Development of secretory activity in serous cells of the rat tongue. Cytological differentiation and accumulation of lingual lipase

The development of the serous cells of the rat tongue was studied by light and electron microscopy and compared with the accumulation of lingual lipase, measured by triglyceride hydrolysis at pH 5.4. The lingual serous (von Ebner's) glands were initiated in 19- to 20-day fetuses as epithelial ingrowths from the vallate and foliate papillae. The cells contained mostly free polyribosomes, few RER cisternae, and a small Golgi apparatus. Branching of the cell cords began shortly after initiation, but formation of acini and production of secretory granules did not begin until 3–4 days postnatally. The acinar cells had abundant basal RER, a supranuclear Golgi apparatus, and apical secretory granules and attained adult appearance by 17–25 days. The serous demilune cells of the lingual mucous glands differentiated more rapidly than the lingual serous acinar cells, attaining functional secretory structure in Day 20 fetuses. Lipase activity was first detected in Day 20 fetuses and increased 14-fold by birth. The activity decreased 50% during the first suckling period, returned to birth levels 1 day later, and increased rapidly thereafter. By 17 days postnatally, lipase activity was 23% of the adult level, although activity per gram body weight was equal to the adult. The results suggest that lingual lipase is produced prenatally by the demilune cells of the lingual mucous glands and postnatally predominately by the lingual serous glands. Lingual lipase may play an important role in lipid digestion in neonates, when levels of pancreatic lipase are low.