Apoptotic cell death in the rat adrenal gland: An in vivo and in vitro investigation

Adrenocortical cell apoptosis was studied by using an established in vivo model, the hypophysectomized rat, and an in vitro model, viz., rat adrenal glands in short-term organ culture. In vivo, apoptosis (biochemical autoradiographic analysis of internucleosomal DNA cleavage) was weak and not apparent until 12-24 h after hypophysectomy. In situ histochemical localization of 3'-end DNA strand breaks revealed that apoptosis in vivo occurred nearly exclusively in subpopulations of zona reticularis cells. Adrenocorticotropic hormone (ACTH) maintenance completely blocked these indices of apoptosis. By contrast, apoptosis (DNA fragmentation) in cultured rat adrenal glands without ACTH was extensive and relatively rapid, being apparent after 1 h and increasing with the duration of incubation. ACTH attenuated (by 44%) but did not completely block apoptosis in vitro. Thus, ACTH appears to be the sole pituitary hormone that forestalls apoptosis of terminally differentiated adreneocortical (zona reticularis) cells. However, the discrepancy between in vitro and in vivo models in terms of the magnitude and rate of DNA fragmentation suggests that, in vivo, other factors finely regulate the magnitude of adrenocortical apoptotic cell death.