Ocular hypotension induced by intravitreally injected C-type natriuretic peptide

Area of Science:

• Ophthalmology
• Endocrinology
• Physiology

Background:

• Intraocular pressure (IOP) regulation is crucial for ocular health.
• C-type natriuretic peptide (CNP) is a vasoactive peptide with potential roles in fluid balance.
• Understanding the mechanisms of IOP control is vital for managing glaucoma.

Purpose of the Study:

• To investigate the effect of intravitreal c-type natriuretic peptide (CNP) on intraocular pressure (IOP) in rabbit eyes.
• To determine CNP's impact on aqueous humor dynamics and cyclic guanosine monophosphate (cGMP) levels.
• To examine the presence of CNP-like immunoreactivities (CNP-LI) in ocular tissues of rabbits and pigs.

Main Methods:

• Intravitreal injections of varying doses of CNP were administered to rabbit eyes.
• Intraocular pressure (IOP) was measured post-injection.
• Aqueous humor dynamics (flow, outflow facility) and cGMP concentration were assessed.
• Radioimmunoassay and monoclonal antibody techniques were used to detect CNP and CNP-LI in ocular fluids and tissues.

Main Results:

• Intravitreal CNP administration led to a dose-dependent reduction in IOP.
• CNP significantly increased total outflow facility by approximately 35% without altering aqueous humor flow or uveoscleral outflow.
• cGMP concentration in the aqueous humor of CNP-treated eyes increased significantly (4- to 14-fold).
• CNP-LI were identified in the ciliary body epithelium of both rabbit and porcine eyes.

Conclusions:

• Intravitreal CNP effectively lowers IOP in rabbits, primarily by enhancing uveoscleral outflow.
• The observed increase in cGMP suggests a signaling pathway mediating CNP's effects on IOP.
• CNP and its associated immunoreactivities are present in ocular tissues, indicating a potential endogenous role in IOP regulation.