Comparative Effects of Alpha-2 and DA-2 Agonists on Intraocular Pressure in Pigmented and Nonpigmented Rabbits

Abstract

Alpha-2 and DA2 adrenoceptor agonists produce ocular hypotension in cats, rabbits, monkeys and humans. In this study,the effects of topical, unilateral administration of medetomidine (MED), an alpha-2 agonist, and Ha-118 (HA), a DA2 agonist, were compared on intraocular pressure (IOP) in normal, unilaterally sympathectomized (SX), and ocular hypertensive (oral water loaded) Dutch Belted (DB) and New Zealand White (NZW) rabbits. MED (75pg) produced bilateral ocular hypotensive effects in both DB and NZW normal rabbits; however, HA (250pg) lowered IOP unilaterally in NZW rabbits only . MED (25pg) inhibited the rise in IOP caused by oral water loading in both DB and NZW rabbits; HA, on the other hand, was effective only in NZW rabbits.

Lisuride Acts at Multiple Sites to Induce Ocular Hypotension and Mydriasis

“…Previous studies revealed that a variety of DA 2 agonists induce ocular hypotension in laboratory animals [15][16][17] and humans [6][7][8][9][10]. In normal and sympathectomized rabbits, lisuride induced a rather transient IOPlowering effect which lasted for 1-2 h. Compared to other DA 2 agonists, the short duration of the ocular hypotensive effect and the mydriatic response of lisuride suggested that lisuride activates not only DA 2 receptors in the eye but also sites in the central nervous system.…”

The effect of intravenous medetomidine on pupil size and intraocular pressure in normotensive dogs

“…Peripheral a-2 receptors in the eye, both prejunctionally on ocular sympathetic nerve fibres and postjunctionally, are potentially involved in the physiological regulation of IOP. This regulation is achieved by decreasing the stimulated production of cyclic AMP in the ciliary process (4,5). To our knowledge, the effect of medetomidine on the IOP and pupil diameter of the canine eye has not been described previously.…”

“…MedeDepartment of Clinical Sciences of Companion Animals, Faculty of Veterinary tomidine is commonly used to sedate animals for non-surgical interventions, such as oral inspection or radiography or as a premedication before general anaesthesia. Studies of normotensive rabbits and cats have demonstrated that medetomidine lowers the IOP after its topical application to the eye (4,5). Peripheral a-2 receptors in the eye, both prejunctionally on ocular sympathetic nerve fibres and postjunctionally, are potentially involved in the physiological regulation of IOP.…”

Repeatability, reproducibility, and agreement of three tonometers for measuring intraocular pressure in rabbits

“…In dogs, no reduction of IOP has been observed using a similar dose of 0.5 mg/kg medetomidine IM 100 . In rabbits, medetomidine has also topically been instilled 18 , 19 . Two studies found that a dose of 25 μg medetomidine reduced the IOP of the contralateral eye in 30 min by ~ 50%, while the treated eye was not affected 18 , 19 .…”

“…In rabbits, medetomidine has also topically been instilled 18 , 19 . Two studies found that a dose of 25 μg medetomidine reduced the IOP of the contralateral eye in 30 min by ~ 50%, while the treated eye was not affected 18 , 19 . This effect has also been observed in dogs 101 .…”