Histological and ultrastructural studies of the effects of tachykinins on protein secretion from the lingual epithelium and the lingual gland of the Tokyo daruma pond frog (Rana porosa porosa)

Four tachykinins were each administered at 20 μg/kg body wt. All the tachykinins had a positive effect on granular secretion from the lingual epithelium, and the loss of cytoplasm from cells of the lingual epithelium was greatest with physalaemin and eledoisin, moderate with neurokinin A, and smallest with substance P. These reactions were very different from those in mammals, in which tachykinins induce only watery secretions. Only physalaemin had a positive effect on protein secretion from the lingual gland. Transmission electron microscopy revealed that electron-dense granules in cells of the lingual epithelium were discharged during stimulation with physalaemin and eledoisin by typical exocytosis. Discharge of these granules was indistinct after the administration of substance P and of neurokinin A. Exocytosis of electron-dense granules from cells of the lingual gland was clearly detectable by electron microscopy after the administration of physalaemin, reflecting observations made by light microscopy. However, mucous granules in the lingual gland were secreted by an exocrine process only after administration of physalaemin.