Immunocytochemical and morphometric study of prolactin cells during amphibian morphogenesis

The peroxidase-antiperoxidase (PAP) immunocytochemical technique and rabbit antihuman prolactin (PRL) antiserum were used to localize and identify PRL-producing cells in the pars distalis of Bufo calamita, Hyla meridionalis, Alytes cisternasii, Pelobates cultripes, and Rana perezi tadpoles at different stages of development as well as in 1-year-old post-metamorphic animals. This cell type was located throughout the gland in P. cultripes and R. perezi and in the caudal two-thirds in B. calamita, H. meridionalis, and A. cisternasii in premetamorphic animals. These distribution patterns do not show changes throughout development. Morphometry was used to evaluate the changes observed in pars distalis volume and stereological parameters of PRL immunoreactive cells during development. Pars distalis volume increased during the larval growth period and decreased throughout the metamorphic climax. PRL volume density and cellular area showed different patterns in the different species, although the correlation between these parameters suggests a period of great proliferative rate followed by changes in cellular size. The changes observed in PRL total volume suggest the existence of two phases in amphibian development: (i) a period of PRL storage during pre- and prometamorphosis and (ii) a period of release at the metamorphic climax.