Alteration in ocular function induced by phenylethylamine analogs of dopamine

Area of Science:

• Ophthalmology
• Neuropharmacology
• Physiology

Background:

• Dopamine (DA) and its methylated analogs are neurotransmitters with potential roles in ocular function.
• Understanding their effects on intraocular pressure (IOP) and pupil diameter (PD) is crucial for ophthalmological research.

Purpose of the Study:

• To investigate the effects of dopamine (DA) and its methylated analogs (N-methyldopamine, N,N-dimethyldopamine, N,N-di-n-propyldopamine) on IOP and PD in rabbits.
• To elucidate the mechanisms underlying these effects, including the involvement of extraocular muscles and sympathetic pathways.

Main Methods:

• Topical administration of DA and its analogs to normal, sympathectomized (SX), and extraocular muscle-transected (EOMX) rabbits.
• Measurement of IOP and PD.
• Assessment of responses to pharmacological interventions (timolol, metoclopramide) and physiological challenges (water loading, hypertonic saline infusion).
• Evaluation of effects on cat nictitating membrane preparation.

Main Results:

• DA, N-methyldopamine, and N,N-dimethyldopamine caused transient ocular hypertension in normal rabbits, linked to extraocular muscle contraction.
• N,N-di-n-propyldopamine induced bilateral ocular hypotension in normal rabbits, acting via a neuronal pathway.
• N-methyldopamine's hypotensive effect in SX rabbits was antagonized by timolol, suggesting beta-adrenoceptor involvement.
• Dopamine analogs differentially affected IOP regulation and aqueous humor formation.

Conclusions:

• Dopamine analogs exert varied effects on ocular parameters, mediated by distinct mechanisms.
• Extraocular muscles play a role in the initial ocular hypertensive response to some dopamine analogs.
• Neuronal pathways and beta-adrenoceptors are implicated in the ocular hypotensive effects of certain dopamine analogs.