Involvement of Dopamine D1-Like Receptors in Mediating Increases in Protein Secretion from Rabbit Lacrimal Gland

Abstract

ABSTRACT

To identify and localize the dopamine receptor subtypes in rabbit lacrimal gland which mediate protein secretion, the effects were determined of different dopamine receptor subtype agonists, antagonists, and a β adrenergic antagonist on this process. Protein secretion into the medium was quantified with the Bradford assay. Dopamine increased protein secretion between 10⁻⁷ and 10⁻⁴M, and it could be maintained for a subsequent 80 min. The relatively selective D1-like receptor agonist, SKF-38393 (10⁻⁴M) had a similar effect which was suppressed by the D1-like receptor antagonist, SCH-23390. However, neither the D2-like receptor agonist, quinpirole (10⁻⁴M), nor the selective D2-like receptor antagonist, sulpiride (10⁻⁴M) altered either the basal level or the stimulated response to dopamine. The dopamine (10⁻⁴M)-elicited increases in protein secretion were completely suppressed in the presence of either 10⁻⁴M propranolol or 10⁻⁴M bretylium. Protein secretion in rabbit lacrimal gland is mediated by dopaminergic nerves through stimulation of the presynaptic D1-like receptor.