Hypotensive effect of bromocriptine in normal eyes

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.

Ocular inhibitory effects of the dopamine DA2 agonist (Ha-118) in cats and rabbits

1. Topical administration of the dopamine (DA2) receptor agonist, Ha-118, produced unilateral ocular hypotension and miosis in normal cats. 2. The ocular hypotensive and mitotic effects of Ha-118 were not observed in surgically sympathectomized cats indicating that an intact sympathetic pathway is necessary to demonstrate activity. 3. Ha-118 caused dose-dependent suppression of contractions of the cat nictitating membrane (CNM) elicited by electrical stimulation of the pre- and postganglionic sympathetic nerve trunks but not by exogenously administered noradrenaline suggesting that Ha-118 affected prejunctional but not ganglionic or postjunctional receptors. 4. Sulpiride antagonized Ha-118-induced inhibition of neuronally mediated contractions in the CNM suggesting an interaction at DA2 receptors. 5. Topical administration of Ha-118 inhibited the rise in intraocular pressure induced by oral water loading in rabbits. 6. Topical pretreatment with metoclopramide, a DA2 antagonist, inhibited the ocular antihypertensive effect of Ha-118 in rabbits. 7. These studies demonstrate that Ha-118 decreased intraocular pressure (IOP) and pupil diameter (PD) in the cat and that this activity can be correlated with suppression of peripheral sympathetic tone in the CNM.

Antagonism by domperidone of the ocular hypotensive effect of pergolide

1. The effect of pre-dosing with 15 mg domperidone, a relatively selective dopamine 2-receptor antagonist, on the ocular hypotensive action of a single oral dose of 25 micrograms pergolide, a dopamine 2-receptor agonist, was studied in 9 normal human volunteers, using a non-invasive method. 2. Compared with domperidone followed after 1 h by placebo, placebo followed after 1 h by pergolide had an ocular hypotensive effect in both eyes. Domperidone followed after 1 h by pergolide had no effect on intraocular pressure in both eyes. 3. The results of this study showed that domperidone inhibited the ocular hypotensive action of pergolide, suggesting that pergolide reduces intraocular pressure by the stimulation of the peripheral dopamine 2-receptors.

A comparison of the ocular hypotensive effect of 0.025% bromocriptine and 0.25% timolol eye drops in normal human volunteers

1. The ocular hypotensive effect of 0.025% bromocriptine and 0.25% timolol eye drops was compared in nine healthy human volunteers, using non-contact tonometry. 2. Considering all post-dosing measurements compared with placebo and including the baseline values as continuous independent variables, using multiple linear regression analysis, both bromocriptine and timolol had a significant ocular hypotensive effect (P less than 0.0001) in the treated eye with a significant but lesser effect in the contralateral eye. 3. In the concentrations used, timolol was more efficacious than bromocriptine in lowering intraocular pressure (P less than 0.025). 4. Using other forms of vehicles for bromocriptine to improve efficacy and studying the ocular hypotensive effect of topical application of other dopamine-2-receptor agonists such as pergolide and lisuride was suggested.

The effect of a single oral dose of pergolide on intraocular pressure and pupil diameter

1. The ocular hypotensive effect of a single oral dose of 25 micrograms pergolide, a dopamine 2-receptor agonist, was studied in 12 normal human volunteers, using a non-invasive method. 2. An oral dose of timolol 20 mg was used as a positive control. 3. The effects of both drugs on pupil diameter were also studied, using a photographic method. 4. Considering the first 6 h post-dosing measurements, using multiple linear regression analysis comparing drug with placebo and including the baseline values as continuous independent variables, both pergolide and timolol had a significant ocular hypotensive effect in both eyes (P less than 0.0001) with no significant effects on pupil diameter. 5. Further topical application studies in normal and glaucomatous eyes are needed to evaluate the usefulness of pergolide in the treatment of glaucoma.

The effects of lisuride, terguride and bromocriptine on intraocular pressure (IOP)

1. The effects of a single oral dose of the dopaminergic agonists lisuride (0.1 mg), terguride (0.25 mg) and bromocriptine (1.25 mg) on IOP were studied in eight normal volunteers using the non-contact tonometer. 2. Considering all post-dose measurements, compared with placebo, bromocriptine and lisuride but not terguride reduced IOP significantly in both eyes. 3. There was no significant difference between the ocular hypotensive effect of bromocriptine and lisuride. 4. Terguride reduced IOP significantly in the left eye at the 3 h time point after drug administration. 5. The result of this study confirms the reported ocular hypotensive effect of bromocriptine and showed that lisuride is as effective as bromocriptine in reducing IOP. 6. To evaluate the clinical importance of these drugs as ocular hypotensive agents other studies are needed using eye drops.

Aporphine derivatives affect ocular function in diverse ways

The sympathetic nervous system has been implicated in the ocular effects of several classes of dopamine receptor agonists. Two agonists of the aporphine class, (-) N-propylnorapomorphine [-)NPA) and norapomorphine (NA), were evaluated for effects on intraocular pressure (IOP) and pupil diameter (PD) in cats and normal (NL) and sympathectomized (SX) rabbits and on contractions of the cat nictitating membrane (CNM). Topically administered (-)NPA produced a monophasic IOP drop in the ipsilateral eye and a biphasic (increase, decrease) IOP response in the contralateral eye of normal rabbits. Pupil diameter increased bilaterally. In NL cats, the ipsilateral IOP and PD response to (-)NPA was biphasic (increase, decrease) and the contralateral IOP response was monophasic (increase). (-)NPA produced an increase in spontaneous motor activity (SMA) in rabbits and cats. NA lowered IOP unilaterally in NL rabbits. In SX rabbit eyes, (-)NPA lowered IOP as much as in NL eyes but with less mydriasis. NA did not lower IOP in SX rabbit eyes. Both (-)NPA and NA inhibited contractions of the CNM elicited by electrical stimulation of the pre- and post-superior cervical ganglionic nerves. (-)NPA, but not NA, inhibited contractions elicited by exogenous norepinephrine. These results suggest that aporphine derivatives produced two diametrically opposed effects on ocular function; 1) a centrally mediated effect that enhanced noradrenergic activity to elicit mydriasis, SMA and ocular hypertension, and 2) a peripherally mediated effect to produce miosis and ocular hypotension.