Effects of selective dopamine-1 receptor activation on intraocular pressure in man

Effect of Oral Captopril (SQ 14225) on Intraocular Pressure in Man

The effects of the angiotensin converting enzyme (ACE) inhibitor captopril (SQ 14225) on intraocular pressure (IOP) were studied. Four groups were analyzed: group A, ten control subjects; group B, ten hypertensive patients with normal IOP; group C, ten normotensive patients with primary open angle glaucoma (POAG); and group D, ten hypertensive patients with POAG. Systolic and diastolic blood pressure, heart rate, pupil diameter, IOP and total outflow facility were recorded at baseline and at 1-h intervals up to 3h after an oral dose of 25 mg captopril or placebo, given in a randomized, double-blind cross-over fashion. The alternative treatment was given a week later. Captopril significantly lowered IOP in all patients, with no effects on heart rate and pupil diameter. Blood pressure changed only in patients with hypertension (groups B and D). Total outflow facility, measured by conventional tonography, increased significantly in all groups. These findings indicate that oral captopril could represent a new antiglaucomatous compound.

Role of dopaminergic receptors in glaucomatous disease modulation

Both studies on animals and humans suggest the presence of dopamine (DA) receptors in the anterior segment of the eye. Their role in the dynamics of intraocular pressure (IOP) is not yet clear. DA₂ and DA₃ receptors are mainly located on postganglionic sympathetic nerve endings. Their stimulation reduces the release of norepinephrine and suppresses the production of aqueous humor. DA₁ receptors seem to be more expressed by the ciliary body and the outflow pathway of aqueous humor. The administration of DA₁-selective agonists stimulates the production of aqueous humor, increasing IOP, whereas DA₂- and DA₃-selective agonists could reduce IOP and, therefore, the risk to develop a glaucoma (GL). GL is a broad spectrum of eye diseases which have in common the damage to the optic nerve and the progressive loss of the visual field. Further studies are desirable to clarify the role of the dopaminergic system and the usefulness of DA₂ and DA₃ agonists in reducing IOP.

Determination of dopamine D1 receptors in the human uveo scleral tissue by light microscope autoradiography

The aim of this paper is to clarify the distribution of Dopamine D1 (DA D1) receptors in the uveo-scleral tissue of human eyes with or without elevated intraocular pressure (IOP) and to study the relationships between DA D1 receptors and uveo-scleral tissue. Samples of human uveo-scleral tissue were taken from seven men undergoing eye surgery for a traumatic lesion of the anterior segment of the eye, without involvement of the iris-corneal angle and /or from eye donors. The subjects (in whom one eye bulb had been surgically enucleated) had been previously enrolled in our medical protocols because they suffered for increased IOP, while the eye donors (of both eye bulbs) had a normal IOP. Frozen sections from the uveo-scleral tissue were submitted to biochemical characterization and to morphological autoradiographic techniques for detection of DA-D1 receptors. [3H]-SCH-23390 was used as a ligand of Dopamine D1 receptors. [3H]-SCH 23390 was bound by sections of the human uveo-scleral tissue. The pharmacological profile of the binding was consistent with the labeling of D1 receptors. Light microscope analysis was used for localization of D1 receptors and revealed an accumulation of the radioligand in the human uveo-scleral tissue. In eyes with normal IOP there is a high reaction. The Bmax of radioligand decreases in the eyes with increased IOP. The possibility that dopaminergic receptors play a role in the controlling uveo-scleral tissue functions is suggested.

Effect of oral losartan potassium administration on intraocular pressure in normotensive and glaucomatous human subjects

The effects of the type 1 angiotensin II receptor antagonist Losartan potassium on intraocular pressure (IOP) were studied. Four groups of subjects were analysed: group A, ten controls; group B, ten patients with essential arterial hypertension and with IOP within the normal range; group C, ten patients with primary open angle glaucoma (POAG), but without essential arterial hypertension; group D, ten patients with arterial hypertension and POAG. The study design was held in a randomized crossover double-blind fashion. Systolic and diastolic arterial pressure, heart rate, pupil diameter, IOP and total outflow facility were recorded at baseline and at 1 hr intervals up to 6 hr, following the oral administration of 50 mg of Losartan potassium and/or placebo. The alternative treatment was given a week later. Drug administration significantly reduced IOP in all subjects. No variation in heart rate and pupil diameter was observed during the follow-up period. Blood pressure dropped only in arterial hypertensive patients (groups B and D). Total outflow facility increased significantly in all groups. Placebo did not induce any variation in all groups. These findings demonstrate that the mechanism by which Losartan potassium reduces intraocular pressure is not mediated by a decrease in blood pressure, but rather it is more specific, confirming the role of the renin-angiotensin system also in the regulation of intraocular pressure in man.

