Lectin histochemical study of early postnatal vascularization of the developing pars distalis adenohypophysis of the gray short-tailed opossum (Monodelphis domestica, Marsupialia).

Individuals from 18 litters between 0.5 day and 13 days post partum, and two adult specimens of Monodelphis domestica (Marsupialia), were studied by TEM and lectin histochemistry. Positive reactions for PO-lectins in the developing pituitary were found in the vascular and/or perivascular elements; secretory cells did not react. Positive vascular reactions varied with both the type of lectin and the age of the developing animal. In the adults, the reactions were reversed: there were no vascular, but a variety of positive cellular reactions. It is concluded that the adenohypophyseal blood vascular system is very far from being complete and mature in the newborn M. domestica. According to specific data taken from the literature, the lectin histochemistry indicates a sequential appearance of several components of the extracellular matrix, suggesting also that the actively organ-invading capillaries may be a good model for the study of basement membrane development.