ACTH modulates ERK phosphorylation in the adrenal gland in a time-dependent manner

ACTH is known to act through the activation of cAMP/PKA in adrenocortical cells, but it has been suggested that it could also act via other pathways such as the ERK 1/2 cascade. To determine the effects of ACTH administration at sequential time points on the activation of ERKs 1/2, groups of rats (n = 6/group) were subjected to i.p. injections of either ACTH (Synacthen Depot-0.2 mg/Kg), or saline (Ct). The animals were sacrificed and the adrenal glands collected at different timings after ACTH injection (2 h, 18 h and 24 h). Two additional groups were injected daily until sacrifice (3 days and 15 days). Blood was collected for analysis and the adrenals were used for immunohistochemistry or Western Blot (WB) analysis. Immunoreactivity was scored by counting the mean number of zonae fasciculata (ZF) and reticularis (ZR) positive cells/section (mean +/- SEM). Adrenal weight was increased by ACTH in comparison with Ct. Corticosterone levels, as expected, were higher in ACTH treated animals than in Ct. The number of pERK positive cells increased in a time-dependent manner until 3d, and declined although not significantly in the 15 days animals (Control--48.13 +/- 9.0; ACTH 2 h--125.93 +/- 14.5; ACTH 18 h-139.46 +/- 10.0; ACTH 24 h--185.28 +/- 13.3; ACTH 3 days--198.47 +/- 18.6; ACTH 15 days--158.58 +/- 15.1). Comparable results were obtained with WB analysis. Our data shows that ACTH induces the activation of the MAPK/ERKs 1/2 cascade, especially in the ZF, consistent with this zone being more responsive to ACTH.