Secretion of lingual lipase and amylase from rat lingual serous glands

The effects of various secretagogues on the release of lingual lipase and amylase from rat lingual serous glands was examined in vitro and in vivo. After incubation, the media and tissues were assayed for lingual lipase and amylase activity to determine percent of secretion. In vitro secretion of lingual lipase and amylase stimulated by the cholinergic agonist, carbamylcholine chloride (carbachol), was 28.3 +/- 1.7, 48.0 +/- 3.2, and 55.9 +/- 2.4% and 18.1 +/- 1.7, 26.4 +/- 3.0, and 28.0 +/- 2.5%, respectively, for 30-, 60-, and 90-min incubations. The beta-adrenergic agonist, isoproterenol, and the adenylate cyclase activator, forskolin, elicited very little secretion in vitro; the 90-min values with isoproterenol were 16.8 +/- 7.1% lingual lipase and 6.0 +/- 2.6% amylase. The alpha-adrenergic agonist, phenylephrine, did not stimulate enzyme secretion. Morphological assessment of incubated tissues revealed that carbachol induced a rapid and extensive degranulation of the acinar cells, while isoproterenol caused only minimal exocytosis. In vivo stimulation by the cholinergic agonist, pilocarpine, caused rapid secretion, with maximal secretion occurring by 1 h. In vivo secretion stimulated by isoproterenol was slow, but by 4 h secretion was comparable to that induced by pilocarpine. In vitro, there was a significant difference between the percentages of lingual lipase and amylase secreted, which could not be accounted for by the presence of proteases or microbial products or the lack of stability of the enzymes during the incubation period. Neurotransmitter regulation of protein secretion by the lingual serous (minor salivary) glands appears to be principally cholinergic in contrast to the beta-adrenergic stimulation of protein secretion by the parotid (major salivary) gland.