The rat exorbital lacrimal gland as a site of synthesis of EGF-like growth factors.

Abstract

The lacrimal gland produces the complex aqueous portion of tears that contains many components including electrolytes and proteins.1,2 The pH, electrolyte concentration, and protein composition of lacrimal fluids are crucial to maintain the health of the ocular surface. The proteins that lacrimal glands synthesize and secrete are very specific, but only a few of them have been characterized. These proteins are thought to be involved in the bacteriostatic action of tears. It has been shown that human3,4 and mouse5 tears contain epidermal growth factor (EGF) or an EGF-like immunoreactivity. The EGF precursor mRNA has been detected by Northern blot in moûse6 and by RT-PCR in human7 lacrimal glands. Moreover, EGF-like immunoreactivities have been detected in mouse,6 rabbit,8 and rat9,10 lacrimal tissues, but the immunoreactive proteins have not been further characterized. The EGF receptor mRNA has also been detected, by RT-PCR, in the human lacrimal gland,11 and by RT-PCR and Northern blot in the rat exorbital lacrimal gland.12 The EGF receptor protein has been identified and shown to be activated by EGF in the rat tissue.12