Effects of Neuropeptides on Serotonin Release and Protein and Peroxidase Secretion in the Isolated Rat Lacrimal Gland

Abstract

The secretion of tears by the lacrimal gland is regulated by the autonomic nervous system¹ and by non-cholinergic, non-adrenergic (NCNA) nerves that are believed to release a number of biologically active peptides that can function as neurotransmitters of NCNA nerves regulating the secretory processes.^2,3 The neuropeptides have been investigated for their potential role in modulating the immune system. In many organs and tissues from several animal species, a morphological and functional association was found between mast cells and neuropeptide-containing nerves that contain substance P (Sub P) and calcitonin gene-related peptide (CGRP), or both.^4,5 Mast cells have a secretory capacity. They released mediators which include serotonin (5-HT), and histamine which can evoke pronounced biological effects resulting in cellular regulation.⁶ It is now apparent that neuropeptides can modulate some immune response directly,⁷ and several peptides--in particular, Sub P have been shown to induce mast cell mediator release.⁸ It is possible that neuropeptides may function as immunological effectors in inflammatory responses in the lacrimal gland. Moreover, in a previous study we showed that the lacrimal gland is innervated with numerous neuropeptides, and there is a consistent association between peptidergic nerves and mast cells.⁹ This study was designed to investigate any functional interaction between mast cells and peptidergic neurotransmitters Sub P and CGRP.