Correlation between vasodilatation and secretion in the lacrimal gland elicited by stimulation of the cornea and facial nerve root of the cat.

PURPOSE To determine whether reflex vasodilatation can be elicited in the cat lacrimal gland by electrical stimulation of the cornea, whether the vasodilatation elicited by electrical stimulation of the facial nerve root found to be the efferent arm of the cornea-lacrimal gland reflex pathway correlates with the evoked secretion in the lacrimal gland, and what kind of receptors and which autonomic ganglia are involved in lacrimal vasodilator and secretory responses. METHODS Electrical stimulation of the cornea or facial nerve root was used to evoke a blood flow increase in the lacrimal gland and tear secretion of the urethane-chloralose-anesthetized, paralyzed, and cervically sympathectomized cat. RESULTS The lacrimal vasodilator response depended on stimulus intensity and frequency and correlated well with the tear secretion. Injection of 2% lidocaine solution into the retrobulbar area, where the pterygopalatine ganglion is located, abolished the vasodilator and the secretory responses. Pretreatment with hexamethonium (an autonomic ganglion blocker) greatly attenuated the secretory response, even at a low dose (1 mg/kg given intravenously), although at this dose, the vasodilator response was only slightly affected. Neither phentolamine (an alpha-adrenoceptor antagonist) nor propranolol (a beta-adrenoceptor antagonist), nor a vasoactive intestinal peptide antagonist had any effect on the vasodilator or secretory responses. Scopolamine (a muscarinic receptor antagonist), although having no effect on vasodilatation, had a profound inhibitory effect on the secretory response. CONCLUSIONS These results suggest that whereas the vasodilator and secretory responses in the lacrimal gland were well correlated, they were mediated by different mechanisms.