Morphine-induced reduction of intraocular pressure and pupil diameter: role of nitric oxide.

The present study was performed to evaluate the role of nitric oxide in the intraocular pressure (IOP) lowering effect and in the miotic action of morphine. The IOP was measured in conscious, normal, dark-adapted New Zealand white rabbits using a calibrated pneumatonometer. Experiments were conducted, in which rabbits' eyes were treated with morphine topically and unilaterally, while the fellow eyes received vehicle.

Bremazocine increases C-type natriuretic peptide levels in aqueous humor and enhances outflow facility.

A relatively selective agonist of kappa opioid receptors (KOR), bremazocine (BRE), lowers intraocular pressure in rabbits, in part, by increasing natriuretic peptide levels in aqueous humor and by enhancing total outflow facility (TOF). Natriuretic peptide (NP) levels [atrial NP (ANP), brain NP (BNP), and C-type NP (CNP)] were measured in aqueous humor of rabbits either by radioimmunoassay or enzyme immunoassay. TOF was determined in rabbits by two-level constant pressure perfusion of the anterior chamber.

Dynorphin modulates ocular hydrodynamics and releases atrial natriuretic peptide via activation of kappa-Opioid receptors.

The present study was designed to investigate the effect of the kappa opioid receptor (KOR) agonist, dynorphin A (Dyn), on aqueous humor dynamics (intraocular pressure (IOP), aqueous humor flow rate (AFR)), pupil diameter (PD) and atrial natriuretic peptide (ANP) levels in the aqueous humor of the rabbit. Topical and unilateral application of Dyn caused dose-related, bilateral reductions in IOP and AFR. An intermediate dose of Dyn (33 microg) caused bilateral mydriasis whereas a higher dose (100 microg) caused unilateral miosis.