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, a nd two adult specimens of Monodelphis domestica (Marsupialia), were st udied by TEM and lectin histochemistry. Positive reactions for PO-lect ins in the developing pituitary were found in the vascular and/or peri vascular elements; secretory cells did not react. Positive vascular re actions varied with both the type of lectin and the age of the develop ing animal. In the adults, the reactions were reversed: there were no vascular, but a variety of positive cellular reactions. It is conclude d that the adenohypophyseal blood vascular system is very far from bei ng complete and mature in the newborn M. domestica. According to speci fic data taken from the literature, the lectin histochemistry indicate s a sequential appearance of several components of the extracellular m atrix, suggesting also that the actively organ-invading capillaries ma y be a good model for the study of basement membrane development.