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M. Lorber, E. C. A. Permaul, S. Sen, D. L. Berry; Immunoreactive Cholecystokinin (CCK-8) is Present in Human Lacrimal Glands. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4165.
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Tears drain into the nasopharynx, are swallowed and so enter the G.I. tract. Could they have enteric peptides which might both affect tear secretion and the G.I. tract?
Four lacrimal glands were removed from embalmed cadavers as described by Lorber & Vidic (Orbit 28:137-146, 2009). They were fixed, perhaps unnecessarily, in buffered formalin and embedded. Immunohistochemistry employed a rabbit antiserum marketed as Anti-Cholecystokinin (26-33) (sulfated CCK-8) by Sigma-Aldrich. It has cross-reactivities with human Gastrin I of 0.2%, and of 1% with human Big Gastrin, so is essentially specific for CCK-8. Five µm sections were deparaffinized. The VectaStain kit (Vector Labs) was used. Epitope retrieval with citrate was at 98oC. Incubation with 3% H2O2 blocked endogenous peroxidase. Subsequent steps employed 10% normal goat serum, the primary antibody diluted 1:1150, biotin-conjugated anti-goat secondary antibodies, VectaStain avidin/biotinylated enyme complex, DAB chromogen, and hematoxylin counterstaining. The positive control was proximal duodenum. The negative control omitted the primary antibody.
Lacrimal acinar cells stained variably. Their nuclei were generally negative. Cytoplasmic staining of low intensity was restricted to the cell base. If of high intensity the entire cytoplasm and at times the nucleus stained. Myoepithelial cell (M-E) nuclei stained moderately, as often did their adjacent cytoplasm. Duct nuclei were generally negative, except for the basal cells in the larger ducts. Typically, ductal epithelium stained more deeply than acinar or M-E cells, many duct cells having intense apical cytoplasmic staining. Larger duct lumens often contained immunostained cellular debris.
Human lacrimal glands bind an antibody to CCK-8. Immunoreactive CCK in M-E cells and its predominantly basal binding in acinar cells suggests circulating CCK enters the lacrimal gland via the transudate. The largely apical distribution in duct cells suggests secretion which is confirmed by the presence in duct lumens of immunostained cellular debris which would then enter tears. These localizations reflect CCK's properties in the alimentary tract. There, CCK causes smooth muscle contraction in the pylorus, duodenum, and gallbladder, as presently noted in the lacrimal M-E cells; and exocrine secretion from the liver and pancreas, as is also evidenced in lacrimal duct lumens. If CCK is not destroyed by gastric juice, swallowing tears would also allow lacrimal CCK to contribute slightly to alimentary physiology.
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