Fenoldopam, a selective dopamine-1 receptor agonist, raises intraocular pressure in males with normal intraocular pressure

Recent studies have suggested that intravenous infusion of fenoldopam, a selective dopamine-1 receptor agonist, elevates intraocular pressure (IOP) in man. This study evaluated the effect of intravenous fenoldopam on IOP, aqueous humor outflow facility and gonioscopy in 12 healthy human subjects. Three doses (0.2, 0.5 and 1.0 microg/kg/min) were infused for 120 minutes in a double masked, placebo controlled, four-way crossover design. IOP was measured every 20 minutes in the supine position and every 40 minutes while sitting during the drug and placebo infusions. Tonography and gonioscopy were performed at baseline and after 120 minutes of infusion. Compared to placebo, IOP increased by 3.5 mm Hg (32%) for the lowest dose, 5.8 mm Hg (46%) for the intermediate dose, and 6.9 mm Hg (55%) for the highest dose (p<0.05 for all three doses). IOP returned to baseline within 30 minutes of stopping the infusion. The outflow facility decreased from baseline by 26% after 120 minutes of infusion for all drug doses. In contrast, outflow facility increased from baseline by 11% during placebo infusion. Compared to placebo, the fenoldopam induced changes in outflow were statistically significant (p<0.05). There was no change in the gonioscopic appearance of the anterior chamber angle during the infusion. This study shows that systemic administration of a selective dopamine-1 receptor agonist causes a significant dose-dependent increase in IOP that can be explained in part by diminished outflow facility. These results support a role for the dopamine-1 receptor in the modulation of IOP in general and suggest modulation of aqueous humor outflow by dopaminergic receptors.

Fenoldopam: a new dopamine agonist for the treatment of hypertensive urgencies and emergencies

Fenoldopam is a selective dopamine agonist that is being considered for the parenteral treatment of systemic hypertension. In both an oral and parenteral form, the drug causes peripheral vasodilation by stimulating dopamine-1 adrenergic receptors. Its pharmaco-dynamics are reviewed in this article, along with the clinical experiences in patients with hypertensive urgencies and emergencies. Intravenous fenoldopam may provide advantages over sodium nitroprusside because it can induce both a diuresis and natriuresis, is not light sensitive, and is not associated with cyanide toxicity. There is no evidence for rebound hypertension after discontinuation of fenoldopam influsion.

Fenoldopam: a review of its pharmacodynamic and pharmacokinetic properties and intravenous clinical potential in the management of hypertensive urgencies and emergencies

Fenoldopam is a dopamine agonist that causes peripheral vasodilation via stimulation of dopamine 1 (D1) receptors. The efficacy of an intravenous infusion of fenoldopam in decreasing blood pressure in patients with a hypertensive urgency, including patients who developed hypertension after coronary artery bypass graft surgery, and in a small number of patients with hypertensive emergency, is similar to that of sodium nitroprusside. However, unlike sodium nitroprusside, fenoldopam also increases renal blood flow and causes diuresis and natriuresis. There is no evidence of rebound hypertension after stopping the infusion. As the tolerability profile of fenoldopam is generally similar to that of sodium nitroprusside, fenoldopam appears to be an effective alternative to sodium nitroprusside in the immediate treatment of patients who develop severe hypertension and in whom oral treatment is not practical. Fenoldopam may be particularly useful in patients who develop hypertension after coronary artery bypass graft surgery, but further studies are required to confirm its role in hypertensive emergency.

