Comparative study in vivo and in vitro of the differentiation of immunoreactive corticotropic cells in fetal rat anterior pituitary.

In order to study the mechanisms of the differentiation of adenohypophysial corticotropic cells, an immuno-cytological study was performed in fetal rat anterior pituitary in vivo and in vitro with antisera against beta-(1-24) and alpha-(17-39) ACTH and beta-LPH, alpha- and beta-endorphins. In vivo, these cells appeared at 16 days of gestation without any difference in the timing of appearance of the two immunoreactivities. The same immunoreactivity was also detected in adenohypophysial primordia explanted from 12 to 15 days of gestation and maintained in organ culture until 21 days by using either medium containing fetal calf serum or medium containing insulin and transferrin instead of fetal calf serum. These immunoreactive cells were first detected in the different experimental primordia after a minimal period of culture, corresponding to a final equivalent of 16 days as in vivo. However, the mean cytoplasmic area of immunoreactive cells increased in relation to the day of explantation whatever the duration of culture. These data suggest: (1) the nature of culture medium used in this study has no influence on the differentiation of the corticotropic cells; (2) this cell type seems to be committed precociously (before day 12) by one or several substances of unknown origin; (3) the normal development seems to require the presence of factors (before day 14) whose nature and origin remain to be elucidated.