Sialic acid in rabbit lacrimal gland fluid.

To date, there has been no attempt to determine which of the orbital glands contribute the sialic acid, which has been found in tears and tear mucoids. In the present study, sialic acid was found in the fluid collected directly from the lacrimal gland excretory duct, uncontaminated by the secretions of the other orbital glands (Nictitans, Harderian, conjunctival) as well as in the fluid secreted into the conjunctival sac by the other orbital glands, uncontaminated by lacrimal gland fluid. At all flow rates, the rate of secretion of sialic acid increased as flow rate increased in both fluids and the rate of secretion of sialic acid by the lacrimal gland was three times that by the other orbital glands. This is the first demonstration that a substance, which can be derived from either nonserum glycoproteins, such as the tear mucoids, or alpha-globulins, is a component of the secretions of the lacrimal gland, as well as of the secretion of the other orbital glands.