-1 Adrenergic and Cholinergic Agonists Increase EGF mRNA Expression in Rat Lacrimal Gland

Abstract

Abstract: : Purpose: Nerves and growth factors are two important regulators of lacrimal gland secretion. Epidermal growth factor (EGF) is a stimulator of protein secretion. The lacrimal gland is also thought to be a main source of EGF in tear film. To determine if nerves stimulate EGF production in lacrimal gland, we studied the effects of α-₁ adrenergic and cholinergic agonists on EGF mRNA expression in rat lacrimal gland. Methods: Exorbital lacrimal glands were removed from male Sprague-Dawley rats. Acini were isolated by collagenase digestion and incubated with the α-₁ adrenergic agonist phenylephrine or the cholinergic agonist carbachol at 10^-4M for 10 min to 18 hrs. Total RNA was isolated and semiquantitative RT-PCR was performed to investigate mRNA expression of the EGF gene. The G3PDH gene was used as the internal control. The amount of PCR product was expressed as the ratio of the amplified EGF gene to the G3PDH gene. Results: RT-PCR amplification of rat lacrimal gland acini generated a band of the predicted size for EGF mRNA. The level of EGF mRNA expression was significantly elevated after stimulation with either α-₁ adrenergic or the cholinergic agonists. Phenylephrine increased EGF mRNA expression with the maximum of a 2.0 fold increase at 1 hour after stimulation. Carbachol increased EGF mRNA expression with the maximum of a 2.3 fold increase at 30 min after stimulation. After the peak increase in mRNA expression, there was a progressive decline under both conditions. Conclusion: EGF mRNA expression is increased in rat lacrimal gland acini in response to α-₁ adrenergic and cholinergic agonists, suggesting that the synthesis of EGF in lacrimal gland seems to be under neural control.

Keywords: lacrimal gland • growth factors/growth factor receptors • signal transduction