Expression and distribution of parotid secretory proteins in experimental diabetes.

Previous studies of experimental diabetes have demonstrated changes in the levels of specific salivary proteins. The present study is part of a larger effort aimed at elucidating the mechanism(s) by which insulin regulates salivary protein expression in the rat parotid gland. Diabetes was induced in 2-3-month-old male Fischer 344 rats by injection of streptozotocin (STZ). After 30 days one group of rats was given insulin for 7 days. Untreated rats served as controls. As previously observed, parotid acinar cells from diabetic rats accumulated lipid and contained occasional crystalloid lysosomes. Quantitative immunogold labeling of secretory granules in diabetic glands revealed decreases of 30-60% for proline-rich-proteins (PRPs), amylase and parotid secretory protein (PSP), but labeling for acidic epididymal glycoprotein (AEG) was unchanged. The response to insulin treatment was variable: amylase and PSP labeling were partly restored, but PRP and AEG labeling showed little change. Photoaffinity labeling of cyclic AMP receptor proteins (cARP) showed changes in several tissues including a consistent increase in the diabetic parotid gland. Immunogold labeling of secretory granules with antibody to cARP was similar in control and diabetic parotids, but nuclear and cytoplasmic label was decreased in diabetic acinar cells. These results indicate that STZ-diabetes and insulin reconstitution cause variable changes in the expression of parotid secretory proteins. Changes in cARP levels suggest that the insulin and cyclic AMP pathways may interact in regulating expression of salivary secretory proteins.