Immunohistochemistry and Secretory Effects of Leucine Enkephalin in the Isolated Pig Lacrimal Gland

Abstract

The innervation of the lacrimal gland is provided mainly by the parasympathetic nerves and to a lesser extent by the sympathetic nerves of the autonomic nervous system.^1–3 The sites of nerve termination vary from species to species, but in general they seem to terminate near blood vessels and basement membrane of secretory acini and ducts. Stimulation of parasympathetic nerves resulted in the release of acetylcholine, which in turn activates cholinergic muscarinic receptors. This leads to the metabolism of phosphatidylinositol 1,4- bisphosphate, resulting in cellular calcium mobilization.^2,3 On the other hand, stimulation of adrenergic nerves results in the release of noradrenaline, which activates both α— and β—adrenergic receptors, resulting in the mobilization of Ca²⁺ and the metabolism of adenosine 3,5-cyclic monophosphate, respectively.^2,3 In addition to parasympathetic and sympathetic nerves, there is, much evidence for the presence of noncholinergic, non-adrenergic nerves that contain a number of neuropeptides, some of which can elicit lacrimal protein secretion.^2–4 However, the distribution and secretory effects of enkephalin-related peptides in the lacrimal gland of the pig is less understood despite its close morphological relation to man. This study investigates the localization of leucine enkephalin (LEU-ENK) and its involvement with lacrimal protein secretion.