C-type Natriuretic Peptide (CNP) and its receptors in the rat lacrimal gland

The present study investigated the presence and possible roles of the immunoreactive (ir) C-type natriuretic peptide (CNP) and its receptor in the rat exorbital lacrimal gland. The serial dilution curve of lacrimal gland extracts was parallel to the standard curve of synthetic CNP_(1-22). Molecular profiles using gel permeation HPLC showed that irCNP in lacrimal gland extracts was coeluted in the position of authentic CNP_(1-22). The irCNP content was about 3 pg/mg protein. Strong CNP immunoreactivities principally localized in the tubules and excretory ducts, and moderate CNP immunoreactivities also localized in the acini of the gland. Interestingly, ANP immunoreactivities colocalized in the same sites. mRNA s for CNP and ANP were also detected in lacrimal gland by RT-PCR. Production of 3′5′-cyclic guanosine monophosphate (cGMP) by particulate guanylyl cyclase in lacrimal gland membrane was stimulated by natriuretic peptides in a dose dependent manner. cGMP production was more highly elevated by CNP compared with ANP and BNP. mRNA of the GC coupled natriuretic peptide receptors were detected by RT-PCR. These results indicate that CNP and its specific receptor are expressed in the rat lacrimal gland, and suggest that CNP may act as a local autocrine and/or paracrine regulator via activation of NPR-B subtype.