Effect of intravenous fenoldopam on intraocular pressure in ocular hypertension

Intravenous fenoldopam, a selective dopamine-1 receptor agonist, was compared with placebo in this randomized, double-blind, two-period crossover study to evaluate its effects on intraocular pressure, aqueous dynamics, and macular blood flow in patients with elevated intraocular pressure or primary open-angle glaucoma. Doses of fenoldopam were titrated up to a maximum of 0.5 microgram/kg/min. Intraocular pressure, measured by pneumotonometry, was the primary outcome variable. Other outcomes included macular blood flow assessed by blue field examination, visual field examined by automated perimetry, aqueous outflow facility measured by tonography, and aqueous humor production determined by fluorophotometry. During infusions of fenoldopam, intraocular pressure increased from a mean baseline level of 29.2 mmHg to a mean maximum level of 35.7 mmHg. During the placebo infusions, pressure increased from a mean baseline of 28.4 mmHg to a mean of 29.0 mmHg at the time point that corresponded to the mean maximum intraocular pressure on the day intravenous fenoldopam was administered, to yield a mean difference in pressure between study days of 6.7 mmHg (P < 0.05). There were no apparent changes in macular blood flow, visual fields, or production or outflow of aqueous humor associated with fenoldopam infusion. The increase in intraocular pressure seen in this population of patients with ocular hypertension during infusions of fenoldopam is consistent with fenoldopam-associated increases in intraocular pressure reported in previous studies of healthy volunteers and of patients with accelerated systemic hypertension. These results further suggest that dopamine-1 receptors play a role in the regulation of intraocular pressure.

Ocular hypotensive effect of topical ketanserin in timolol users

BACKGROUND

Ketanserin is a specific antagonist of 5-HT2 and 5-HT1c receptors. These receptors are linked to the stimulation of phosphoinositide metabolism and are involved in IOP controls. Orally and topically administered ketanserin reduces IOP in normotensive and glaucomatous eyes.

METHODS

Ketanserin 0.5% eye drops were administered to 20 patients with primary open-angle glaucoma in a randomised, crossover, double-masked fashion to evaluate the effect of ketanserin in glaucomatous patients already receiving timolol who did not have controlled IOP (> 21 mmHg). Mean and range of IOP curve (8.00 a.m.-8.00 p.m.), pupil diameter, Schirmer I, basal secretion test and BUT values were recorded at baseline and after 2 weeks of topical administration of ketanserin or placebo twice daily. The alternative treatment was given 2 weeks later and the same protocol was repeated.

RESULTS

When patients received placebo no significant variations were found in the analysed parameters. Ketanserin significantly reduced mean IOP (19.5%) and was effective for up to 12 h without inducing variations of tear secretion or pupil diameter. No systemic side effects were observed, and no significant variations in ocular symptoms and signs were reported.

CONCLUSION

These results indicate that topical administration of ketanserin may be useful to reduce IOP in patients not controlled with beta-blockers.

Effects of dopamine D-1 and D-2 receptors on intraocular pressure in conscious rabbits

This investigation was designed as a randomized, placebo-controlled, double-masked, crossover study in NZW rabbits with normal intraocular pressure (IOP) to investigate dopaminergic effects on IOP. SKF 38393, a selective D1-receptor agonist, increased, and SDZ PSD-958, a selective D1-receptor antagonist, decreased IOP, respectively. The selective D2-receptor agonist quinpirole decreased IOP, whereas the selective D2 receptor antagonist metoclopramide had no significant effect. Combinations of quinpirole with SDZ PSD-958 decreased IOP in an additive manner. SDZ GLC-756, a mixed D1-receptor antagonist/D2-receptor agonist, decreased IOP in a dose-dependent manner with a maximum effect greater than the maximum effects produced either by the D1-receptor antagonist SDZ PSD-958 and the D2-receptor agonist quinpirole. The effect of SDZ GLC-756 could only be partially blocked by the selective D2-receptor antagonist metoclopramide suggesting that both D1-receptor blockade and D2-receptor stimulation participate in its IOP-lowering effect. Tonography suggests that SDZ GLC-756 has no significant effect on outflow facility. Furthermore, the results suggest that both D1 and D2 receptors each play an independent role in the regulation of IOP in rabbits. Thus, simultaneous blockade of D1 receptors and stimulation of D2 receptors may provide a new pharmacological approach for the treatment of ocular hypertension frequently associated with glaucoma.

