Atrial Natriuretic Peptide System in Eyes

ABSTRACT

Atrial natriuretic peptide(ANP), a peptide hormone synthesized mainly in the cardiac atrium, has an important physiological role on the regulation of body fluid and electrolyte balance. Extraatrial ANP system has been reported. The presence of ANP in eye has also been reported. ANP in the eye has claimed to control the intraocular pressure. However, the presence of ANP and its receptors in the intraocular tissues are controversial. Therefore, the purpose of the present study was to determine the characteristics of molecular nature of ANP and its receptors in variable intraocular tissues of cow. Immunoreactive ANP was detected in aqueous humor(10+/-1 pg/ml), cornea (3.6+/-0.5 pg/mg), ciliary body(2.62+/-0.6 pg/mg), choroid(2.1+/-0.5 pg/mg), retina (1.7+/-0.2 pg/mg)and iris(1.4+/-0.5 pg/mg). Chromatographic characterization of molecular profile of ANP showed major peak corresponding to small molecular weight forms of ANP and minor peak corresponding to proANP. ANP mRNA was detected in the cornea, retina and ciliary body using reverse transcriptase-polymerase chain reaction. The production of cGMP by the activation of guanylyl cyclase was stimulated by ANP, BNP and CNP in tissue membranes of cornea, ciliary body and iris. Autoradiographic study showed that the corneal endothelium had A, B, and C subtypes of natriuretic peptide receptor. Longitudinal fibers of ciliary muscle and retina had A subtype of natriuretic receptor. These results suggest that the bovine eye has its own ANP system and ANP may have an important paracrine or autocrine function in the eye.