Differentiation behavior of pituitary cells in normal and metamorphosis-arrested larvae of the salamander Hynobius retardatus.

When premetamorphic larvae of the salamander Hynobius retardatus were treated with potent goitrogens, or subjected to thyroidectomy, their metamorphosis was completely arrested. The pituitary gland of the arrested larvae consisted mostly of the hypertrophied Thyroid Stimulating Hormone (TSH) cells that are called "thyroidectomy cells". The development and dynamics of the TSH cells were studied by investigating uptake of BrdU into pituitary cell nuclei and by double-staining immunohistochemistry using anti-pituitary specific antibodies. The majority of the BrdU-positive cells expressed the TSHbeta antigen, suggesting that TSH cells increased in number by their extensive proliferation in the pituitary glands of the goitrogen-treated larvae. On the other hand, double-staining immunohistochemistry showed that several prolactin (PRL) immunoreactive cells coexpressed TSHbeta within single cells even in normal controls. Furthermore, pituitary cells coexpressing PRL and TSHbeta increased in number in the goitrogen-treated larvae. Whereas cells coexpressing GH and TSHbeta were not observed in normal controls, they appeared in the pituitary glands of the goitrogen-treated larvae. These results provide morphological evidence for considerable phenotypic plasticity in the pituitary cells of H. retardatus.