The influence of cortisol on the ACTH-producing cells in the pituitary gland of the chick embryo: An immunocytochemical study

The response of 11-day-old chick embryos to exogenous cortisol is explored by the injection of eggs with 1, 10, 50, 100, and 1000 ng of cortisol. Pituitaries, collected 1 hr after each concentration of cortisol and 48 hr after injection of 1000 ng of cortisol, are processed for paraffin embedding and sectioned at 7 μm. ACTH-producing cells are identified with the immunoperoxidase technique employing rabbit antisera against bovine ACTH. Immunoreactive ACTH (Ir-ACTH) positive cells are restricted to the cephalic lobe of the pars distalis and corresponded with the chromophobes of Ehrlich's hematoxylin and eosin stain. Low doses of cortisol from 1 to 100 ng result in an increase accumulation of ACTH within the ACTH cells and also an increase in the numbers of Ir-ACTH-positive cells. At higher concentrations of cortisol (1000 ng), cells are totally depleted of their ACTH granules within 1 hr and are not identifiable with the immunoperoxidase technique. The ACTH cells 48 hr later, however, recuperate showing ACTH-positive granules within the cytoplasmic matrix. It is concluded that cortisol is an active hormone in chick embryos that influences the ACTH cell population via the classical negative feedback mechanisms.