Adrenocorticotropic hormone elevates gene expression for catecholamine biosynthesis in rat superior cervical ganglia and locus coeruleus by an adrenal independent mechanism.

Classically, upon hypothalamic stimulation, adrenocorticotropic hormone (ACTH) is released from the pituitary and acts on melanocortin 2 receptors (MC2R) in the adrenal cortex, stimulating glucocorticoid synthesis and release. Our earlier studies suggested that ACTH might have a direct effect on sympathetic ganglia. To analyze further the involvement of ACTH in regulation of gene expression of norepinephrine (NE) biosynthetic enzymes, we examined the effect of bilateral adrenalectomy (ADX) of Sprague-Dawley male rats. Fourteen days post-ADX, as expected, plasma ACTH was elevated, and levels of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and MC2R mRNAs in superior cervical ganglia (SCG), and TH mRNA in locus coeruleus (LC) were increased compared with sham-operated animals. To determine effect of pulsatile elevation of ACTH, corticosterone pellets were implanted to ADX rats. Similar to immobilization (IMO) stress ACTH injections to these animals caused a rise in ACTH in plasma and triggered elevation of TH and DBH mRNAs in SCG and in LC with single and repeated daily injections, and MC2R mRNA in SCG with single injections. To study the effect of ACTH in isolated cells, primary cultures of rat SCG were transfected with TH and DBH promoter constructs and treated with ACTH. In agreement with the in vivo data, ACTH elevated their promoter activities similar to levels triggered by cyclic AMP analog. ACTH in the human SK-N-SH neuroblastoma cells increased TH and DBH promoter activity and endogenous DBH mRNA levels. The results show that ACTH can have a direct effect on transcription and gene expression of NE biosynthetic enzymes even without contribution of adrenal hormones.