H]dihydroalprenolol binding to porcine ventricular membranes. Vanidilol was less potent than propranolol in competing for the beta-adrenoceptor-binding sites. On the other hand, vanidilol had a high hydrophilicity in comparison with propranolol. In conclusion, vanidilol exhibited nonselective beta-adrenoceptor blocking, vasorelaxant and ocular hypotensive activities, but was devoid of alpha-adrenoceptor blocking and beta 1-agonist activity. Partial beta 2-adrenoceptor agonist activity and inhibitory activity on calcium influx may share in the vasorelaxant activity.

Computer-assisted evaluation of iris colour changes in primate toxicity studies

Iris colorimetry was required for a 52-week primate toxicity study with topical administration of eye drops with ocular hypotensive activity in order to evaluate possible color changes in the Cynomolgus monkey. The conventional method for color determination is based on the comparison of the object with a standard color scale. To ensure GLPcompliant documentation, photographs have to be taken and archived. Development of the photographs over a 6-months period creates the problem that due to changes in the developer, each photograph must be developed manually and calibrated to a color scale which must be included on the photograph along with the object. This method is expensive, complicated, time constiming and unreliable. Therefore, we decided to develop a computerized method (patent pending). A 3-CCD (3 chip) video camera is attached to a slit lamp. The signals are transferred to a computer and a single frame depicting one eye from the front—is “frozen” by means of a “grabber card”. The computer and the light source of the slit lamp are calibrated in advance. The picture of the iris is evaluated using an image analysis software package. The program displays the average color as numerical RGB (red, green, blue)-values. The pictures are stored as raw data on optical disc. This method provides a fast and accurate means of measuring color changes in the iris of experimental animals. It can also be applied as standardized method in humans.