Calcium ion as "second messenger" in corticoidogenic action of ACTH

The correlation between corticoidogenesis and Ca2+-influx in the cell was investigated using isolated rat or bovine adrenocortical cells. 1) ACTH-induced corticoidogenesis in both rat and bovine adrenocortical cells was enhanced in parallel with increasing concentration of external Ca2+. In the bovine cells but not in the rat cells, moreover, the marked stimulatory effect of external Ca2+ on the corticoidogenesis was observed despite the absence of ACTH. 2) Ca2+-influx and corticoidogenesis always occurred unitedly. 3) Verapamil markedly inhibited either corticoidogenesis or Ca2+-influx in response to ACTH. 4) The stimulatory effect of Ca2+ on corticoidogenesis was completely blocked by cycloheximide. It was therefore suggested that Ca2+ could regulate corticoidogenesis as a primary "second messenger" of ACTH through biosynthesis of so-called steroidogenic protein.