To determine the effects of the kappa opioid agonist, bremazocine (BRE), on intraocular pressure (IOP) and aqueous humor dynamics in normotensive cynomolgus monkeys.

IOP, pupil diameter, refraction, aqueous humor flow, and mean arterial pressure (MAP) were measured following unilateral topical application of 1 to 100 μg BRE. IOP and MAP responses to 100 μg BRE were repeated during intravenous infusion of angiotensin II (ATII). IOP and MAP responses to BRE were also measured following pretreatment with the opioid receptor antagonists norbinaltorphimine (nor-BNI) or naloxone. Outflow facility was measured following unilateral intracameral exchange with 0.01 to 100 μg/mL BRE. IOP, aqueous humor flow, pupil, and MAP were measured after unilateral intracameral bolus injection of 1 μg of BRE.

Unilateral topical BRE caused a dose-related reduction in IOP and aqueous humor flow in both eyes and in MAP. Pupil miosis occurred at the 100-μg dose. There was no effect on refraction. IOP and MAP decreases after 100 μg of BRE were eliminated by ATII infusion. Differential IOP effects after 10-μg topical BRE doses were not eliminated by nor-BNI or naloxone. Unilateral intracameral bolus injection of BRE decreased IOP in both eyes but had no effect on MAP or aqueous humor flow. Outflow facility was unchanged after intracameral exchange with BRE.

The IOP response to high doses of BRE in monkeys can be attributed to peripheral or central effects on MAP. The IOP-lowering response to topical BRE is due to aqueous humor flow suppression via non-opioid receptor stimulation. Some components of the IOP response are mediated by unknown mechanisms.