Age-related changes in EGF and protease in submandibular glands of C57BL/6J mice

The submandibular glands of male C57BL/6J mice were studied cytologically and chemically at the following ages (months): 1-1.5, 6-8, 12-13, 28-32. The relative proportion of granular convoluted tubules (GCT), as well as the size and content of secretion granules of GCT cells, progressively increased throughout the first year of life. Correspondingly, the concentration within the glands of two GCT cell products, epidermal growth factor (EGF) and protease, also steadily increased. In senescent glands, GCTs formed relatively less of the gland parenchyma and were composed of shorter cells with reduced amounts of secretory granules. The concentration of EGF was reduced to 17% of its peak value at one year, while protease activity declined to 50% of its peak value. These morphologic and chemical findings imply a functional impairment in submandibular glands of the mouse with senescence.