Histological and ultrastructural study of the effects of cholinergic and adrenergic agonists on salivary secretion from the lingual epithelium and the lingual gland of the Tokyo Daruma pond frog

Abstract

Comparative observations of the effects of cholinergic and adrenergic agonists (such as pilocarpine, phenylephrine and isoproterenol) on the secretion of salivary fluid and of secretory granules from the lingual epithelium and the lingual gland in the Tokyo Daruma pond frog, Rana porosa porosa, were made by light and transmission electron microscopy. The effect of pilocarpine on the loss of cytoplasm in both the lingual epithelium and the lingual gland was the strongest, and that of isoproterenol was the weakest. Transmission electron microscopy revealed that electron-dense granules, located in cells in both the lingual epithelium and the lingual gland, were discharged by exocytosis after stimulation by phenylephrine and isoproterenol. Immediately before secretion of these granules, they became somewhat larger and round or distorted in shape. However, after administration of pilocarpine, no obvious discharge of electron-dense granules was apparent and, instead, granules in some cells began deteriorating within the cells and those in other cells developed electron-dense and electron-lucent areas. A dot-like pattern was recognized in the electron-dense areas of these granules. These phenomena were assumed to be secondary effects accompanying the secretion of salivary fluid from cells of the lingual epithelium and the lingual gland. By contrast, mucous granules in the lingual gland were secreted by a holocrine process.