Expression of nitric oxide synthase isoforms in lacrimal glands of rats

Aim: The present study was conducted to investigate the distribution of nitric oxide synthase isoforms (endothelial, neuronal, and inducible NOS) and changes in endothelial NOS (eNOS) expression after intraperitoneal injection of N(G)-Nitro-L-arginine methyl ester (L-NAME) in rats. Methodology: Immunohistological and immunoelectron microscopic study, using monoclonal mouse anti-endothelial NOS, anti-neuronal NOS and anti-inducible NOS were performed on the exorbital lacrimal glands of rats. Results: eNOS-positive immunoreactivities were observed in the intralobular ducts and interlobular ducts of exorbital lacrimal gland of rats. One day after L-NAME administration, the size of eNOS-positive immunoreactivities had significantly decreased, however, after 3 and 5 days of L-NAME administration, eNOS-positive immunoreactivities were restored. Neuronal NOS-positive immunoreactivity was observed in nerve fibers of exorbital lacrimal gland, but was not detected in the duct systems or in the acinar cells. The inducible NOS was not detected in the exorbital lacrimal glands of rats. Interpretation: Expression of nNOS in the nerves of lacrimal gland suggests that NO may play a role in modulating tear production. eNOS and nNOS were expressed in the exorbital lacrimal glands of rats, and the endogenously located eNOS was influenced by NOS inhibitor (L-NAME). These results suggest that endogenous NOS may be closely related with the direct or indirect regulation of glandular secretion and blood flow in the exorbital lacrimal glands.