Direct effects of adrenocorticotropic hormone on bovine adrenomedullary cells: adenosine 3',5'-monophosphate-dependent phosphorylation of tyrosine hydroxylase.

Release of adrenal catecholamine by carbachol has been shown to be coincident with an increase in intracellular cAMP levels. Bovine adrenal medullary (BAM) cells were prepared and maintained in culture and used to examine the role of cAMP in stimulus-secretion coupling. The addition of ACTH to these cells caused a 10- to 50-fold increase in cellular cAMP without an effect on catecholamine secretion, suggesting cortical cell contamination. Percoll density separation of both BAM cells and adrenal cortical cells revealed that the greatest cAMP responses to ACTH corresponded to the catecholamine-containing cell fractions and not to those density layers where cortical cells sedimented. BAM cells isolated on Percoll did not metabolize [14C]cholesterol to steroids as would be expected were the ACTH-stimulated cAMP accumulations due to cortical cell contamination of the cultures. ACTH stimulated protein phosphorylation in 32P-labeled BAM cells in a manner indistinguishable from that induced by carbachol and forskolin. The major soluble phosphoprotein to be affected by these agents had a relative mol wt of 55-57 kdaltons on sodium dodecyl sulfate-gels and corresponded to tyrosine hydroxylase, which is a specific marker enzyme in the adrenal for chromaffin cells. We propose that bovine adrenal chromaffin cells express ACTH receptors which are coupled to adenylate cyclase. While no acute effect of ACTH was found on catecholamine secretion, ACTH may play a direct role in the regulation of catecholamine synthesis by stimulating the phosphorylation of tyrosine hydroxylase by cAMP-dependent protein kinase.