The messenger mechanisms mediating corticotropin regulatory signals in adrenal cortex are studied. We have measured the secretion of corticosteroids, levels of ERK1/2, JNK, p38 mitogen-activated protein kinases, and transcription factors c-jun and c-fos in adrenal cortex of rats after the corticotropin treatment. ACTH increased the ERK1/2 level by a factor of 1,5 in adrenocortical tissue. The level of ERKl/2 was decreased in 6 h after the corticotropin injection. ACTH influence on the JNK level is very significant. The protein kinase JNK level was 2 times higher after 1 h and decreased after 6 h of the corticotropin treatment. The level of p38 kinase was not changed under these conditions. The role of the transcription factor AP-1, which includes the c-fos and c-jun factors, attracts attention in realization of corticotropin signal transduction. C-jun was increased 2-fold by 1 h, and c-fos was increased 1,7-fold after 6 h of ACTH treatment. Together these findings suggest that JNK kinase and the transcriptional factor c-jun mediate the fast corticotropin signal transduction in adrenocorticocytes.