Ultrastructural localization of immunoreactive calcitonin in the two cell types of the ultimobranchial gland of the common toad (Bufo bufo L.).

The ultimobranchial (UB) glands of the common toad Bufo bufo consist of several cellular masses containing two quite different cell types which line a central lumen filled with amorphous material. The morphologically defined Type I cell is akin to a typical calcitonin secretory cell as observed for all vertebrates, with small dense-core secretory granules. On the contrary the Type II cell displays large apical dense bodies which may be related to the secretion and/or absorption of the amorphous material. Cells morphologically related to Type II cells have been described in the UB glands of Sauropsidea and in the UB follicles of mammalian thyroid gland. An immunocytochemical stain using an antiserum raised against synthetic salmon calcitonin demonstrated the specific localization of an immunoreactive product in both Type I and Type II cell granules, suggesting that both cell types could be involved in calcitonin metabolism. Moreover, the presence of immunoreactive calcitonin in the Type II cells of the Bufo UB gland raises the question of the function of the morphologically equivalent cells of other species.