Secretion of glandular kallikrein and renin from the basolateral pole of mouse submandibular duct cells: an immunocytochemical study.

Glandular kallikrein from salivary glands in rats has been measured in the circulation and has been shown to have local vasoactive effects. In mice, renin and epidermal growth factor from the submandibular gland (SM) also reach the circulation, as both have been measured in plasma. The route by which these peptides enter the blood from their site of synthesis in ducts of the SM is unclear. We have investigated by immunocytochemistry the secretory pathways for kallikrein and renin from salivary duct cells in mice. The renal/pancreatic kallikrein-secreting cells of the striated and excretory ducts of the SM were distinguished from the granular convoluted tubule (GCT) cells which secrete other glandular kallikreins on the basis of data obtained in previous studies, in which we used gene-specific oligonucleotide probes to identify the expressing cell types. Renal/pancreatic kallikrein was apparently secreted constitutively from the basolateral surface of striated duct cells and in secretory vesicles from excretory duct cells, whereas apical secretion occurred via the regulated pathway in both cell types. Glandular kallikreins and renin synthesized in GCT cells were secreted from the basolateral surface by dissolution of granules at the cell membrane. There were fenestrated capillaries underlying the duct tree which would enable the secreted products to reach the circulation.