Immunocytochemical and morphometric study on the changes of TSH, PRL, GH and ACTH cells during the development of Bufo arenarum.

The development and dynamics of thyrotropin (TSH), adrenocorticotropic hormone (ACTH), prolactin (PRL), and growth hormone (GH) cells have been studied using immunocytochemical techniques and rabbit antisera, raised against the relevant human hormone, in the pars distalis of Bufo arenarum larvae at different stages of development. The four types of cells studied were identified in different zones of the pars distalis: TSH cells occurred mainly in the centro-ventral zone, ACTH cells in the rostral and dorsal zones, GH cells in the central and caudal zones, and PRL cells in the anterior two-thirds of the gland. This distribution pattern does not show significant changes with development. Morphometry and stereology were used to evaluate the changes observed in the volume of the pars distalis and the immunoreactive cells during development. The former increased during larval growth and decreased throughout the metamorphic climax. The results obtained on cell number, volume density, and total volume suggest that, during larval growth (pre-prometamorphosis) of B. arenarum, TSH, PRL, GH and ACTH cells show a proliferative period with storage of their hormones; a second period involving hormone release occurs at the metamorphic climax.