The novel dopamine D-1 antagonist and D-2 agonist, SDZ GLC-756, lowers intraocular pressure in healthy human volunteers and in patients with glaucoma

PURPOSE

To investigate the intraocular pressure (IOP)-reducing effect and side effects of SDZ GLC-756, a novel dopamine D-1 antagonist and D-2 agonist, in control subjects and patients with open-angle glaucoma or ocular hypertension.

METHODS

A single-application, randomized, placebo-controlled, double-masked study was performed. SDZ GLC-756 eye drops at a concentration of 0.01% (n = 6) or 0.1% (n = 6) were administered to one eye in control subjects, vehicle alone (control) to the contralateral eye. In glaucoma patients the trial was designed as a crossover study administering SDZ GLC-756 (0.1%) eye drops and vehicle alone (control) to one eye in 12 patients with open-angle glaucoma or ocular hypertension.

RESULTS

In control subjects, IOP decreased significantly by 2.0 +/- 0.4 mmHg (P < 0.01) after treatment with 0.01% SDZ GLC-756 and by 4.7 +/- 0.5 mmHg (P < 0.001) after treatment with 0.1% SDZ GLC-756. In the glaucoma group, IOP decreased by 6.8 +/- 0.6 mmHg (P < 0.001) (range, 4-11 mmHg). In both groups, treatment with 0.1% eye drops resulted in a significant IOP-lowering effect for 6 hours, and for 3 hours with treatment with 0.01% eye drops. A significant IOP-lowering effect (P < 0.05) also was found in the contralateral eye. Except for slight conjunctival hyperemia lasting up to 30 minutes after drug application, no ocular or systemic side effects were observed.

CONCLUSION

SDZ GLC-756 reduced IOP significantly for approximately 6 hours. However, due to the study design with repeated IOP measurements before drug administration, the clinical efficacy of the preparation used remains unclear. The only systemic or local side effect observed was slight conjunctival hyperemia. The simultaneous D-1 antagonistic and D-2 agonistic properties of SDZ GLC-756 may provide a new pharmacologic approach to treating glaucoma and ocular hypertension, which deserves further investigation.

Effect of topical ketanserin administration on intraocular pressure

The effect of topical ketanserin on intraocular pressure (IOP) in normotensive and hypertensive eyes was evaluated. The study was performed on 10 healthy volunteers and 10 glaucomatous patients. Systolic arterial blood pressure (SBP), diastolic arterial blood pressure (DBP), heart rate (HR), IOP, tonographic outflow facility, pupil diameter, corneal thickness, and tear secretion were recorded at baseline and at 1 hour intervals for 12 hours after topical administration of 0.5% ketanserin or placebo, given in a randomised, double masked, crossover fashion. The alternative treatment was given 1 week later. In all subjects ketanserin significantly lowered IOP, while no variations in SBP, DBP, HR, pupil diameter, corneal thickness, and tear secretion were found. When subjects received placebo no significant variations of IOP occurred. Total outflow facility, measured by conventional tonography, increased significantly after drug administration in all subjects. Ketanserin is effective up to 6 hours in control subjects and 9 hours in glaucomatous patients. The placebo did not induce any change in this component of the aqueous humour dynamic in normal or in glaucomatous eyes. The findings indicate that topical ketanserin might be added to the list of antiglaucomatous agents.

Biphasic dose-dependent effects of dopamine and involvement of dopamine autoreceptors on intra-ocular pressure in the rabbit

