Immunohistochemical demonstration of adenohypophyseal hormones during postnatal ontogenesis in the Gray Short-tailed Opossum, Monodelphis domestica (marsupialia).

Antibodies against human FSH, LH, TSH, ACTH, GH, PRL, and MSH were applied to paraffin sections of newborn (< 1) and pouch-young individuals with the age of 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 13, 14 days, respectively (D1, D2,...). In the pouch-young, the antibody reactions occurred only in the pars distalis of the adenohypophysis. The D < 1 individuals included, the reactions were strong for ACTH, moderate/strong for GH, and moderate for MSH. Reactivity for TSH was recorded first in D2 specimens, for LH in D3 animals, for FSH and PRL in D8 animals. There was a remarkable regional distribution of reactive cells within the pars distalis: reactions for ACTH were localized mainly in the rostral area, those for GH were most prominent caudally. The chronological sequence of appearance of the specific hormone-producing cells in the pouch-young generally is in accordance with the characteristic pattern known in other mammalian species. The late onset of differentiation of some cell types indicates the research possibilities that postnatal Monodelphis domestica can offer in the field of ontogenetic studies on the mammalian endocrine system.