Cholinergic stimulation of lactoferrin and epidermal growth factor secretion by the human lacrimal gland

The human lacrimal gland produces tear proteins, such as lactoferrin and epidermal growth factor (EGF), that have presumed biologic activity on the ocular surface. We hypothesized that secretion of these tear proteins by the lacrimal gland is neurally mediated. To test this hypothesis, we evaluated the secretion of lactoferrin and EGF from the human lacrimal gland (LG) after cholinergic stimulation. Human LG biopsies from two donors were sliced into sections weighing approximately 100 mg and were serially placed in wells containing Dulbecco's modified Eagle's medium (DMEM/F12; with or without atropine), followed by media alone, media containing carbamylcholine chloride (carbachol), and then media alone, each for 10 min. Supernatants were then assayed for lactoferrin and EGF by antibody sandwich enzyme-linked immunosorbent assay (ELISA). Both sets of LG explants showed statistically significant increases in supernatant concentrations of lactoferrin and EGF 10 min after cholinergic stimulation. These returned to prestimulation concentrations by 20 min. Atropine-pretreated explants showed no significant change in supernatant concentrations of these proteins after carbachol stimulation. The results of these studies indicate that cholinergic stimulation of the human LG results in increased secretion of the tear proteins lactoferrin and EGF. This suggests that the LG can respond to the ocular surface environment by increasing secretion of biologically active tear constituents through neural stimulation.