1. This work was conducted to provide new data concerning the possible dose-dependent activity of dopamine (DA) after ocular instillation. Experiments were done in rabbits with normal intraocular pressure (IOP), or after transitory induced ocular hypertension in water-loaded animals. 2. In ocular normotensive animals, a biphasic dose-dependent activity is observed, with no significant effect for 0.001% and 0.003% DA, a decrease in IOP after 0.005% and 0.01% DA instillation, then an important increase in IOP at concentrations from 0.05% onwards. 3. During transitory ocular hypertension, this phenomenon was confirmed, with a marked ocular hypotensive activity for 0.01% DA, no effect after 0.005% DA, then an important ocular hypertension with 0.05% and 0.5% DA as compared to the control group (0.9% NaCl). 4. An immediate and similar ocular hypertensive effect with DA could be reproduced by a subsequent instillation at high concentration (1%), while the hypotensive activity induced at low concentration (0.01%) is followed by a long-lasting refractory period (about 18 h). 5. Such a dose-dependent biphasic effect was also observed with N-methyl-dopamine (NMDA) after ocular instillation. The effects of instilled dopaminergic compounds were tested and ocular hypotensive activities of the S(-)enantiomer of the DA analogues 3-(3-hydroxyphenyl)-N-propylpiperidine (3-PPP), and of thiothixene (TIX) were also demonstrated. 6. The possible relationships to DA1 and DA2 receptors of the dual effect is discussed.

Dopamine, dopaminergic drugs and ocular hypertension

The study refers to the clinical experiences performed with several D1 and D2 dopaminergic receptors agonists in 20 patients with high tension open angle glaucoma. The substances were administered topically as eye drops as well as an ocular eye bath. The parameter examined was intraocular pressure (IOP). The substances taken in consideration were: Dopamine, Ibopamine (dopamine analog), Fenoldopam and 3B90 (D1-receptor agonists) and Bromocriptine (dopaminergic agonist with higher affinity for D2 than for D1-receptors). It has been shown that all selective D1-receptors agonists induce a significant increase in IOP only in eyes with hydrodynamic disorders (p < 0.001). Such hypertensive effects could not be antagonized either by topically administered dopaminergic antagonists (Sulpiride, D2-receptors antagonist, and Haloperidol, non-selective dopaminergic antagonist) or by the pretreatment with the commonly used topical antiglaucomatous drugs. The only substance which proved able to inhibit the IOP increase induced by the D1-receptors agonists was the D1-selective antagonist SCH-23390, suggesting that IOP increase may be a result of a stimulation of the D1-receptors. The authors hypothesize that dopaminergic system may play a role in the regulation of aqueous humor hydrodynamics.

Effect of oral ketanserin administration on intraocular pressure in glaucomatous patients

We evaluated the effect of the antihypertensive drug ketanserin, a 5-HT antagonist, on intraocular pressure (IOP) in 20 patients with ocular hypertension. IOP, pupil diameter, systolic arterial pressure (SBP), diastolic arterial pressure (DBP) and heart rate (HR) were recorded at baseline and at 1-hr intervals for 3 hr after oral administration of 20 mg ketanserin or placebo, given in a randomized, double masked, cross-over fashion. The alternative treatment was given a week later. In all patients, ketanserin significantly lowered IOP and SBP, while no variations in pupil diameter, DBP and HR were found. Moreover, after drug administration, total outflow facility, measured by conventional tonography, increased significantly. These findings indicate that oral ketanserin could represent a new antiglaucomatous drug.

Biochemical and functional evidence for the presence of dopamine D1 receptors in the bovine ciliary body

The present paper reports both functional and biochemical evidence for the presence of dopamine D1 receptors in the bovine ciliary body. Dopamine (DA) and dopamine D1 agonists (such as SKF 38,393) but not D2 agonists (such as LY 141,865) produced a concentration-related decrease in the tone induced by a maximally active concentration of carbachol (1 x 10(-4)-5 x 10(-4) M). The maximal relaxation obtained was 100% of the carbachol response using 10(-5) M dopamine or 5 x 10(-6) M SKF 38,393. SCH 23,390, a D1 antagonist, but not (-)-sulpiride, antagonized the effect of DA and SKF 38,393. In accordance with the functional data, radioreceptor binding experiments revealed the existence of a high affinity saturable [3H]SCH 23,390 binding to membranes prepared from ciliary body (Bmax: 344 fmol mg protein-1; Kd: 0.87 nM). The binding was specifically displaced by SCH 23,390, dopamine and dopamine D1 agonists, but not by norepinephrine, D2 agonists, or antagonists such as LY 141,865 and sulpiride. No specific binding was found when using dopamine D2 ligands, such as tritiated spiroperidol.