Melatonin does not increase IOP significantly in rabbits

Abstract

New Zealand white rabbits have a circadian rhythm of intraocular pressure; pressure is higher during the dark than during the light. We explored the possibility that the dark phase increase of serum and/or ocular melatonin plays a role in regulating the rhythm of intraocular pressure. Exogenous melatonin was delivered by four routes: topical application (0.1 and 10 micrograms), intravenous injection (1 microgram), intravitreal injection (9 micrograms) and intra-arterial infusion (50 ng and 1 microgram). Melatonin delivered by these routes did not increase intraocular pressure. We also measured the concentration of melatonin in the aqueous after unilateral intra-arterial infusion to confirm that melatonin delivered by this route reached the eye. The concentration was 419 +/- 99 and 109 +/- 17 pg/ml (n = 8, p < 0.025) in the ipsilateral and contralateral eyes, respectively. The concentration of melatonin in the aqueous after intra-arterial infusion of saline was less than the sensitivity of the assay (< 16 pg/ml, n = 6). The results of these experiments indicate that melatonin does not increase IOP significantly under the experimental conditions employed in this study.

Preliminary findings on the effect of melatonin on the clinical outcome of cataract surgery in dogs

“…In contrast, it has been demonstrated that oral or topical administration of melatonin reduces IOP in monkeys, rabbits, and humans . However, other studies did not find any effect of topical application, intravenous or intravitreal injection, and intra‐arterial infusion of melatonin on rabbit IOP . In addition, we have previously shown that the administration of melatonin as a subcutaneous pellet does not affect IOP in normal or glaucomatous rats .…”

“…44 However, other studies did not find any effect of topical application, intravenous or intravitreal injection, and intra-arterial infusion of melatonin on rabbit IOP. 45,46 In addition, we have previously shown that the administration of melatonin as a subcutaneous pellet does not affect IOP in normal or glaucomatous rats. 26 Although we do not have any explanation for this discrepancy, differences in species, administration route, and dose, as well as the particular ocular condition (eye submitted to PE), could account for it.…”

Melatonin: a novel neuroprotectant for the treatment of glaucoma

“…The effect of melatonin on IOP is still controversial. Several studies did not find any effect of topical application, intravenous or intravitreal injection, and intraarterial infusion of melatonin on rabbit IOP [39, 40], whereas other groups have demonstrated that oral or topical administration of melatonin reduces IOP in rabbits [41], monkeys [42], and humans [43]. In our experimental setting, a subcutaneous pellet of melatonin did not change IOP along 10 wk of treatment with HA.…”

Intraocular pressure in normal llamas (Lama glama) and alpacas (Lama pacos)

“…Baseline IOP using applanation tonometry has been determined for many species of animals, including dogs, cats, raptors, horses, ponies, dairy cows, ferrets, Nubian ibexes, Grant zebras, Arabian oryxes, rabbits, rats, alligators, and lions; 6 –17 however, to our knowledge a controlled study measuring baseline IOP in llamas and alpacas has not been reported.…”