Submandibular and Sublingual Glands Bind the C-terminal Tetrapeptide of Gastrin/cholecystokinin

Objectives: Could salivary glands contain enteric peptides to prime the stomach's reception of food? Might submandibular (SMG) and sublingual (SLG) glands contain gastrin whose C-terminal tetrapeptide also occurs in cholecystokinin (CCK)? Methods: In each of six adult rats of both sexes one of each gland was excised, formalin-fixed and paraffin-embedded. Immunohistochemistry employed a rabbit polyclonal antibody (Cell Marque, Hot Springs, AR) marketed as an anti-human Gastrin I which cross-reacts with CCK. Our findings reveal its cross-reaction with rat tissues. Deparaffinized sections were boiled in citrate buffer. Endogenous peroxidase was blocked and either the antibody or a rabbit immunoglobulin fraction as the negative control was applied, followed by a horseradish peroxidase anti-rabbit link, DAB chromogen, and hematoxylin counterstain. Results: SMG serous acini, many with pan-cytoplasmic granulation, stained more heavily than the ducts which contained apical granules and blebs. The SLG's mucous acini were unreactive but its ducts had some brown nuclei and apical granules, some in the lumen. Thus, these glands contain gastrin and/or CCK. To distinguish them, aliquots of the antibody were preabsorbed. Preabsorption with gastrin leaves the antibody reactive for CCK, and with CCK leaves it reactive for gastrin. Unexpectedly, because salivary glands are nearer the stomach where gastrin is made than the intestine where CCK is made, most SMG myoepithelial cells, acini and ducts, and most cells of the SLG duct system immunostained more heavily for CCK than for gastrin. SMG acinar cell heterogeneity was much greater for gastrin than for CCK. Conclusion: Both rat SMGs and SLGs contain appreciable CCK but less gastrin. As both were in the duct lumens they likely enter saliva. Because mastication increases salivary flow, and therefore swallowing, both could act in the stomach before the bulk of these enteric peptide hormones are released from their primary sources during meals.