Rat lingual lipase: factors affecting enzyme activity and secretion

The lingual serous glands of rat tongue secrete a potent lipase that acts in the stomach in which it initiates the digestion of dietary fat. The subcellular localization of the enzyme and factors affecting its activity and secretion were studied in adult male Sprague-Dawley rats. In a fraction rich in secretory granules, 42% of the lipase content of lingual serous glands was recovered after fractionation of homogenates of discontinuous gradients of urografin in 0.3 M sucrose. Lipase secretion was stimulated by isoprenaline: 2 h after isoprenaline administration, the lipase content of lingual serous glands was 73 +/- 5% lower than that of the control group. Accumulation of lipase began 8 h after the injection, reaching 57 +/- 7% of the initial level of the control group after 25 h. Bilateral resection of the glosso-pharyngeal nerves or bilateral sympathectomy led to a 40--50% decrease of enzyme activity in 7 days. Enzyme activity was markedly affected by the fat content of the diet. Feeding a high-fat diet (22% corn oil) for a period of 2 wk led to a 45% increase in the lipase content of lingual serous glands. The exponential rise in the lipase activity of the lingual serous glands immediately after birth could be related to the high-fat content of rat milk. The data suggest that the lingual serous glands are similar to other exocrine glands such as pancreas and parotid gland in the subcellular localization of secretory enzymes and mechanisms of enzyme secretion.