ACTH released from the pituitary acts through activation of cAMP/PKA in adrenocortical cells stimulating steroidogenesis. Although ACTH was originally thought to have anti-proliferative effects on the adrenal, recently it has been described that it could also have proliferative effects acting through other signalling cascades. This is also relevant in humans given the increased levels of ACTH occurring together with adrenal cortex hyperplasia observed in Cushing’s disease and possibly in other situations such as chronic stress. One of the signalling pathways regulating cell proliferation is the extracellular signal regulated kinase (ERKs) pathway. ERKs are members of the MAPK family of cascades. They are activated by extracellular stimuli such as growth factors and mitogens, become phosphorylated through MEK1/2 and regulate a diversity of cellular processes such as proliferation and differentiation. Until now, no study addressed the effects of chronic ACTH administration on the activation of ERKs in vivo. Using rats submitted to different ACTH dosages as well as variable durations, we determined if ACTH induced ERKs activation and by establishing a parallelism with proliferating cell nuclear antigen (PCNA) expression, we aimed to demonstrate a role of ACTH-induced ERKs activation in cell proliferation. Blood was collected for hormonal analysis and the role of ACTH-induced ERKs activation in the stimulation of steroidogenesis was also studied. We confirmed that ACTH increased adrenal weight and corticosterone levels when compared with control or dexamethasone-treated animals. We also demonstrated that ACTH increases ERKs activation and PCNA expression in a time- and dose-dependent manner. When ERKs activation was blocked by the use of a specific MEK inhibitor (PD98059), there was a decrease in ACTH-induced corticosterone release and PCNA expression. We conclude that chronic ACTH induces ERKs activation and that this plays an important role in the induction of cell proliferation as well as steroidogenesis.
Jorge G Ferreira, Célia D Cruz, Delminda Neves and Duarte Pignatelli
P Vendeira, D Pignatelli, D Neves, MM Magalhaes, MC Magalhaes and GP Vinson
Adrenocortical regeneration after adrenal autotransplantation provides a model for the study of local autocrine/paracrine mechanisms involved in the growth and differentiation of the adrenal cortex. To study the possible involvement of some growth factors, namely basic fibroblast growth factor (bFGF, FGF-2) and insulin-like growth factor I (IGF-I), in cell differentiation, immunohistochemical and ultrastructural studies were carried out on adrenal autotransplants in adult male rats. To distinguish between fasciculata and glomerulosa-like cells with accuracy, tissue sections were immunostained with IZAb, which recognizes the inner zone antigen (IZAg) present in fasciculata and reticularis cells but absent from the glomerulosa, and by electron microscopy. IGF-I-treated animals exhibited a clear glomerulosa-like zone that was devoid of IZAb immunostaining. In this outer subcapsular area, ultrastructural examination showed cells containing mitochondria with irregular cristae resembling those of the fetal or immature glomerulosa cells. In contrast, no significant morphological differences were observed in bFGF-treated animals when compared with those from saline-treated controls, in both of which, IZAb immunostaining occurred in almost all adrenocortical cells, with no clear zonation or glomerulosa, as seen in the intact animal. Plasma aldosterone and corticosterone concentrations were lower in autotransplanted control animals than in intact controls, although plasma renin activities were similar. IGF-I treatment significantly increased aldosterone concentrations, whereas corticosterone and plasma renin activity were reduced. bFGF infusion further reduced plasma aldosterone, although plasma renin activity and corticosterone were unaffected. These results suggest that the two growth factors have different effects on zonal differentiation and function in the autotransplanted gland. In particular, bFGF, by reducing glomerulosa function, appears partly to replicate the actions of ACTH in normal animals. In contrast, IGF-I enhances the glomerulosa secreting phenotype and diminishes that of the fasciculata/reticularis, possibly replicating the actions of angiotensin II or a low sodium diet.
P Vendeira, D Pignatelli, D Neves, M M Magalhães, M C Magalhães, M M Ho and G P Vinson
Adrenal gland autotransplantation, an interesting model of adrenal regeneration, provides the reconstruction of distinct functional and morphological zonae. An immunohistochemical study of the adrenal gland of adult male rats after autotransplantation and endothelin-1 (ET-1) stimulation was carried out. The technique involved total adrenalectomy and immediate autotransplantation of small adrenal pieces under the skin of the dorsal region. The animals were killed 90 days after the autotransplantation and 1 h after intravenous ET-1 administration. Sections of recovered adrenal grafts were incubated with IZAb, a monoclonal antibody which interacts with an antigen (IZAg) predominantly found in rat adrenal inner zones. Saline-treated control autotransplanted animals showed IZAb immunostaining in almost all adrenocortical tissue, with the exception of small clusters of cells beneath the capsule. ET-1-treated animals exhibited an extended zone devoid of immunostaining and located in the subcapsular area. In addition, ET-1-stimulated animals showed significant increases in aldosterone as well as corticosterone concentrations in plasma. These results revealed that ET-1 stimulated the development of an extended subcapsular zone lacking IZAg expression, an effect that suggests its role in zona glomerulosa induction in these animals.
Journal of Endocrinology (1996) 149, 497–502