Atrial natriuretic factor (ANF)-like immunoreactivity and secretory granules in internal gills tadpoles of South American toad Bufo arenarum (Hensel).

In this study, an ultrastructural and immunohistochemical analysis was carried out on the presence of Atrial Natriuretic Factor-like substance in the internal gills of premetamorphic larval stages of the South American toad. The results of immunohistochemical study indicate that, at larval 27 and following stages, ANF-like immunoreactive cells are seen in internal gills. At electron-microscopy level "secretory granules" similar to those ANF-immunoreactives granules of myoendocrine cells of the same species are seen only in clear cells of gill rakers. Our results reveal the occurrence of ANF-like substance in Bufo arenarum gills and may suggest that "cardiac hormones" might play a paracrine and/or autocrine role in the water and electrolyte balance at internal gills level.