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M. Lorber, E. Permaul, D. Berry; Lacrimal Gland Ducts Bind the Common Pentapeptide of Gastrin/Cholecystokinin. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4235.
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Tear drainage into the nasopharynx results in their being swallowed, thereby entering the alimentary tract. Accordingly, might the lacrimal gland contain enteric peptides to contribute to gastrointestinal functioning?
One exorbital lacrimal gland was excised from four adult rats of both sexes and fixed in buffered formalin. Immunohistochemistry was performed using a rabbit polyclonal antibody marketed by Biogenex (San Ramon, CA) as an anti-human gastrin which cross-reacts with cholecystokinin (CCK) and with rat tissues. Because gastrin and CCK have a COOH-terminal pentapeptide in common, immunostaining indicates the presence of either or both. The protocol involved deparaffinizing 5µm sections, epitope retrieval at 98oC for 20 min in pH 6 citrate buffer followed by cooling, room temperature incubation with: 3% H2O2 for 10 min to block endogenous peroxidase, then with 10% non-immune goat serum for 10 min, the primary antibody diluted 1:50 for 1 h, a biotin-conjugated secondary anti-rabbit antibody for 10 min, horseradish peroxidase-conjugated streptavidin for 10 min, DAB chromogen for 5 min, and counterstaining by hematoxylin for 2 min, dehydration and mounting. Rinsing with buffered saline was performed between almost all steps. The positive control was rat antrum, the negative control omitted the primary antibody.
Neither the acini nor the myoepithelial cells immunostained. However, many of the nuclei of the intercalated ducts did so, accompanied by slight cytoplasmic immunostaining. The intralobular ducts exhibited immunostaining of essentially all nuclei with moderate cytoplasmic staining. In the interlobular ducts most nuclei immunostained and their cytoplasm generally did so strongly, often with abundant bleb formation. The collecting ducts exhibited the least reactivity. Adipose and mast cells did not immunostain. The negative control slides did not immunostain.
Rat exorbital lacrimal gland ducts have receptors that bind the pentapeptide common to both gastrin and cholecystokinin. Either or both of these enteric peptides are present in lacrimal tissues. Because immunostained cytoplasmic blebs both border and lie within many of the duct system lumens, their contents would be in tears. Their drainage into the nasopharynx and subsequent swallowing allows tears to make a slight contribution to alimentary tract physiology.
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